Problem engines.

[Perry Rose]

I scratch built a .20/.25 size profile. 44 inch span 3/8 fuselage with a 1/4 tripler over 1/16 ply doublers. Set up for the FP .20 and .25 LA and a tongue muffler. I installed two .156 spray bars and needles and tried a remote nva with the stock .136 spray bar and a .156 spray bar. I have used 2 Du-Bro plastic 4 ounce tanks and I built a metal tank. 9 x 4 and 10 x 4 apc's and a 9 x 5 top flite and a 9x4 BY&O. 2/23 fuel 50/50 oil with Armor All added. From the first flight with the engine just below 2 cycle when I pull the launch rope the engine goes lean. No change when using any of the 3 tanks or 2 engines or props or any combination of them. I added another 1/4 inch quadroupler on the right side. Nice hard balsa. No change at all. I set the needle to bubbling rich and the engine still speeds up but not quite as much.
  I have run out of ideas. There must be some vibration present somewhere that I haven't found.  What should the venturi size be that is another area I haven't changed?
  The plane flys too good to put in the raffle.

[Dennis Toth]

Perry,
Search this forum for the FP 20 set up that Brett Buck suggests. It is basically a stock engine, muffler, venturi and NVA. They set up a tall skinny tank on conventional venting and muffler pressure. The 9x4 APC is the starting point prop. Set for a steady 2 cycle. Something like 10%N, 22% total oil (50/50 is good). Adjust line length for comfortable lap time.

One thing on the profile if not muffler pressure make sure the vent is up in the free air flow above the fuse side profile either on the inside of the fuse or at least on top.

Best,    DennisT

[Dan McEntee]

   I would say you still have some sort of air leak, or the engine would richen up a bit when you reach flying speed. When you release the model is should speed up a bit and then go back to a richer setting from centrifugal force increasing the fuel head. Try shimming the back of the tank out at least 1/8" and see what happens. Also, some will question the Armor-All in the fuel, but I use just a few drops per gallon when I apply it as needed. How much do you add to your fuel? And the usual advice to make sure the spray bar hole is pointing down. You don't mention the venturi diameters. if using a stock OS remote needle and spray bar, make sure the diameter is on the small side. you could try stuffing a stick into the venturi to reduce the area also just as a quick test. But I would be looking for some other source of an air leak.
  Type at you later,
   Dan McEntee

[Colin McRae]

I have 3 OS 25LA-s engines on models, and all run great. One is totally stock w/ remote NVA, and the other 2 are stock except that I use a front NVA that I got from shtterman (the Control Line Store on eBay). And I run them w/ the OS stock tube muffler with baffle installed. The 25LA-s engine runs best stock in my experience. The stock spray bar is 0.137" and the venturi is 0.236". And I don't run 4-2-4. My experience is that the 25LA runs best with the needle set at maybe 30 deg open from peak rpm (just like the owner's manual says). On 10% nitro / 20% oil I usually get around 12,500 rpm on an APC 9-4 sport prop. I also use a uniflow tank w/ muffler pressure. Tank centerline height about 1/8" above the spray bar center.

I once tried a tongue muffler and did not like how the engine ran. Went very lean in maneuvers as you are experiencing. The tongue muffler might be part of your issue. I would try the stock OS muffler w/ baffle installed. 

[Colin McRae]

One other thing. Your initial post says 2/23 fuel. ??  Does that mean 20% nitro? If so, to me that is way too much. Try 5 or 10% nitro.

[Perry Rose]

I use a few drops of Armor All also. I leak tested the entire system inside and out hoping to find a leak but nothing out of the ordinary. I measured the venturi and its close to .300 on both engines. I scrounged around and found a home made one that is close to .250 and installed it on the FP .20 that is in the plane with a .156 spray bar. I have a stock O.S. nva if needed. I don't have time to test it now maybe late afternoon. If it now works I'll have to re finish the fuselage as I wasn't too careful installing the quadroupler.
  The fuel is 2% nitro. I mix my own. 4 gallons of 0% nitro (FAI fuel) and one gallon of store bought 10% nitro and adjust the oil for the 23%.

[Dan McEntee]

I use a few drops of Armor All also. I leak tested the entire system inside and out hoping to find a leak but nothing out of the ordinary. I measured the venturi and its close to .300 on both engines. I scrounged around and found a home made one that is close to .250 and installed it on the FP .20 that is in the plane with a .156 spray bar. I have a stock O.S. nva if needed. I don't have time to test it now maybe late afternoon. If it now works I'll have to re finish the fuselage as I wasn't too careful installing the quadroupler.
  The fuel is 2% nitro. I mix my own. 4 gallons of 0% nitro (FAI fuel) and one gallon of store bought 10% nitro and adjust the oil for the 23%.

       I think that .300" venturi is at the heart of the matter here. The .25" will be closer, but I would acquire a few that are smaller in .005" to .010" increments. I have put aluminum tube sleeves in venturis also to reduce them, if you can find some that fits snug. I flair the end a little bit and file away the ledge, cut a notch at the bottom where it will clear the spray bar  and just push it in. If there is concern about it coming out, just a touch of CA will hold it in place and let you remove it later if needed.
  Type at you later,
   Dan McEntee

[Colin McRae]

I use a few drops of Armor All also. I leak tested the entire system inside and out hoping to find a leak but nothing out of the ordinary. I measured the venturi and its close to .300 on both engines. I scrounged around and found a home made one that is close to .250 and installed it on the FP .20 that is in the plane with a .156 spray bar. I have a stock O.S. nva if needed. I don't have time to test it now maybe late afternoon. If it now works I'll have to re finish the fuselage as I wasn't too careful installing the quadroupler.
  The fuel is 2% nitro. I mix my own. 4 gallons of 0% nitro (FAI fuel) and one gallon of store bought 10% nitro and adjust the oil for the 23%.

I don't have experience with a 20 FP.

