Author Topic: causes of leanness (Read 1878 times)

Shorts,David · « **on:** June 08, 2022, 02:04:57 PM »

Generally speaking, and specifically speaking, what makes the engine go lean that I'm not considering?
To me, lean means too much air, too little fuel. My solution is open the needle. Well, it's not working.
SITUATION: 1. I'm rich on the ground, or even blubbery rich on the ground. As soon as I get airborn it starts going lean.
2. When holding the plane on the ground, I can start it blubbery rich. Then I point the nose up and it leans out. When I bring the nose back down it starts to go lean and stays lean even if I screw the needle several turns out. I can put the plane on a knife edge to bury the fuel pick up in fuel, but still stays lean.
3. once going lean, it still runs the tank empty, but just way too fast to fly.

Equipment: K&B .61. Just finished breaking it in on bench. Prop 12x6 apc and 13x5 wood (zinger?). Fuel, Power master 10/22. Muffler - pitts style, maybe tatone. Engine mounted sideways. Sulivan oval tank with fixed pickup.

Questions: Can a venturi be too big that fuel just can't keep up?
Does higher castor fuel keep an engine from going lean?
Are some engines just lousy?
Does underpropping make an engine go lean?

Thanks

Dan McEntee · « **Reply #1 on:** June 08, 2022, 07:26:21 PM »

Just so we know, what is the venturi ID? Is this a full fuselage model? Why have you mounted the engine in a side winder fashion? How is the tank oriented in the fuselage and to the engine? What kind of plug? There are things related to all these questions, but I would like to know the answers before making a comment. The K&B .61 isn't widely used but is a user friendly engine from what I have seen of them running. On a profile model, using a tank that is too wide and having to have the fuel run up against centrifugal will make an engine run lean in the air. You may be leaking a bit of air somewhere around the venturi that gets bigger as the engine heats up. Make sure the O-ring under the venturi is sealing correctly and also the spray bar in the venturi. Make sure the discharge hole in the spray bar is facing down and can not be seen by looking down the venturi bore. All of this works in conjunction with what the bore size of the venturi is and it will help to know that, plus the type of NVA.
Type at you later,
Dan McEntee

Shorts,David · « **Reply #2 on:** June 08, 2022, 11:17:44 PM »

Quote from: Dan McEntee on June 08, 2022, 07:26:21 PM

Just so we know, what is the venturi ID? Is this a full fuselage model? Why have you mounted the engine in a side winder fashion? How is the tank oriented in the fuselage and to the engine? What kind of plug? There are things related to all these questions, but I would like to know the answers before making a comment. The K&B .61 isn't widely used but is a user friendly engine from what I have seen of them running. On a profile model, using a tank that is too wide and having to have the fuel run up against centrifugal will make an engine run lean in the air. You may be leaking a bit of air somewhere around the venturi that gets bigger as the engine heats up. Make sure the O-ring under the venturi is sealing correctly and also the spray bar in the venturi. Make sure the discharge hole in the spray bar is facing down and can not be seen by looking down the venturi bore. All of this works in conjunction with what the bore size of the venturi is and it will help to know that, plus the type of NVA.
Type at you later,
Dan McEntee

Venturi and nva are stock. I don't have a micrometer to get the exact measurement.
The engine is sideways because the plane has cheek cowls, full fuselage, so just for appearance and not to load the engine and have to start it upside down.
The tank could be getting bubbles. I think I'll put in an inadequately small tank just so I can see if that's the rpoblem. Okay, I'll double check oringgs, I didn't think of that.
I thought maybe the engine was having trouble drawing fuel, but it does the same thing when not in the air.
Idk what plug is in it. It came with the engine I think. Should I try a colder plug? Which plugs are colder if so?
Thanks for the advice. I'll try some of this tomorrow in the garage.
I saw one kb 61 on a strega that ran great, so I gave it a try.

Brett Buck · « **Reply #3 on:** June 09, 2022, 12:31:41 AM »

Quote from: Shorts,David on June 08, 2022, 02:04:57 PM

Questions: Can a venturi be too big that fuel just can't keep up?

Absolutely - but apparently not in this case, since it is keeping up just fine at lower RPM. A smaller venturi might help because it reshapes the HP curve, rolling off the power at a lower RPM, which is the essence of your problem - you are running below the peak of the HP curve, which is unstable. As soon as it speeds up, it has more power at the higher RPM, so, it stays there. There may also be excessive drag in the fuel system due to a excessively small restriction/hole somewhere in the fuel system.

