I know I am beating a dead horse here, but when I or someone else says *use stock parts*, it means to use the stock parts that came with the engine!  AGAIN, this weekend, a very knowledgable modeler came to me and said that they couldn't replicate my results with the 25LA (or in fact, the 20FP, either) and that neither had the sort of power I was claiming. So I take a look at the LA, and what do I see but yet another damn ST clone needle/spraybar instead of the superior and much smaller *stock* OS spraybar. 

   The stock ST spraybar is .157" in diameter. The *stock* spraybar is 3.5mm/.137". With the stock .257 venturi, you lose about 25-30% of your power, and THAT is why it won't go over 11.000 RPM on the ground and why your engine is wimpy!   Of course, there is no way to put a stock part back in the engine because the case and venturi had to be drilled out to get the larger spraybar to fit.

   So, OK, what is wrong with the 20FP?  At first blush, looks OK, clearly an OS needle/spraybar. Except on close examination, it's the old OS35S spraybar that is 0.155" in diameter, causing EXACTLY THE SAME ISSUE. With the SAME ISSUE THAT CANNOT BE FIXED AT THE FIELD BECAUSE THE CASE HAD ALSO BEEN DAMAGED BY DRILLING IT OUT.

   The solution in this case is to take a brand new 25LA out of a shoebox in the back of my van, modified it in *no way whatsoever*, bolt on an APC 9-4, fuel, attach battery, and flip prop. One run on the the ground. Instant nearly perfect runs, excellent power, very good competitive flights that later come in second in the contest over a NATs-level competitor.

   Later in the same contest - another very experienced modeler, another 25LA. This one has a chip muffler, and a 10-5 and would barely run in the air, eventually quitting inverted. I helpfully go get the airplane after the crash, flip it over, and guess what - yet ANOTHER ST spraybar. Guess we know why it needs a 10-5, and who knows how much more power was lost using a chip muffler. In this case, again, no way to put it back to normal even though I have stock venturis and stock spraybars right out of the package.

    The most practical fix to this issue - ASIDE FROM LEAVING THE DAMN THING ALONE SINCE IT WAS FAR BETTER BEFORE IT WAS "IMPROVED" - is to drill out the venturi to recover the lost choke area. To match it up, you need a .275 venturi bore with an ST or the old OS35 spraybar. Maybe I should start bringing a Letter I-sized hand reamer to contests. A different solution is to sleeve a *stock* OS 20-40FP spraybar to fit the oversize hole that was erroneously drilled in the case. This is pretty tricky because you have to make the sleeves long enough to engage in the case and the venturi, but not so long that the intrude on the bore of the venturi.

  BTW, as a general rule, the OS spraybar is *superior* to the ST or ST-clone types. The needle in the OS spraybar is very nicely supported on the inner bore of the spraybar, and the needle itself is pretty stiff. The ST and ST-Clones support the needle only at the pinch end of the collet and it otherwise hangs from the threads like a tuning fork. This was notorious i the good old days for problems, and you want to run the collet as tight as it can be and still be able to turn it. The needle itself is also thin and very pointy, meaning that if the point is slightly different, bent ,etc. (and no two were ever really alike) you have no idea what the effect might be. The PA and RO-Jett needles are much superior to the ST, if nothing else, because they have teflon/nylon compression fittings for the seal, which also damps vibrations nicely.

   The purported advantage of the ST and similar needles is that they are infinitely adjustable. That is at best a double-edged sword, for stunt at least, because while you can get any setting, you can also easily make a change in the needle too small to be of any use. A click-type needle forces you to make a distinct change, and can be repeated. If there was some way to put an OS needle in my RO-Jett, I probably would.

  Bottom line - just run the damn engine (any of them) as they come, and only modify them if you have identified a genuine problem that requires a solution!

    Brett

More importantly do you have anymore 25's in that shoebox? 

Sounds like there is $$$ to be made in the "spraybar sleeving" business.

Phil, why is it a PITA to convert the RC engines?

I think that OS uses something like Loctite on the two screws that hold the carb in but once undone, the conversion only requires the correct venturi and factory 3.5mm dia NVA that Brett talks about. No drills required, just the correct size spanners. The hex on the OS spraybar and the nut are 5.5mm AF but I couldn't find 5.5mm sockets here in Oz so I used 7/32"AF. I've just found that 5.5mm AF is a size used on 1:10 cars so maybe I can get a couple of those.

Phil, why is it a PITA to convert the RC engines?

I think that OS uses something like Loctite on the two screws that hold the carb in but once undone, the conversion only requires the correct venturi and factory 3.5mm dia NVA that Brett talks about. No drills required, just the correct size spanners. The hex on the OS spraybar and the nut are 5.5mm AF but I couldn't find 5.5mm sockets here in Oz so I used 7/32"AF. I've just found that 5.5mm AF is a size used on 1:10 cars so maybe I can get a couple of those.