But on the 25LA, a 0.300 venturi is way too big. Go back to stock size at 0.236. And if you are trying to use a 0.156 spray bar the case must have been drilled out to allow it to fit. The stock spray bar is 0.137. 

As a comparison point, the 46 LA stock venturi is 0.276 with same 0.137 spray bar.

The 25 LA runs best stock.

The LA engines also are designed around 18% oil per the owner's manual. I use VP 10/18 fuel and add a bit of castor to get 20% oil. I have run Brodak 5/23% (50/50) oil and the engine ran fine, but I think it runs even better w/ 18% or 20% oil max.

[Paul Smith]

Based on your original post this seems like a fuel tank issue.
Are you running either muffler pressure or uniflow?
If you have neither, your engine, or any other, will lean out some on acceleration.
With a four-ounce tank, assuming it's a profile, your fuel pickup may be too far outboard.

Don't mess with oversize venturis.  They reduce suction and don't add much power or speed.
I might suggest a 2-ounce tank with the pickup more inboard.

[Brett Buck]

I scratch built a .20/.25 size profile. 44 inch span 3/8 fuselage with a 1/4 tripler over 1/16 ply doublers. Set up for the FP .20 and .25 LA and a tongue muffler. I installed two .156 spray bars and needles and tried a remote nva with the stock .136 spray bar and a .156 spray bar. I have used 2 Du-Bro plastic 4 ounce tanks and I built a metal tank. 9 x 4 and 10 x 4 apc's and a 9 x 5 top flite and a 9x4 BY&O. 2/23 fuel 50/50 oil with Armor All added. From the first flight with the engine just below 2 cycle when I pull the launch rope the engine goes lean.

  I note the use of the ST spraybar and I don't know what "2/23" fuel might be. But the emphasized bits above seems key - the stock muffler is mandatory to run properly, and you do not run it in a 4-stroke. I would suggest putting it back to stock, but unfortunately you can't easily do that, since it had to be drilled out to fit the oversize spraybar. You can't just put the stock spraybar back in without doing something to take up the extra space. You can't just put the stock spraybar back into the oversize hole, it will not seal up properly unless you do something else.

   The stock venturi is .257. I am not sure where you got the other sizes unless someone had previously gone in and modified it. I can promise you that it will not needle properly with a *** .300  **** venturi even with an ST spraybar, it will be instant screeching lean the second it starts to move. It will be even more hopeless with a stock spraybar and oversize venturi.

    If "2/23" fuel means 2% nitro and 23% oil, you are exacerbating the problem by also making it tougher to needle even though the choke area is greatly reduced.  Using the ST spraybar you have knocked out about 30% of the power, but going to .300 overshot in the other direction.

   Given that, I think this has nothing to do with vibration or the tank. I am not even sure what to tell you to do.  But, you have what you have



     IF you have an undamaged case - that is undamanged from drilling a hole in it for an ST spraybar - use that. Put in a STOCK .257 venturi and a STOCK spraybar or nozzle. Use the STOCK muffler. If that screws up the CG, then add lead to the tail to balance it. Put on a APC 9-4 prop. Use a tank that is no wider than 1 3/4" from the engineUse conventional 10% nitro, 17-20% synthetic blend fuel. If you have 15%, then use that.  Start the engine, lean it out into a 2-stroke. Then continue to lean it out until the RPM peaks out, and one more click leaner causes it to "sag" lean.  From the peaked out lean setting, back off 3-6 clicks until you get a distinct drop in the RPM but *still in a 2-stroke*. If it goes into a 4-stroke, that is too far, you have to launch it in a 2-stroke.    Launch it, it may be too fast, but do the maneuvers anyway. If it goes over the top lean at any point, on the next flight, set it *one click* richer, fly again, repeat test. If it drops into a 4-stroke anywhere in the flight, set it *one click* leaner on the next flight, repeat test.

   
DON'T ANYONE ELSE DO THIS INTENTIONALLY - this is MAKING THE BEST OF A BAD SITUATION!!   But... IF you only have drilled-out cases - Use the God-forsaken ST needle and the drilled out STOCK venturi, that is, .257 ID with a .153ish spraybar hole. USE A STOCK MUFFLER. Everything else is the same as above, the difference will be that it will do everything with far less power. You might be better off if you made a "25-sized" airplane, this may be to your benefit because the stock engine is likely far, far, too powerful for your airplane.

      If there is any way to get any of the engines back to stock, please do so, in particular STOCK SPRAYBAR, STOCK VENTURI, and STOCK MUFFLER so at least we know what we are dealing with.  As mentioned in every previous post on the topic, these are all key and any deviation almost always ends with problems like you are having.

     I am sorry you are having problems, but your experience is all too common, if you do not use the engine STOCK out of the box with ALL THE STOCK PARTS, you absolutely will have these sorts of problems. You are exacerbating it by trying to run it in a 4-stroke, which is typically not sufficient stable (and for sure isn't if you modify the engine), and if I am understanding, virtually no nitro and probably excessive oil.

     Brett

   

[Colin McRae]

  I note the use of the ST spraybar and I don't know what "2/23" fuel might be. But the emphasized bits above seems key - the stock muffler is mandatory to run properly, and you do not run it in a 4-stroke. I would suggest putting it back to stock, but unfortunately you can't easily do that, since it had to be drilled out to fit the oversize spraybar. You can't just put the stock spraybar back in without doing something to take up the extra space. You can't just put the stock spraybar back into the oversize hole, it will not seal up properly unless you do something else.

   The stock venturi is .257. I am not sure where you got the other sizes unless someone had previously gone in and modified it. I can promise you that it will not needle properly with a *** .300  **** venturi even with an ST spraybar, it will be instant screeching lean the second it starts to move. It will be even more hopeless with a stock spraybar and oversize venturi.

    If "2/23" fuel means 2% nitro and 23% oil, you are exacerbating the problem by also making it tougher to needle even though the choke area is greatly reduced.  Using the ST spraybar you have knocked out about 30% of the power, but going to .300 overshot in the other direction.

