I am rather new to flying (4 months) and I have a super stick 40 with an OS 46 AX installed. The OS was also used on my previous trainer. I had no problem with the motor until three flights back. The engine just lost rpm after an inverted flight. It didn't die at first but after working the throttle to regain rpm I eventually had my very first dead stick and crashed my plane. After a few days of repairs I took her up again, and again the engine just suddenly lost rpm. This time I landed with no damage. I might just add that the engine runs real good on the ground. I adjusted the low and high needles by the book, leak tested the tank, replaced the brass pipes in the tank, cleaned the carb etc. but nothing helped. The engine still starts good, picks up rpm but then takes a second or two to peak. I asked all the gurus at our club who all tried to dial the engine but there is no progress. What can I do??? One guy suggested that my fuel may have collected moisture (due to our summer rainy season). I must admit that the fuel I have is less than fresh. It is about 5 weeks old. I also fly only 20% oil with no nitro.

I am really lost here. Please help!

Try the fuel first. Get some good 10% - 15% nitro fuel. There are several on the market. Wildcat and Omega are my favorites, but there are others as well. If you have a fuel filter in the line between the tank and the carb, get rid of it and filter the fuel between the fuel jug and the tank. If that does not do it try a new RC long glow plug. If that does not work, I suggest you send it in for service.

I'll have to try the fuel. I have filter on the line between the bottle and the tank. I don't have a filter between the carb and the tank. I tried a new glow (no 8) aswell.

What type of clunk line do you have. If the engine only sags when inverted, then I'm guessing the clunk line is too stiff to fall easily to the "top" of the tank when inverted. The engine starves for fuel, goes lean and loses rpm.

If your clunk line is a little too long, it may also be hanging up against the back of the tank.

Have you tried inverted when you first take off, ie. when the tank is full?
Dennis-

I have a soft silicone tube as a clunk line (tried two different tubings). The clung also moves freely. I have checked this with a full tank with wings off and I can see the clunk moving freely inside. It drops very quickly when the plane is turned upside down. The very first inverted flight (when I first crashed it) was with a 3/4 tank. It was not full.

You stated the engine died when inverted with 3/4 of a tank. This leads me to believe you MAY have an air leak somewhere.

I suggest doing/trying the following:

1. Replace ALL the fuel lines on the engine and in the fuel sustem, including the line from the clunk.

2. Check the o-rings on the needle valve - replace if they look worn or are hard or cracked.

3. Make sure the back plate and carb are seated and not leaking air. Sometimes the engine will run good on the ground, but the vibration in the air (it is a slightly different type of vibration ) will allow air to leak past the back plate and/or carb. A little bit of silicone cures that problem.

4. I know you said the glow plug was new, but check it anyway. It should glow a BRIGHT orange/red AND ALL THE COILS should be glowing. The OS #8 is an excellent plug for the 46 AX.

5. Try a different fuel - perhaps 10% nitro. Someone at the field should let you try a tank full of theirs.

6. Make sure your muffler to fuel tank connection is tight.

7. You said "The engine still starts good, picks up rpm but then takes a second or two to peak. "
This IMPLIES that your transition (idle/high speed ) adjustments may be off a little. The engine should go from idle to peak in a smooth manner, with no hesitation, coughing or stumbling.

You need to peak the engine, THEN BACK OFF ABOUT 1/8 TURN (about 300 - 400 rpm ). The engine unloads in the air and if you have it peaked on the ground you may be leaning it out in the air, especially if doing any type of manuvers.

I have found that the best way to check this out is:

After the engine is adjusted, with the engine at full throttle, pick the plane up and point it nose up and hold it there for about 10 seconds. The engine should stay at the same rpm. If it changes rpms the high speed adjustment if off.

One possiblity is vibration-induced fuel-foaming. This means that the engine's vibrations are agitating air into the fuel when the model's in flight. This will cause the mixture to go lean. You'll have to either add or remove padding around the fuel tank to reduce or eliminate it. To liitle padding give no isolation, and too much means that the padding's compressed enough to not do its job.

You may also want to check to see if the tank vents properly if the engine only has problems when you go inverted. Without good venting, a vacuum builds up in the tank as fuel's drawn and prevents the fuel from being drawn into the engine. The engine goes lean and can die.

I'll back up what Bax said. With normal venting (even with muffler pressure) an engine always runs leaner when inverted so if you're tuning close to peak then it'll go too lean inverted.

After reading a bunch of posts on engines leaning out when nose is pointed up, blocking one outlet tube on Pitts mufflers to increase pressure, etc. etc. , I found that the pressure nipple on my Tatone Pitts Muffler was loose causing a reduction in already marginal muffler pressure. I'm hoping that tightening the pressure nipple plus full closing off one outlet tube will give my ASP.40 more consistent running in level flight versus lean-out in nose up and inverted positions.

It seems that Pitts style mufflers for scale models are a big source of problems for fuel pressure and even running