I could not get parts.  Now this was right when the LA went discontinued, so there may have been a run on the parts needed.

The actual labor is trivial.  Change the muffler on the iron lunged FP to the E2030 muffler (the ABN version supposedly shipped with this muffler) swap the carburetor to the venturi, which is 2 screws to remove (USE HEAT GUN!) and replaced with the NVA spray bar or remote NVA nozzle.  The spray bar is arguably superior to the remote NVA as the new plastic back is fully molded and in the way in all positions.

I ended up going through
http://rcjapan.net/
and had to wait over 6 weeks before they had my order together to ship.  At least with the Yen to USD the price delivered ended up favorable.  I ordered enough parts to convert the 3 FP20 engines I have.  I only converted one so far.  Yes it is an iron cylinder, and runs very nicely.  Better than I can fly it.

The two LA25's I have proved how much the plastic backs aggravate.  I ended up making aluminum NVA guards to capture in the engine mounting bolts since the remote needle hangs out in space with not much protection against an inverted pancake on a profile.

I am "engined up" enough I hope that by the time I learn to fly well enough there will be other, proven options, or I'll have a good enough grasp on electrickery and timers.  

Phil

I could not get parts.  Now this was right when the LA went discontinued, so there may have been a run on the parts needed.

The actual labor is trivial.  Change the muffler on the iron lunged FP to the E2030 muffler (the ABN version supposedly shipped with this muffler) swap the carburetor to the venturi, which is 2 screws to remove (USE HEAT GUN!) and replaced with the NVA spray bar or remote NVA nozzle.  The spray bar is arguably superior to the remote NVA as the new plastic back is fully molded and in the way in all positions.

I ended up going through
http://rcjapan.net/
and had to wait over 6 weeks before they had my order together to ship.  At least with the Yen to USD the price delivered ended up favorable.  I ordered enough parts to convert the 3 FP20 engines I have.  I only converted one so far.  Yes it is an iron cylinder, and runs very nicely.  Better than I can fly it.

The two LA25's I have proved how much the plastic backs aggravate.  I ended up making aluminum NVA guards to capture in the engine mounting bolts since the remote needle hangs out in space with not much protection against an inverted pancake on a profile.

I am "engined up" enough I hope that by the time I learn to fly well enough there will be other, proven options, or I'll have a good enough grasp on electrickery and timers.  

Phil

   These are the various parts for the front and rear-needle engine. The venturi is the same for the OS20FP, 25FP, and the 25LA. The front needle and spraybar assembly is the same for the 20/25FP and 25LA front needle. The rear cover plate assembly and front nozzle are for the 25LA, but I think the nozzle is the same for the 20/25FP rear-needle versions. I don't know about the bracket for the 20/25FP rear needle version.  I saw several likely candidates in the parts list but didn't try to track them down. The rear needle metering section for the 20/25FP is almost certainly in there. If you have an OS20/25FP with the stock RC carb, the core of the carb where the needle is is exactly the same as the rear needle/metering block on the 20/25FP RN. Just unscrew the spray bar from the RC carb, and you have the metering block and needle.

   All show as available in the Tower parts list.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCR49&P=SM
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCW99&P=ML

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMU30&P=7

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCF88&P=7

I am glad to see parts support is available now.  This is where I started and there were no parts to be had when I was trying to get parts.

Apparently I had a classic "Bad Experience".

Phil

    It's not that easy to find in the Tower parts lists. I tried searching with their search feature and didn't find anything. I had to go down by category and make educated guesses on where to look.

     Brett

the LA .25 is really an interesting study to me. Like they say on King of the Hill...."the boy ain't right"
I use the engine in a proto speed event so trying to get performance out of "sluggo the engine" is not as simple as it might be.
I can tell you that they really like to breathe and will reward you with performance when they do. I have used the plastic backplate and nva with no ill effects. I have gone so far as to make the assembly work with an ST nva in the remote housing.....about the same...needled a bit better. Stock with a large venturi will give you pretty good power.

K

" Brett, you say for the fat spraybar's diameter, use a .257" bore, and Randy, you say .281. Not much difference, but do you guys think that could be just due to the difference between our geographic areas, GA/SC compared to California? Or personal preference?

Rusty "


For the larger diameter spray bar  use the  281 venturi
for the small diameter 20 size spray bar use the 255 or 257 venturi  , that way they act the same

This is what you want, is to install the equivalent to each other, go the other way and you seriously choke down the S venturi  and  have  WAY to large of open area on the  L venturie

The OS venturies that fits the  OS 35 40 FP, 25 , 40 , 46 LA   are nominal  S 255   and  L 281 ,  these are the two we are talking about
A caveat I have seen several  290 and slightly above come thru in STOCK 40 46 LA, just a few , but  they were larger

Randy

OK, now that I have obtained a NIB OS 20FP ABN and the correct OS venturi and NVA, how do I get the RC carb out of the case? I have tried heat and have almost ruined the Phillips head screws. Is there another way to remove the screws besides heat? Got a Flite Streak ARF waiting for this baby.