   Given that, I think this has nothing to do with vibration or the tank. I am not even sure what to tell you to do.  But, you have what you have



     IF you have an undamaged case - that is undamanged from drilling a hole in it for an ST spraybar - use that. Put in a STOCK .257 venturi and a STOCK spraybar or nozzle. Use the STOCK muffler. If that screws up the CG, then add lead to the tail to balance it. Put on a APC 9-4 prop. Use a tank that is no wider than 1 3/4" from the engineUse conventional 10% nitro, 17-20% synthetic blend fuel. If you have 15%, then use that.  Start the engine, lean it out into a 2-stroke. Then continue to lean it out until the RPM peaks out, and one more click leaner causes it to "sag" lean.  From the peaked out lean setting, back off 3-6 clicks until you get a distinct drop in the RPM but *still in a 2-stroke*. If it goes into a 4-stroke, that is too far, you have to launch it in a 2-stroke.    Launch it, it may be too fast, but do the maneuvers anyway. If it goes over the top lean at any point, on the next flight, set it *one click* richer, fly again, repeat test. If it drops into a 4-stroke anywhere in the flight, set it *one click* leaner on the next flight, repeat test.

   
DON'T ANYONE ELSE DO THIS INTENTIONALLY - this is MAKING THE BEST OF A BAD SITUATION!!   But... IF you only have drilled-out cases - Use the God-forsaken ST needle and the drilled out STOCK venturi, that is, .257 ID with a .153ish spraybar hole. USE A STOCK MUFFLER. Everything else is the same as above, the difference will be that it will do everything with far less power. You might be better off if you made a "25-sized" airplane, this may be to your benefit because the stock engine is likely far, far, too powerful for your airplane.

      If there is any way to get any of the engines back to stock, please do so, in particular STOCK SPRAYBAR, STOCK VENTURI, and STOCK MUFFLER so at least we know what we are dealing with.  As mentioned in every previous post on the topic, these are all key and any deviation almost always ends with problems like you are having.

     I am sorry you are having problems, but your experience is all too common, if you do not use the engine STOCK out of the box with ALL THE STOCK PARTS, you absolutely will have these sorts of problems. You are exacerbating it by trying to run it in a 4-stroke, which is typically not sufficient stable (and for sure isn't if you modify the engine), and if I am understanding, virtually no nitro and probably excessive oil.

     Brett

   

Brett, I have a question on the OS stock size venturi for the 25 LA. I purchased an OS OEM venturi for the 25 LA from Shtterman. He referred to it as a 6mm size. 6mm = 0.236"

You state above the stock size is 0.257".

Just for my general knowledge, which is correct?

Thanks in advance.

[Dan McEntee]

Brett, I have a question on the OS stock size venturi for the 25 LA. I purchased an OS OEM venturi for the 25 LA from Shtterman. He referred to it as a 6mm size. 6mm = 0.236"

You state above the stock size is 0.257".

Just for my general knowledge, which is correct?

Thanks in advance.

     I have found that new, OEM venturis for  FP/LA .20 through .35/40-46 can be all over the place. That is why a decent dial calipers and the knowledge on how to use it is your best friend!! it can help you check what you bought or what some one claims their venturi is. keep in mind also t6here are two vintages of OS needle valve assemblies, needles and venturis. The original OS spray bars in the black and white header card package are larger than the more recent blue and white. I have a suspicion that some of the LA.25-40/.46 units at the very end were made from excess LA.15 parts, and the needles have less taper and is more blunt than the original FP part. Now the shuttrman has his parts on the market, they may be a bit different yet. he says they are made to OS specs but I think it was the specs for the very end of the parts run. They work, but if the spray bars are a little undersize, you have to allow for and deal with that.  In short, you just can't talk about this stuff in generic terms such as OS or ST any more and expect them to be exactly like the originals were.
  Type at you later,
  Dan McEntee

[Colin McRae]

     I have found that new, OEM venturis for  FP/LA .20 through .35/40-46 can be all over the place. That is why a decent dial calipers and the knowledge on how to use it is your best friend!! it can help you check what you bought or what some one claims their venturi is. keep in mind also t6here are two vintages of OS needle valve assemblies, needles and venturis. The original OS spray bars in the black and white header card package are larger than the more recent blue and white. I have a suspicion that some of the LA.25-40/.46 units at the very end were made from excess LA.15 parts, and the needles have less taper and is more blunt than the original FP part. Now the shuttrman has his parts on the market, they may be a bit different yet. he says they are made to OS specs but I think it was the specs for the very end of the parts run. They work, but if the spray bars are a little undersize, you have to allow for and deal with that.  In short, you just can't talk about this stuff in generic terms such as OS or ST any more and expect them to be exactly like the originals were.
  Type at you later,
  Dan McEntee

Being a curious fellow, I decided to measure myself. The venturi Shtterman sells as 6mm for the 25LA measures a hair over 0.25". So, Brett's 0.257" seems correct. It is definitely larger than 0.236". So I was incorrect.

In any event, my 25 LA w/ 0.257 venturi and stock NVA runs great. In fact, I am running 3 of the stock 25LA's now and they all run great.

[Brett Buck]

Brett, I have a question on the OS stock size venturi for the 25 LA. I purchased an OS OEM venturi for the 25 LA from Shtterman. He referred to it as a 6mm size. 6mm = 0.236"

You state above the stock size is 0.257".

Just for my general knowledge, which is correct?

    I have no idea how my previous post got lost...

   Did you measure it yourself?

  Stock venturi is .257 (using calipers like most people will).    I think the actual nominal value is supposed to be 6.6mm (0.25984) and I have measured them with more accurate methods from about .259xxx to .260xxx. I state it as I get it with calipers, since most people will measure it that way (if at all...) and I DO NOT WANT ANYONE TAKING IT APART to measure it better.