Quote

Does higher castor fuel keep an engine from going lean?

Generally not, if anything it makes it less able to draw fuel.

Quote

Are some engines just lousy?

Yes.

Quote

Does underpropping make an engine go lean?

Define "underpropping", but if you mean, too small, then no, too much prop will reduce the fuel draw and cause it to go leaner, and particular, too much pitch will induce you try to run it too slowly (to get a reasonable lap time), since you are on the unstable side of the RPM curve, the first chance it gets, it will take off to a higher RPM. A potential solution is to run less pitch, which will require more RPM, which can put you on the stable side of the HP curve. If it is too fast, you can also reduce the diameter to control the airspeed and require even more RPM. Thats how the 20FP works.

Without looking at your problem and doing some experiments, I hesitate to tell you exactly what to change to get it to work, but to forestall the ministrations of the Head Gasket Patrol, it is extremely unlikely to be that the engine is "overcompressed" and adding head gaskets is more likely to exacerbate the problem than to fix it.

My suggestions are:

Inspect the fuel system and in particular the inlet side of the spraybar for fuel passages that look too small or out of proportion to the fuel tubing, or any kinks or pinch points that might restrict the fuel flow.

Try conventional fuel, like Powermaster "Air" 10% or SIG Champion that has much less castor oil and therefore less viscosity that GMA fuel, same goal, to reduce the fuel flow restriction

Measure the venturi and spraybar dimensions and calculate the venturi choke area, report back, but if it is >0.024 square inches its probably too big, particularly if it has a fuel outlet that is flush with the inner wall of the venturi (i.e. just a hole in the side where the fuel comes out).

Run less pitch, like a 12-4.

Brett

GERALD WIMMER · « **Reply #4 on:** June 09, 2022, 03:55:42 AM »

Hello

My brother ran a number of K&B61's side-mounted with no run problems. He ran all caster and 5 % nitro with a 12x6 , only thing he found was a worn engine used a lot more fuel then a tight one and a new ring did not always bring back compression.
On fuel lines I almost gave up on a PAW19 that kept going lean in flight till I changed the tubing, as it was bending back and crimping in flight. With new thicker wall tubing that was rerouted the problem went away completely.

Regards Gerald.

Peter in Fairfax, VA · « **Reply #5 on:** June 09, 2022, 06:57:23 AM »

As far as venturi diameter, drill bits can give a very rough estimation. And the $20 for a General Tools dial caliper has been money well spent, as that purchase changed my technique in many types of craftsmanship. Everything from muffler hole spacing to wood thickness.

Question: What is the stock venturi like for a K&B .61? I thought they were delivered as R/C motors. Happen to know when a C/L version was produced?

One of the fellows in our club, Carl Cisneros of NVCL, runs the K&B .61 and likes it. He's on the forum and you might ask him.

thanks,

Peter

Dan McEntee · « **Reply #6 on:** June 09, 2022, 07:44:04 AM »

Make sure the back plate screws and head screws are tight. As to plug, any of the usual known good hot plugs. The one that is in the engine could be leaking. The oval tank with a fixed pick up has me wondering. If the tank is too low, it has to pull fuel uphill and even on the ground could run lean. From the information so far, I'm thinking it's in the fuel system. Switching to a different tank just to test is a good idea, but make sure the tank is high enough when mounted. In relation to the engine, pretend it's a profile model and make tank centerline about 3/8" higher that the engine centerline.
Type at you later,
Dan McEntee

Motorman · « **Reply #7 on:** June 09, 2022, 08:08:41 AM »

Most of the time these things are caused by the vent being too close to the pick up in the tank. Once the engine gets up any rpm, the air from the vent blankets the feed tube. The faster the engine goes the worse it gets.

Stock venturi could be made for a pressure system. Need to know more about the venturi size and configuration of the spraybar.

Motorman

Shorts,David · « **Reply #8 on:** June 09, 2022, 02:20:39 PM »

Okay, I'm starting round two today. For starters, venturi is between 11/32 and 23/64 on my drill bits. I'm trying tank three right now just to be sure. Still going lean. No air leaks in the nva. Haven't tried many of the suggestions yet. We'll see how long my back lasts then I'll report back.

Tim Wescott · « **Reply #9 on:** June 09, 2022, 02:30:25 PM »

Quote from: Shorts,David on June 09, 2022, 02:20:39 PM

Okay, I'm starting round two today. For starters, venturi is between 11/32 and 23/64 on my drill bits.

