Ok, this is starting to drive me insane. I have a "newer" OS .46LA Engine on my trainer. Whenever I am at full power, the engine starts surging. It will constantly change RPM. It doesn't ever show signs of quitting, just problems running at full throttle. I replaced the engine fuel supply system, and I'm still having the same problems. I also borrowed a tank of gas from another club member, and the problem continued. Does anyone have any ideas what is going on?

Thanks,
Matt

Airleak maybe? Or a servo oscillating a little. I look for airleaks with wd40. Spray around the usual places, carb base, HS needle, back plate, head. Run the engine full throttle, if you find a leak, the rpm will sag.
Edwin

If you have replaced the Fuel System - most of the problem areas have been eliminated - in this process did you also replace ALL of the fuel lines?

Next; have you cleaned the carburator and needle valve? []

These items usually cause poor fuel flow that give hard starting or air in the lines which gives you a lean run - but they all need to be looked at. [X(]

Surging of the engine can also be caused by a motor mount that is loose and causes the engine to vibrate - check all mounting bolts on both the engine and from the engine to the firewall. Locknuts are a wonderful thing.

Good Luck

Might well be fuel foaming. Often caused by engine vibration. Try balencing the prop. Can you insulate the tank with foam?

Some people also say that they can add something to the fuel to stop foaming but fixing the cause is better.

I've heard about that additive. It was armoral, just a few drops per gallon. Just speculation. Never tried it myself and dont know of anybody that actually tried it either. I wouldnt do it.
Edwin

Run it full throttle, see any air bubbles between tank and needle valve? Yes, then a foaming issue most likely, pad the tank. If you only see the air bubbles between the needle valve and carb, then your needle valve assembaly is leaking, tighten it up, seal it up, and/or move it off the back plate (it can hang in space, or screw it to firewall or something. Often when I've seen this it's the valve, cut a narrow piece of full tubing and slip over the needle and then screw it into the asm. (O ring is better if you can find the right size at ACE).
All in all, I'd bet it's the high speen needle valve asm. I've seen this many times.

You say you replaced the fuel lines. Does that include those inside the tank? Sounds to me like you have a leak in the line in tank or the clunk is stuck up in front, OR you are trying to supply fuel through the vent not the fuel line in tank. It happens sometimes we hook up wrong line to motor. I use red fuel line for supply, green for vent (pressure line) natural for filler line. You only need three lines when motor is cowled. Unless you use an auto fill valve.

I'll go with the servo...
look in the carb intake is it oscillating as well?

My Evo.46's likes to do that and I've always have solved the problem by landing the plane asap and adjusting the high end two to three clicks richer... depending how lean the Needle might be. Barometric Pressure, humidity and temp has a big role on how well our engines run, that is why I always re-adjust my High End before every flight. It drives my club crazy and they complain that I adjust my engine too much, but when I do it my way I have less Dead Sticks. [sm=75_75.gif]

I flew my Goldberg ARF 62 Skylane at a airshow in Palermo, NY on July 26th just before a nasty thunderstorm came rolling in. It was really embarrassing when my engine started surging. I flew the plane two days earlier and had no problems... but yet again, it was a cool dry day, not the hot and humid day at the airshow.

A nasty way of finding leaks ( Which is the hard way ) is to run the idle up on your engine and lift the plane nose up vertically. I've had Glow Fuel Showers before when I suspected a fuel or air leak. [:@]

The O-ring idea sounds like a good idea. Just be careful with your fuel lines when you re-fuel and etc. The fuel lines become weak after a while and can tear or break. It's happened to me countless of times. I always carry extra fuel tubing with me in the starter box.

I don't recommend putting any additives in your glow fuel, you risk killing your engine and or plane with a nasty Dead Stick plus O.S. and Evo doesn't endorse such stunts either. And yes, check to see if your fuel is foaming in your fuel lines. If so then I second the " Re-ballance your prop " idea and try to reduce your vibration any way you can to the airplane.

Hope I helped

Luftwaffe Oberst
Radio Aero Modelers Club
Pulaski, NY

Supporter of RedNeck R/C Fulton, NY