    However, I have a bunch of replacements straight out of the package from OS and measured them. Vernier calipers:



     Using a split-ball gauge:



     Note that the difference is not a matter of calibration of the calipers or mic. There is some touch required, but, if you measure ODs with the same devices, they come out the same to the .001. It's a matter that the calipers have flats on them and it won't go all the way to the full diameter of the hole. Cheapies have wider flats and might measure a few thousandths different. That's actually important if you want to make sense of the results in a more perceptive way, when intentionally changing the venturis.

   In this case, all you need to do is to make sure the venturi is STOCK, you do not want to adjust it or change it, you want the STOCK venturi, spraybar, etc. and all you can do without taking the engine apart is a check from the outside with calipers to see if someone has screwed you up by altering it from the stock configuration.

     Brett


P.s. regarding them being "all over the place". I have not found that to be the case at all, they are pretty accurate - +-.001. Most of the apparent variability is probably differences in the accuracy of the measurement based on which calipers are used and the "touch" used to measure it. You can pretty easily pull in another few thousandths by pushing harder, and in my example above, by really cranking down on the adjuster drum. Others, with no fine adjustment, you can't really control the pressure.

  Another factor is that at this point, there are so many people out there "fixing" them, you might have a stock-looking venturi that someone has already drilled out to Get More Power. There are probably serial production changes over many years but pretty much all the FPs of various sizes have been consistent over the period of decades.


p.p.s  As far as measuring goes, I am not a huge fan of any of my digital micrometers or calipers. My calipers (a real Mitutoyo 6" digital, and a counterfeit Mitutoyo 12") are mostly OK, but the digital mic perpetually runs the battery down, and because it doesn't have the vernier scale so you can't get closer to eyeballing it to the tenth (note the measurement in the picture looks like it's about 20-30% of the way between lines, the actual value is .2602xx) without a battery. I much prefer vernier calipers over dial, but you have to do differential measurements manually instead of being able to set the dial 0 as you want.

    Note that the absolute accuracy of all these items, to the thousandth or so, is excellent, you get accuracy to the degree you can measure. For almost all applications in modeling, you need no more than maybe about .002" of accuracy. For those few applications  where you need more than that, down in the tenths of thousandths,  it becomes a much more complicated matter and you have to consider many other factors than just the accuracy of the instruments (like the temperature). 

     

[Colin McRae]

    I have no idea how my previous post got lost...

   Did you measure it yourself?

  Stock venturi is .257 (using calipers like most people will).    I think the actual nominal value is supposed to be 6.6mm (0.25984) and I have measured them with more accurate methods from about .259xxx to .260xxx. I state it as I get it with calipers, since most people will measure it that way (if at all...) and I DO NOT WANT ANYONE TAKING IT APART to get to measure it better.

    However, I have a bunch of replacements straight out of the package from OS and measured them. Vernier calipers:

     Note that the difference is not a matter of calibration of the calipers or mic. There is some touch required, but, if you measure ODs with the same devices, they come out the same to the .001. It's a matter that the calipers have flats on them and it won't go all the way to the full diameter of the hole. Cheapies have wider flats and might measure a few thousandths different. That's actually important if you want to make sense of the results in a more perceptive way, when intentionally changing the venturis.

   In this case, all you need to do is to make sure the venturi is STOCK, you do not want to adjust it or change it, you want the STOCK venturi, spraybar, etc. and all you can do without taking the engine apart is a check from the outside with calipers to see if someone has screwed you up by altering it from the stock configuration.

     Brett


P.s. regarding them being "all over the place". I have not found that to be the case at all, they are pretty accurate - +-.001. Most of the apparent variability is probably differences in the accuracy of the measurement based on which calipers are used and the "touch" used to measure it. You can pretty easily pull in another few thousandths by pushing harder, and in my example above, by really cranking down on the adjuster drum. Others, with no fine adjustment, you can't really control the pressure.

  Another factor is that at this point, there are so many people out there "fixing" them, you might have a stock-looking venturi that someone has already drilled out to Get More Power. There are probably serial production changes over many years but pretty much all the FPs of various sizes have been consistent over the period of decades.



   

Thanks much Brett.

I was incorrect. I have a crude narrow caliper that has flat insides so cannot accurately measure small ID's. But even so, mine measured slightly over 0.25" so 0.257 is correct as you have more sophisticated tools. I guess Shtterman just calls it 6mm for ease of selling purposes, and to differentiate it from the larger 40/46LA venturi which he refers to as 7mm.

And the venturis I purchased form Shtterman came in OS original packaging so indeed stock OS parts.

[Brett Buck]

Thanks much Brett.

I was incorrect. I have a crude narrow caliper that has flat insides so cannot accurately measure small ID's. But even so, mine measured slightly over 0.25" so 0.257 is correct as you have more sophisticated tools. I guess Shtterman just calls it 6mm for ease of selling purposes, and to differentiate it from the larger 40/46LA venturi which he refers to as 7mm.

And the venturis I purchased form Shtterman came in OS original packaging so indeed stock OS parts.

   No issue, I think we were talking past each other.

    Ultimately, the OPs problem is 100% clear, if he can put everything back to stock, it will likely be perfectly fine. I have seen this same scenario over and over again, pretty much exactly the same down to the details, with very predictable results.

    But as you now see, there is massive amounts of misinformation and wrong ideas floating around, and unfortunately, despite my best efforts, people are still having exactly the same issues over and over again. So, adding another one - like  yet another set of wrong dimensions for the stock venturi - just compounds the issue. So I wanted to make it absolutely crystal clear. Also I included action photos of me actually measuring it less than an hour ago, so no one will email me saying I am an "anti-American con man" or "liar trying to trick people", etc again. Of course, I could have posted the EXIF data, but people have also accused me of faking that.

    I would suggest you trim your quote above, no need to repeat the large photos.

   Brett

[Motorman]

Perry, Something that can cause the problem you have is the position of the vent tube inside the tank. On the ground the air comming out of the vent will miss the feed line. Maybe due to gravity or lower ground rpm. When your in the air things change giving you a stronger air blast from the vent. This can blanket the feed line sending foam to the engine which of course leans the mixture. If you find you have the same problem after fitting the right size venturi, it's something you might look into.