You need to take the amount that the spraybar blocks the venturi when computing area. If the spraybar is straight across, tell us how big it is -- this makes a big difference, which is why you don't want to go changing spraybar diameter on a nice stock OS FP or LA engine. If the fuel hole is coming out the side of the venturi, say so. If it's something in between (i.e., the spraybar is off center, or there's a nipple protruding into the venturi), show us a picture and try to get dimensions.

For a "conventional" venturi with a spraybar bunged through the middle, the area is roughly (0.78 * venturi diameter - spraybar diameter) * (venturi diameter). For no venturi at all, the area is just 0.78 * (venturi diameter)².

Tim Wescott · « **Reply #10 on:** June 09, 2022, 02:44:38 PM »

Quote from: Brett Buck on June 09, 2022, 12:31:41 AM

Measure the venturi and spraybar dimensions and calculate the venturi choke area, report back, but if it is >0.024 square inches its probably too big, particularly if it has a fuel outlet that is flush with the inner wall of the venturi (i.e. just a hole in the side where the fuel comes out).

With the smaller of the venturi sizes listed (11/32) and reasonable (no more than 5/32" / #6 screw size) spraybar bunged through the middle, I'm getting 0.038 inches².

@David: unless you've got a giant spraybar through the middle of that thing, you need a smaller venturi. If it's really that big -- you're saying that the hole in the ventur (not the outer diameter of the venturi) is almost 3/8 inches? If so -- goodgawd. That's sized for pull-your-arm-off speed runs, not stunt flyin'.

I've experienced exactly the effect that Brett's talking about -- with a 46LA and a Mystery Venturi that had to be blubbery rich to keep the plane slow enough, but would get on the step and run away part way through the flight. The solution was to use fine nylon mesh and pile layers of it on the venturi until I got the right balance of boost in the maneuvers and speed.

So, normally at this point I'd be recommending that you buy your sweetie some flowers that come wrapped in that super-fine nylon mesh that some does, hand over the flowers, and keep the mesh. (Nothing says "I care" more accurately than standing in a florist's shop and saying "I know you're allergic to those flowers, honey, but I'm really after the stuff they're wrapped in").

But if that venturi really is that ginormous, you're going to need a lot of layers of mesh to tone it down -- if you want to adjust with mesh and not by trying different venturi sizes, you want to start with something that's only a little bit too big. You could still do this, for the experiment -- but I think you want a smaller venturi.

Shorts,David · « **Reply #11 on:** June 09, 2022, 04:33:17 PM »

Thanks Tim, that makes sense. So the spray bar is straight across, centered with just a normal hole facing down into the engine. This is the stock KB CL .61 they've been selling since I took up CL. As near as I can measure, it's about 2.7mm OD, but that's with a plastic caliper.

I tried what Brett suggested with 5/16 powermaster. I also switched to a 2 oz tank. Everything worked perfectly. The needle was able to richen it to my hearts desire. Point it up to go lean, then point it back down and it'd go rich again. Then I switched back to my original Sulivan tank. When priming it, it was harder to draw fuel. Then when I ran it with the 5/16, I was able to keep it 4 stroking flat, and 2 stroke nose up. But it WOULD NOT go as rich with the big tank as with the 2oz tank.

Also, although this is a newish engine (I think they recommended 45 minute break in). But it sat on the shelf for maybe four years before I broke it in. What if the ring is shot? What would happen. It seems even when flooded a bit, it still turns over much easier than say on o.s. la 46. I've got no detectable leak in the tank or in the nva.

But, possibly I can try flying it again with the 5%.

TIM, I've tried the mesh before with pretty good results. If my problem is just too big of a venturi, then I'm glad to start meshing it up. It seems I'm guaranteed to nose over in the only dirt patch of the grass field so I like a little mesh on there.

Motorman · « **Reply #12 on:** June 09, 2022, 06:14:42 PM »

If you turn the spraybar so the hole is straight up then rotate it towards the back of the engine until it just goes out of sight then lock it down you will get more fuel draw.

You can stick a piece of tapered balsa in front of the spraybar and that will give you plenty of fuel draw. Less power too if you block it off too much.

Motorman

Peter in Fairfax, VA · « **Reply #13 on:** June 09, 2022, 06:26:09 PM »

That venturi size seems way too big.

Tim Wescott · « **Reply #14 on:** June 09, 2022, 06:44:33 PM »

I think your venturi is just too big. So yes -- pile on that mesh. See how much you need. Personally if I used more than five layers for that I'd probably fly and be happy -- while I was making or sourcing a smaller venturi.