OK, now that I have obtained a NIB OS 20FP ABN and the correct OS venturi and NVA, how do I get the RC carb out of the case? I have tried heat and have almost ruined the Phillips head screws. Is there another way to remove the screws besides heat? Got a Flite Streak ARF waiting for this baby.

A screwdriver?

A properly sized screwdriver.  Cross-head screws like that need an exact fit to the screwdriver to work correctly, and the OS engines use JIS screws.  I'm channeling Brett here, but I can't do it well enough to tell you which size to use -- I just have a collection of screwdrivers and I use the one that fits exactly with no wobble.

Even if you've already munged the heads greatly, the correct screwdriver will still take them out.  Failing that, a Dremel Dangerous Disk will make a slot that'll let you take them out with a regular flat screwdriver -- but it's better and safer to use the correct screwdriver.

OK, now that I have obtained a NIB OS 20FP ABN and the correct OS venturi and NVA, how do I get the RC carb out of the case? I have tried heat and have almost ruined the Phillips head screws. Is there another way to remove the screws besides heat? Got a Flite Streak ARF waiting for this baby.

    I believe they use something like Loctite on the threads. But note the little dimples on the heads of the screws. That indicates that they are not Phillips but Japanese standard screws.  You need a proper screwdriver. Get the Hozan JIS screwdrivers. They work better than conventional cross-head drivers in Japanese standard screws. Conventional Phillips drivers from the US will usually be difficult to use at best, or damage the slots. The JIS drivers work better in conventional Phillips, too. With a proper fit, the Japanese drivers work better than Allen head screws.

    If you are careful you can grind a conventional Phillips to work by making the point a bit less sharp, and leaving hard sharp edges on the individual flutes. I would guess a JIS driver would still get your screws out even with damage because the standard Phillips just knocked the points of the cross off right in the middle, and the proper driver would engage the entire depth of each slot all the way to the end. Of course, at this point, you could do what we all used to do with motorcycle JIS screws - grab the outside of the heads with Vise-Grips and twist them out. You aren't going to use them any more anyway.

    The other factor is that people tend to use the wrong size drivers, usually too small. The right one for the screws you are trying is probably a #2, which looks way too big. The biggest size that will fit is the right size.

   By the way, don't toss the carburetor. The core of the carb was formerly sold as and can be used as a remote needle system.

    Brett
    

OK, now that I have obtained a NIB OS 20FP ABN and the correct OS venturi and NVA, how do I get the RC carb out of the case? I have tried heat and have almost ruined the Phillips head screws. Is there another way to remove the screws besides heat? Got a Flite Streak ARF waiting for this baby.

you didnt by chance own half the British Motorcycles in Newzealand in the late 60s . DID YOU . !

If you can get the end of an unbutched VICEGRIP on the swine without fouling the case , Free It 1/4 turn , and use a screwdiver THAT FITS .

Super Tigre HEEAD BOLTS require ' Grinding Up ' or making ( Like they taught in 4th form metalwork ) a screwdiver with parrallell flanks .

Back on Subject . Half the MECHANICS that worked on pommy bikes were hopeless  , it wasnt untill a few engineers and aircraft mechanics got hold of them , that they started Running Properly .
After Being ABUSED during ' run in ' , and maladjusted and neglected during warrenty .

So Put Away that hammer & Chisel and leave the Liner Alone .

Brreak in , or Non Abuse in its early life , will let the engine settle in properly , for long life & good running . The Hotter months arnt reallly the time to get that new engine out of the box & bolt it in .
A winter ; Bed in & Test ' regime would be a worthy enterprise . Unless your in Alaska . 

The Japanese do not refer to these cross screws that way. They call them PLUS and the blade style as MINUS. Learned this working directly with jap service people.

But the point is the  Japanese drivers  work, and most of the other just tear out the bolt heads , as  Brett  has stressed many many times, they need the right tool,  I have posted where to get a nice  NON expensives set, and  I will try to find the post and repost it.  OS  puts screws in very tight, and this is a problem that we all have, the proper tool  makes it easy.
I have ran into the same problem for decades with all the  OS motors.

Randy   ps   I use  the bottom  on, it is a  very good set with several tips
https://www.ebay.com/itm/TOPTUL-FSIA0802G-2-Long-2-Phillips-Screwdriver-Bits-10-pcs-JIS-Compatible/123035754656?hash=item1ca580a0a0:g:wSsAAOSwuMZZI8rz

https://www.ebay.com/itm/Ball-Grip-Screwdrivers-Set-Metric-Japanese-Motorcycle-Drivers-JIS-standard/173135624949?hash=item284faffaf5:g:nO8AAOSwE7JadCM1