MM

[Perry Rose]

Todays test flight. I had the FP .20 on the plane so I put the .25 muffler on and with the .250 venturi (homemade) and the .156 spray bar it could only get 5.44 seconds per lap at a steady 2 stroke. But it did not run away like it was doing so the large venturi was the problem. I didn't have the tongue muffler to try or another prop. At home I swapped the .20 for the .25LA. I removed the venturi from the .25 and it measured .260 going in from the bottom. A conundrum. Anyway I put homemade .250 venturi and the stock muffler on and the stock remote nva and spray bar. Ran steady on the ground but it did before also. Maybe a test flight later today. I need closer to 5 second laps with this plane.

[Dan McEntee]

P.s. regarding them being "all over the place". I have not found that to be the case at all, they are pretty accurate - +-.001. Most of the apparent variability is probably differences in the accuracy of the measurement based on which calipers are used and the "touch" used to measure it. You can pretty easily pull in another few thousandths by pushing harder, and in my example above, by really cranking down on the adjuster drum. Others, with no fine adjustment, you can't really control the pressure.

  Another factor is that at this point, there are so many people out there "fixing" them, you might have a stock-looking venturi that someone has already drilled out to Get More Power. There are probably serial production changes over many years but pretty much all the FPs of various sizes have been consistent over the period of decades.


p.p.s  As far as measuring goes, I am not a huge fan of any of my digital micrometers or calipers. My calipers (a real Mitutoyo 6" digital, and a counterfeit Mitutoyo 12") are mostly OK, but the digital mic perpetually runs the battery down, and because it doesn't have the vernier scale so you can't get closer to eyeballing it to the tenth (note the measurement in the picture looks like it's about 20-30% of the way between lines, the actual value is .2602xx) without a battery. I much prefer vernier calipers over dial, but you have to do differential measurements manually instead of being able to set the dial 0 as you want.

    Note that the absolute accuracy of all these items, to the thousandth or so, is excellent, you get accuracy to the degree you can measure. For almost all applications in modeling, you need no more than maybe about .002" of accuracy. For those few applications  where you need more than that, down in the tenths of thousandths,  it becomes a much more complicated matter and you have to consider many other factors than just the accuracy of the instruments (like the temperature). 

     I have a younger brother Jim that passed away suddenly in 2012 that had a successful one man operation machine shop in Atlanta, GA. He did some amazing stuff there in an unimaginable wide variety of projects ranging from the most simple devices for keeping track of cook time at Chic-Fillet restaurants to stuff that rode on the Space Shuttle, things for the weapons industry, the medical devices, and things in between that we didn't know about until after he passed away because of confidentiality agreements. Lots of prototypes and one offs such as custom implants for reconstructive surgery and research projects at a Georgia University. Stuff that no one else wanted to bother with because there was no 'real money" to be made with them, but some were pretty damn important. The dude was good !! I had the duty of taking his shop apart to prepare everything to get auctioned off. My sister in law told me to take anything that I thought I might want and could use at work or home. I brought home the stuff that was in his personal tool box such as his mics, calipers,  gauges and other small tools, plus some sets of small pin gauges. Jim had taught me a long time ago that if I was not sure of a caliper measurement on the I.D. of a hole, a pin gauge was probably the best for what I would be doing. It takes some practice to develop the feel and touch for doing this also, but for what we are doing, it's accurate enough and much easier if you have trouble with calipers. Once you have the right pin fitting the ID, then just measure the pin with a micrometer and you don't have to worry about measuring the hole in a specific spot. The shanks of number and letter drills can be substituted for pin gauges, just ignore what the size says on the drill shank and measure it anyway. That's how I came to the findings I have about the ID of what I have being all over the place. That may be too broad of a term, but I was taking venturis out of brand new engines and they were not what was supposed to be in there. I really think that when OS got to the LA series and wanted to close it out, they did what they had to do to get product out the door.  My venturi collection is made up of who knows what came from where because I have accumulated it over many years. But when you go through 6 or 8 new in package parts and find such variations, that makes you wonder. The last run needles in the blue and white header card packages are not anything like other OS needles I have, especially from the FP days, where the spray bars are bigger and the needle valves are longer, have more taper and are sharp enough to draw blood. I haven't bought many of shuttrman's Enya made OS spec needle valve assemblies to compare yet, but the one I did I found that the nut to hold the spray par to the venturi was a bit loose compared to OS nuts that fit his spray bars like they should. I talked to him about it and he was going to go back to Enya about it and I'm sure he got things corrected. But if a mistake were made there, where else could they be made? the only way to be sure is to measure them. New guys getting into this have those skills to learn and be confident in what they are doing, and from what I have seen coming out of OS packaging I would not take anything for granted in what the labels say. If there are counterfeit glow plugs being sold out there, ( and there are ! ) who knows what else might be dropping onto the market in addition to what OS did just to get product out the door.
   Type at you later,
   Dan McEntee
   

[Brett Buck]

Todays test flight. I had the FP .20 on the plane so I put the .25 muffler on and with the .250 venturi (homemade) and the .156 spray bar it could only get 5.44 seconds per lap at a steady 2 stroke. But it did not run away like it was doing so the large venturi was the problem.

    Well, maybe part of the problem, but *the muffler is required to get it to run properly*. Otherwise, you are getting about what I would expect with the venturi choked down by using the improper spraybar. That combination cuts the power by more than 30%. Running it on 2% nitro with excess castor kills even more, and it will varnish up and continue to lose power.

    Again, this is not a new ground you are breaking here, and I these are not educated guesses or "keyboard engine expert"  stuff. I and many others have done all the variations you have, repeatedly, your results are pretty similar to everyone else's. 

    To get it to work, more or less, with the ST spraybar, you need ~.273 venturi (letter I drill or reamer), or you need to restore the drilled-out case somehow to use the stock venturi. There are no appropriate fractional drill sizes, 9/32 is too big. 6.9mm would be the nearest available metric size, 7.0 is pushing it

    If you put the tongue muffler back on, it might get more power, but it will also be all over the place in the air.