If the "old" tank has problems drawing even when you're just priming, then that suggests a leak in the tank someplace, or a really bad restriction in there.

Does the Sullivan tank have one of those fancy sintered filtering clunks? If so -- maybe it's gotten dirty? Or do you have some really teeny fuel tubing in the Sullivan tank but not in the 2oz one?

Shorts,David · « **Reply #15 on:** June 09, 2022, 07:20:42 PM »

Okay, more data and results.
1. I'm still curious what happens if the ring is bad.
Tim, no the tank doesn't have a clunk. I did my best to get a solid pickup to the back corner, and then just put a vent somewhere and an overflow. So, not exactly a uniflow. Maybe both my first two tanks have leaks somewhere. I always blow into them to see if the air leaks out and call it good. I can blow pretty hard.

So, it ran good with propper needle response with the 2 oz tank, no mesh.
With the 8 oz sulivan I didn't get much draw and still went lean.
I used the 5%/18 oil powermaster and then it ran okay with the big tank.

*I used three ply mesh (5mm silk) with 5% and the big tank and it responded nicely. Good draw, was able to richen it too much. Had a nice break and good response pointing nose up and down. HOWEVER, the engine was incredibly hot afterward. Probably working too hard to breathe and only 18% oil? Does that sound reasonable. Other than the heat, this was like I hope an engine runs.
So I switched to 2 ply silk mesh and went back to 10/22 powermaster. Horrible. Here's what it did. If I richened it up, it would take about 10 seconds and then get so rich that it was about to die. I'd point the nose up and it would come up a little bit. Turn it a quarter turn leaner and in 10 more seconds be very lean again and with the nose down not go rich at all. Then I'd turn it a quarter rich. 10 seconds and then blubbering rich again. Did that the whole time. Some either it hates 10/22, or something to do with 3 ply versus 2 ply mesh.

Maybe I keep the 5% and add extra castor? Does a k&b need extra castor?
Maybe I keep 5% and one ply mesh. Maybe won't get so hot.
Maybe I go back to 3 ply mesh with 10/22 next.
Maybe I try a fourth tank. Not a bad idea I suppose.
Oh yeah, or try the 12*4.

Brett Buck · « **Reply #16 on:** June 09, 2022, 08:32:56 PM »

So, it is very clear that your venturi is FAR TOO LARGE to use for stunt. Using your given dimensions (23/32 and "2.7mm" {which I think is probably really 7/64}) I get 0.0567, which is WAY over the top. I note that its nearly twice as big as necessary, so you could get a lot closer by making a wedge of hard balsa and wedging it into the venturi between the wall and the spraybar to fill up the extra space.

Quote from: Shorts,David on June 09, 2022, 07:20:42 PM

*I used three ply mesh (5mm silk) with 5% and the big tank and it responded nicely. Good draw, was able to richen it too much. Had a nice break and good response pointing nose up and down. HOWEVER, the engine was incredibly hot afterward. Probably working too hard to breathe and only 18% oil? Does that sound reasonable.

No. 18% oil should be plenty if this is the newer K&B 61 with the screw-on head.

Quote

Other than the heat, this was like I hope an engine runs.
So I switched to 2 ply silk mesh and went back to 10/22 powermaster.
Maybe I keep the 5% and add extra castor? Does a k&b need extra castor?

No. I am not sure why you think you need a lot of castor oil, this is not a slug-piston engine.

Quote

Maybe I keep 5% and one ply mesh. Maybe won't get so hot.
Maybe I go back to 3 ply mesh with 10/22 next.
Maybe I try a fourth tank. Not a bad idea I suppose.
Oh yeah, or try the 12*4.

My interpretation - you have a VASTLY, ASTRONOMICALLY too large venturi, easily a factor of two too large. Putting on enough restriction got it *just good enough* to suck fuel in optimal conditions (conventional fuel with standard oil, not excess castor, short tubing runs (reducing the drag)) but still excessive so it is marginal in other situations (thick fuel and long tubing runs). So, for experiment's sake, remove the pantyhose or whatever, put the wedge in the venturi, and see what you get. I predict it will needle properly in all conditions with any of that fuel or any tank you have. Then fly it, and find whether there is any potential in the engine performance, then get a venturi/spraybar combination that gives you about 0.023-0.024 square inches of choke area, and use that. That will get you to a good starting point, then adjust as necessary in *small* increments (like .005" of venturi diameter) to get what you need.