At home I swapped the .20 for the .25LA. I removed the venturi from the .25 and it measured .260 going in from the bottom. A conundrum. Anyway I put homemade .250 venturi and the stock muffler on and the stock remote nva and spray bar. Ran steady on the ground but it did before also. Maybe a test flight later today. I need closer to 5 second laps with this plane.

     That will probably work better and certainly have more power. The .260 venturi is stock, with a stock spraybar, you now have the correct choke area. The correct muffler will permit the speed to be controlled. The question mark is the fuel, 2% will make it much more unstable than conventional fuel, and much harder to needle. Mine does not like 5% although it sort of works. 10% is vastly more stable and easier to needle. With the stock backplate needle, on 2%, one click might be too coarse. 10 or 15%, it will be much more reasonable.

    23% with a lot of castor will also slowly varnish it up, and the power will fade over the course of a few dozen flights. I strongly recommend using Powermaster 10 or 15% "Air", that is, the regular RC sport fuel with 17% castor/synthetic blend, or some near equivalent. IF you only have GMA or something like it, I would suggest cutting it 50/50 with equivalent straight synthetic to get rid of some of the castor. It would probably be OK on straight synthetic for a while if you were sure to hit the right needle,  but given your other issues, you might want a little margin.

     I also caution that if you have been running it on your fuel and it has varnished itself up, and you switch fuel to something appropriate, the engine settings will not be very stable over the next 10-20 flights, probably getting richer and requiring a needle tweak leaner every so often. This is because the engine will start to loosen up as the varnish is removed, looser means less drag and better fuel consumption.

    Brett

[Perry Rose]

I got in another flight with the .250 venturi and stock remote spraybar and nva and stock muffler.  Just like the FP .20 it ran well at the suggested setting and had the power to get a good lap speed. It looks like the muffler was the cure. I'm using 58 foot lines and maybe I'll try 56 footers.

[Brett Buck]

I got in another flight with the .250 venturi and stock remote spraybar and nva and stock muffler.  Just like the FP .20 it ran well at the suggested setting and had the power to get a good lap speed. It looks like the muffler was the cure. I'm using 58 foot lines and maybe I'll try 56 footers.

   Go up to the stock venturi and 10%, and you will not be looking for 56 foot lines. Our recurring problem has been excess speed and power, not too little.

    Brett

[John Skukalek]

What is the OD of the stock spray bar for the 25LA?

[Brett Buck]

What is the OD of the stock spray bar for the 25LA?

 

   .137x/ nominal 3.5mm.

    Brett

[John Skukalek]

Thank you Brett

[Dan McEntee]

I got in another flight with the .250 venturi and stock remote spraybar and nva and stock muffler.  Just like the FP .20 it ran well at the suggested setting and had the power to get a good lap speed. It looks like the muffler was the cure. I'm using 58 foot lines and maybe I'll try 56 footers.

     From what I have read here , replacing the .300" venturi with the .250" was the cure. Get some more flights on it , and if you want to shed the nose weight, try your tongue muffler again.  I run tongue muffler on my .25's with no issues. You may want to open up and/or add some holes to it to let the engine breath a bit better. The stock muffler is almost 2 ounces heavier ?? And to counter that you probably have added 1 to 1.5 ounces to the tail?  Depending on the airplane, that can help out how it turns and such.

   Type at you later,
    Dan McEntee

[Brett Buck]

     From what I have read here , replacing the .300" venturi with the .250" was the cure. Get some more flights on it , and if you want to shed the nose weight, try your tongue muffler again.  I run tongue muffler on my .25's with no issues. You may want to open up and/or add some holes to it to let the engine breath a bit better. The stock muffler is almost 2 ounces heavier ?? And to counter that you probably have added 1 to 1.5 ounces to the tail?  Depending on the airplane, that can help out how it turns and such.

      He just finally got it working, two more minor changes and he will have it - and now we are trying to undo the critical fix? The *stock* muffler is absolutely key to getting it to run properly, as proven from dozens of examples just exactly like Perry's.

    I do not know how else to say it - *this is not an experiment* any more, every variant has been tried, not just by me, we know what different changes will do to the system with abundant examples of every variant.

   I also note, he is still down on power due to the .250 venturi, changing back to the .257 venturi would be a very substantial improvement - if it could be needled. With the *stock parts*, it will be hair-trigger to adjust on the weak fuel.

      If he could only make one change from the current, working, system, going to conventional fuel would be the first step. That will make it far more tractable, not to mention adding significant power. He may not need or want to go to the stock venturi afterwards.  The biggest potential issue is excess power (when otherwise set correctly) and not being able to slow it down. On a sufficiently large airplane that is fine, I am not sure about it in this case.

      Brett

p.s. if you don't believe me, https://stunthanger.com/smf/open-forum/s1-ringmaster-power/msg475795/#msg475795

[Steve Helmick]

My .25LA ran nice with stock muffler, .272" venturi and .156" (4mm) spraybar...actually Mecoa/K&B/Veco .19 stuff. I didn't like the rear NV for either starting (manual finger, not the electric finger) or response. The stock OS NV was loose and wobbled in the spraybar, so I 86'd it.  Steve

[Perry Rose]

I got in some flights this morning and it went well. I'm using the 2030 muffler with 0.5 ounces on the tail. 57 foot lines eye to eye and a high four second lap time. That gave me the line tension I need for the
high up and overhead stuff. I'm still using a 9 x 4 BY&O as I broke my last 9 x 4 APC a couple weeks ago. If I remove the spinner and the tail weight the balance would probably return to the starting spot. It's too late to worry about the planes looks anyway.
  Long ago some college student cobbled together a phrase "I think therefore I am". In my case "I model therefore I experiment". The RSM tongue muffler I have has 14 .093 holes which is twice the area of the 2030 muffler outlet.  Now that a base line has been established i can try the tongue muffler to see what happens.
  Right now I am getting 3 mins. 35 secs. engine run/flight time on 2 ounces of fuel.