Brett

Motorman · « **Reply #17 on:** June 09, 2022, 08:46:43 PM »

I think you're always going to have problems getting a setting until you get the right size venturi (.291"). You can adjust the airflow somewhat with mesh if you have basic fuel draw but trying to completely control the fuel signal with the choke is a bad situation.

A ringed engine can feel worn out because the ring gets more wall tension when the engine's running. If it starts without too much trouble then it's ok.

Motorman

Shorts,David · « **Reply #18 on:** June 10, 2022, 12:37:18 AM »

Quote from: Ty Marcucci on June 09, 2022, 10:39:47 PM

Check the fuel filter. I had a lean flight out of the blue and it was due to a filter getting plugged up with crap.It was a "crap trap" type filter.

Thanks, that one I had anticipated and checked my filter.

Dave Hull · « **Reply #19 on:** June 10, 2022, 12:42:20 AM »

We still don't know which engine David has. MECOA is currently selling the K&B .61 #6550 which is Pre-Twister. This has older metallurgy: aluminum piston, CI tension ring, and mild steel liner. I believe the venturi that comes with this engine has a .340" ID. It has a finned head, not the smooth anodized head with the two spanner holes of the Twister.

I have never had a Twister apart, but I believe these were ringless ABC engines.

So if the engine is the older aluminum and steel setup, I'd sure be using more than 18% oil and a bunch of it would be castor. If you don't like the viscosity of that mix, then fix the fuel system to improve the flow. The single biggest restriction in the standard fuel system is the filter--by far. If you have a clean tank and filter the fuel going in, you shouldn't have too much trouble with contamination.

I have seen two types of factory venturi's on these: a straight-sided OD, and a longer tapered OD. Not sure which (if either) is most suitable.

Letting an engine sit around will do nothing to harm the ring, unless you allow preservative oil to dry up and foul the ring groove. What will definitely harm the ring is running the engine too hot with fuel that has insufficient film strength. The heat will take the set out of the ring and you will be left with little to no compression. One good stonkin' hot run can make a previously good ring "go away." Been there on K&B .40s used for racing. But for stunt, and with an engine like the K&B .61, even being down on power a bit you probably still have plenty. So if it hand starts, you're probably fine. However, rings are still available from MECOA.

Good luck with your K und Beast,

Dave

Brett Buck · « **Reply #20 on:** June 10, 2022, 02:18:55 AM »

Quote from: Dave Hull on June 10, 2022, 12:42:20 AM

We still don't know which engine David has. MECOA is currently selling the K&B .61 #6550 which is Pre-Twister. This has older metallurgy: aluminum piston, CI tension ring, and mild steel liner. I believe the venturi that comes with this engine has a .340" ID. It has a finned head, not the smooth anodized head with the two spanner holes of the Twister.

I have never had a Twister apart, but I believe these were ringless ABC engines.

So if the engine is the older aluminum and steel setup, I'd sure be using more than 18% oil and a bunch of it would be castor. If you don't like the viscosity of that mix, then fix the fuel system to improve the flow. The single biggest restriction in the standard fuel system is the filter--by far. If you have a clean tank and filter the fuel going in, you shouldn't have too much trouble with contamination.

OK, as usual, these hypothetical and potential possible problems are trumped entirely *by running a venturi that it drastically too large!!*. It's entirely possible that there are also other issues, but his measurements and description of the behavior of the engine are perfectly consistent with each other. Until the venturi is corrected, there is no point in looking at these other issues, they are moot, because even if everything else is absolutely perfect, *it still won't run properly* with the existing venturi.

This is not subtle or some mystical flaw, it's perfectly straightforward, and the solution is pretty simple.

I also don't understand why absolutely normal and standard fuel should not work perfectly well without adding anything. You need lots of castor in iron piston running in steel liners, this is not that. Powermaster RC fuel is essentially identical to SIG Champion, I get exactly the same oil content from boil-downs, and at least since VP took over, the same power. The only difference is the tatering problem with SIG, that is a trace element or some sort of contamination in SIG. If it is the ABC version, you certainly don't need a lot of castor, although it won't hurt anything too much in the short term. If it is ringed, you absolutely do no want a lot of castor, all that will due it make it slowly lose compression until you devarnish it and run regular fuel.

We are making this WAY too complicated, we got the answer, and we won't know anything else useful about it until the venturi is corrected.

Brett

Dan McEntee · « **Reply #21 on:** June 10, 2022, 08:39:59 AM »

Jim Lee has venturi's for K&B .61s. I have gotten a few from him before but not sure what bubby hole they are in. I don't think any of the K&B/Veco .61'a I have were C/L versions stock from the factory, so can't help there with dimensions.