[Dan McEntee]

      He just finally got it working, two more minor changes and he will have it - and now we are trying to undo the critical fix? The *stock* muffler is absolutely key to getting it to run properly, as proven from dozens of examples just exactly like Perry's.

    I do not know how else to say it - *this is not an experiment* any more, every variant has been tried, not just by me, we know what different changes will do to the system with abundant examples of every variant.

   I also note, he is still down on power due to the .250 venturi, changing back to the .257 venturi would be a very substantial improvement - if it could be needled. With the *stock parts*, it will be hair-trigger to adjust on the weak fuel.

      If he could only make one change from the current, working, system, going to conventional fuel would be the first step. That will make it far more tractable, not to mention adding significant power. He may not need or want to go to the stock venturi afterwards.  The biggest potential issue is excess power (when otherwise set correctly) and not being able to slow it down. On a sufficiently large airplane that is fine, I am not sure about it in this case.

      Brett

p.s. if you don't believe me, https://stunthanger.com/smf/open-forum/s1-ringmaster-power/msg475795/#msg475795

     It's not that I don't believe you, my experience has shown me otherwise. I am not against the stock muffler but on some airplanes it make no sense to add that boat anchor to the nose. A Ringmaster is typical. You might get a tiny loss of power but that can be tolerated on most smaller models. When you get into some slightly larger airplanes, the balance is easier to maintain. The big thing here is replacing the .300" venturi with a .250: and then the next is he is using only 2% nitro. I'll bet the needle is less than a half turn from being closed. And if so, using the stock rear needle with it's blunt point and shallow taper ain't helping him very much. I see nothing wrong with changing things to improve the overall flight of the airplane, as long as you can put things back. It's the overall package that I am looking at and why I suggested he make several more flights to get a good baseline on settings before swapping out the muffler. If the engine is running good but the model won't turn and handle comfortably, it's not helping the over all package. Adding tail weight might be counter productive if the model is a little towards the heavy side. Smaller models cab be more likely to come out nose heavy. I don't think we are trying to recreate the infamous "Tucker Special Experiment" in this situation. He stated right off that the airplane "flies too good to put in the raffle" so I would try to avoid adding any excess weight if it's not really necessary. I have flown many airplanes, mine and others, with the LA .25 , with stock and tongue mufflers and just never saw that much difference in how it ran so I do what ever I think is necessary to get the best overall package.

    I'll leave this quote I read on another thread recently, I think you may recognize it:
     
   "  Obviously do as you wish, but you might at least consider that some of the rest of us know what we are doing, too.

    Brett "

   Type at you later,
   Dan McEntee

[Perry Rose]

I had to do it. Today I flew the plane with the tongue muffler. A lot more power and is controlable. I'm doing the one click per flight on the needle valve looking for the best setting. I'm launching at 12800 and the engine settles down to very fast 4 stroke breaking into 2 stroke around the circle. Good line tension overhead and should be at it's best in another click lean. I calculated the area of the 2030 muffler outlet and the holes in the tongue muffler and the 2030 muffler is half the area of the tongue. It's possible that my low nitro fuel is getting me the non standard runs everyone gets with the complete stock engine and muffler. I didn't buy this engine new nor do know where I got it. But I don't believe it has been modified internally only drilling the spray bar hole. I'm using the remote nva and stock spray bar with the .250 homemade venturi.

[Colin McRae]

I had to do it. Today I flew the plane with the tongue muffler. A lot more power and is controlable. I'm doing the one click per flight on the needle valve looking for the best setting. I'm launching at 12800 and the engine settles down to very fast 4 stroke breaking into 2 stroke around the circle. Good line tension overhead and should be at it's best in another click lean. I calculated the area of the 2030 muffler outlet and the holes in the tongue muffler and the 2030 muffler is half the area of the tongue. It's possible that my low nitro fuel is getting me the non standard runs everyone gets with the complete stock engine and muffler. I didn't buy this engine new nor do know where I got it. But I don't believe it has been modified internally only drilling the spray bar hole. I'm using the remote nva and stock spray bar with the .250 homemade venturi.

FYI, the OS 25LA stock muffler has an internal baffle, so the exhaust gases pass thru 2 restrictions. I'm not sure what a comparison of the outlet hole areas really offers. But the engine was 'designed' by OS to run and perform with the backpressure produced by the stock muffler.

I once tried a tongue muffler on my 25LA (on a relatively light Flite Streak model), and it went super lean (fast) in maneuvers. And it was a big difference that I did not like when it came to controlling the model. I went back to the stock muffler and did not experience the hard break in maneuvers. I personally like the engine to run at a relatively constant rpm no matter what I am doing in the air. Just my flying style.

To each his own. Bottom line is if you like the engine/model performance for your flying style that is all that really matters.

[Brett Buck]

\
I once tried a tongue muffler on my 25LA (on a relatively light Flite Streak model), and it went super lean (fast) in maneuvers.

  Just like the OP started with. That was the root of the problem, once that was solved there was a chance. I also agree  - matching the output hole area is not the issue, because the reason the stock muffler works and the tongue muffler will not is not about flow restriction.

Additonally, a lot of small, say, 3/32" holes whose area adds up to the same are as the single E2030 muffler outlet will be much more restrictive,  because of the viscosity. The outlet diameter .225x, and has an area of about 0.04 square inches. A 3/32 hole has an area of .0069 square inches and a 1/8 hole has an area of .0122 square inches.  That means you only need 6 3/32 holes or 4 1/8 holes to get the same area. That is far, far too restrictive, although it will certainly limit the RPM and power, it will also provide no control at all.

      Brett

[Perry Rose]

  I'm of the belief that nitro methane is very hard to come by in most areas of the world. If that is so designing bread and butter sport engines that need nitro wouldn't make good business sense. I know some back pressure helps but to make power an engine has to get air in and out as efficiently as possible that's why the baffle is in a box on the shelf. The baffle may help 'tune' the exhaust I can't say if it does or not but it's possible.
  Anyway with all the help and suggestions the engine is running fine on my homebrew/cheap fuel and that's the result I was hoping for.