Type at you later,
Dan McEntee

kenneth cook · « **Reply #22 on:** June 11, 2022, 01:05:04 PM »

I use this K&B .61 on a 850 sq inch Ringmaster. My venturi is .295" with a .155" spraybar. I mainly run 50/50 Powermaster in this engine. I use a 12-5 wide blade for my smallest diameter prop. This engine has a sizeable counterweight on the crank. I noticed when I used a 4 pitch prop, it was shaking a bit so I stopped using it. This was with a new Zinger Pro series.

Just for the record, this isn't the easiest engine to take apart. The wrist pin needs to be removed through the screw plug on the rear of the case. Removing it is a pain in the balls. Reassembly is equally as difficult because all fits on this engine in the 3 examples I own are tight. Meaning, the liner to case fit is tight. The bearing fits to shafts are exceptionally tight and the bearing fit to case is tight. Therefore, removing the crank can remove the rear bearing due to it's fit. The bearing slides onto the shaft and the last 1/4" near the counterweight is slightly larger than the rest of the shaft.

Reassembly is equally troublesome, the piston needs to be slightly inserted into the cylinder during reassembly. I had to heat the case to enable the liner to slide down inside. You need to align the hole in the case with the rod and then insert the wrist pin. Don't insert too deep because the liner will not drop all the way down into position and if you do push it in too deep, it's difficult to get it back out.

Of course , everything I explained is meaningless to your posted question. I'm just letting you know if you decided to take this engine apart. I have replaced the rings in 2 of my examples. The cylinder liners are chrome and very durable. One thing I noted is that when I installed my Mecoa rings, they had a gap .004" on both engines. If you do change the ring, I highly suggest opting for a new wrist pin which comes with end pads as they do wear.

Brett Buck · « **Reply #23 on:** June 11, 2022, 03:49:49 PM »

Quote from: kenneth cook on June 11, 2022, 01:05:04 PM

I use this K&B .61 on a 850 sq inch Ringmaster. My venturi is .295" with a .155" spraybar. I mainly run 50/50 Powermaster in this engine. I use a 12-5 wide blade for my smallest diameter prop. This engine has a sizeable counterweight on the crank. I noticed when I used a 4 pitch prop, it was shaking a bit so I stopped using it. This was with a new Zinger Pro series.
<snip>
Of course , everything I explained is meaningless to your posted question. I'm just letting you know if you decided to take this engine apart. I have replaced the rings in 2 of my examples. The cylinder liners are chrome and very durable.

I disagree, the first paragraph illustrates the basic problem and shows a working system, and the second suggests that if you were inclined to take it apart, think twice, which is a highly valuable observation - *since it doesn't need to be taken apart in the first place*!

A lot of the other responses, while attempting to be helpful and illustrating *possible* but unlikely conditions, are like seeing a giant meteor headed toward Earth, building a rocket to shoot it down, and getting hung up on what color to paint it.

Brett

Shorts,David · « **Reply #24 on:** June 12, 2022, 04:48:10 PM »

Quote from: Brett Buck on June 11, 2022, 03:49:49 PM

are like seeing a giant meteor headed toward Earth, building a rocket to shoot it down, and getting hung up on what color to paint it.

Brett

Well that's easy, "Blue, no yellow..."

Tim Wescott · « **Reply #25 on:** June 12, 2022, 10:45:12 PM »

Quote from: Brett Buck on June 10, 2022, 02:18:55 AM

OK, as usual, these hypothetical and potential possible problems are trumped entirely *by running a venturi that it drastically too large!!*.

This is such an easy trap to fall into.

Fix the obvious problem first -- until you do that, any other behaviors are masked by that problem, and are essentially unknowns.

(And you should paint it gold and blue. Unless you're talking about the meteor -- I wouldn't bother painting that).

john e. holliday · « **Reply #26 on:** June 13, 2022, 06:52:53 AM »

This reminded me of a problem I had years ago flying a profile with a clunk tank. On the ground I don't know as I never ran it on the ground. It was fuel it, fire it up and go. The engine would four stroke/run rich until you forced the plane to do a loop. Then it would lean out and run the tank dry with out going over lean. The engine I think was a Super Tigre combat with a small venturi. J flew matches against a couple of club member winning each and every match. What was fun was watching them cover their winf with newspaper to have another match against me. It was one of those days I never had before. Never did figure out why as it was lean on launch.

By then way never take an engine apart unless you really know what you're doing.