[Paul Van Dort]

Hi Perry,

How is the tank mounted? If the uniflow exit in the tank is much more outboard than the spraybar, it will lean out after take off. Muffler pressure might help but it will make needling more sensitive.

Paul

[Brett Buck]

Hi Perry,

How is the tank mounted? If the uniflow exit in the tank is much more outboard than the spraybar, it will lean out after take off. Muffler pressure might help but it will make needling more sensitive.

Paul

    Muffler pressure makes it easier to needle, not more sensitive, because without you have to set it enough richer than you want to make up for the head variation. It's not enough pressure to get into the range where the needle opening is so small that any tiny variation has a big effect, it's just enough to mitigate the pressure head change, as long as you use a narrow enough tank.

     I note that if you tank is too wide, that is, more than about 1.5-1.75" from the engine lugs to the peak of the wedge or the outer edge, then you really may have a problem with it going too lean and speeding up after launch. I recommend an RC clunk tank like the Sullivan SS-4 with the flat side up against the profile fuselage, that is about 1.25 and has very little change from beginning to end as long as you use muffler pressure.

     I also note that you are probably right that the mixture probably goes leaner as you take off, but if it is running properly, the engine goes closer to a 4-stroke, because the while you have a leaner mixture, you also reduce the load, which has the opposite effect. That is almost always the case with stunt engines, if it is not, the problem is usually that the venturi is too big.   Of course exhaust tuning can alter it any way you want.

     Brett

[Perry Rose]

The tank is mounted against the fuselage side narrow side against the fuse. I use pressure all the time on everything. I changed from the Du-Bro 4 ounce tank to the Sullivan 4 ounce tank, which is smaller. I haven't flown the new combo yet. The engine is running well but has a slight loss of power in outside maneuvers. I adjusted the uniflow pipe with no effect so I changed tanks. I need 3 1/8 ounces for the pattern. I made a small metal tank but it's too long. I may cut a half inch off the tank. The plane is flying well so I'm fine tuning things.
 And Brett, by flat side do you mean the wider of the two sides?

[Brett Buck]

The tank is mounted against the fuselage side narrow side against the fuse. I use pressure all the time on everything. I changed from the Du-Bro 4 ounce tank to the Sullivan 4 ounce tank, which is smaller. I haven't flown the new combo yet. The engine is running well but has a slight loss of power in outside maneuvers. I adjusted the uniflow pipe with no effect so I changed tanks. I need 3 1/8 ounces for the pattern. I made a small metal tank but it's too long. I may cut a half inch off the tank. The plane is flying well so I'm fine tuning things.
 And Brett, by flat side do you mean the wider of the two sides?

    Yes , wide part up against the fuse side.  I think that is the simplest way to go. The other option is from Dirty Dan - mount it on the *inboard* side of the fuselage. Plenty of room and it is "stable" from a pressure standpoint (i.e. the pressure goes up a the speed goes up). In the traditional arrangement the system is only stable because even though the pressure goes down as the speed goes up, the speed going up also reduces the load on the engine, pushing it closer to a a 4stroke* - which sounds like it is "going richer" even though it isn't. But go too far, and then it the leaning out is more powerful than the load reduction, so it "runs away".

    That's at least part of the reason the stock muffler works and the tongue muffler doesn't, the load reaction with the stock muffler is much stronger and the muffler pressure goes up with RPM, which mitigates the pressure drop effects.

      Brett

*p.s. not just the "canonical" 20FP arrangement from the small engine experiments - more -or-less all successful stunt systems have the fuel supply pressure go down at launch and way down at various points in the pattern relative to the ground setting. That doesn't  stop them from doing things like "going rich" in places where the fuel supply pressure goes down, and "going lean" in places where the pressure goes up. The classic 4-2 break is a perfect example - starting a corner is like slamming on the brakes, this makes the fuel pressure goes WAY up as the acceleration shoves the fuel forward toward the engine. But the same slowing down also greatly increases the load on the enginem so instead of going rich, it "goes lean", breaking into a 2-stroke.

[Perry Rose]

Today, in the early morning ground fog,(the  park opens at 0700) I finally arrived at the set up that works on my design plane with the LA .25, almost stock muffler, 10 x 4 APC ,I broke the 9 x 4, sideways mounted Du-Bro fuel tank, cleaner engine cut, My fuel mix 2% nitro 22/23% oil 50/50 or thereabouts, 57 foot lines, 1.25 ounces on the tail, 1/4 inch tripler on the engine side, may not have been needed, remote NVA switched to normal O.S. NVA, again for a cleaner engine cut, with my homemade .250 venturi. I launched at 10,000rpm the engine picked up a bit and stayed at a steady 2 cycle rpm throughout the flight. What I could see of it.
  The bottom line after all 60 test flights (I document every flight) is that the engine needs the stock muffler most of all. Had I at least tried the stock muffler when Brett recommended it I would have saved a lot of hangar rash. At the start I had a decent looking new plane now it's raggedy as a soup sandwich. But it flys very well.

[wwwarbird]

 I'm stepping into this one way late Perry but your first mistake was modifying an FP or LA, they're fine right out of the box.

[Brett Buck]

At the start I had a decent looking new plane now it's raggedy as a soup sandwich. But it flys very well.

   Glad to hear it all worked out in the end! It really is a potent combination, and, you get a taste of what it is like to fly a pretty good piped system (like a 40VF) for a fraction of the cost and effort. I think you can see how it is different from traditional combinations - you make a mistake with a 4-2 break engine and a 10-6, and it more-or-less blows the entire maneuver before it recovers. With this, you make a mistake but it recovers right away.    Takes a whole different approach, if you blow one corner, you have to keep concentrating because you can still do the other 15 of them correctly.

    This is also why it makes such a good trainer.

     Brett

   

[Perry Rose]

I started building another.