My os 25 keeps dying on me at full throttle when flying it. It seems to run fine on the ground, but in the air at level flight, she will eventually deadstick on me. It takes about 5 minutes for it to start acting up. Its like its changing the tune while flying. I noticed the little prong isn't real tight against the HSN. Could it be moving from vibration while I am flying her. It sounds like it starts to bog just before it dies, so does that mean its going to a rich condition? It's getting annoying, I haven't had a landing with it yet where the engine is still running.

its alsways a good idea to tighten the little "prong" against hte HSN for extra security, sounds to me like it may be running lean.

you should try tuning it so that its running rich on teh ground (but still gives enough power to fly reliably) because high up in the air it will run leaner, and thats probably where your problems are starting.

tune about 3 clicks rich on the ground and see how you go .

the fact that it takes 5 minutes to start acting up doesnt sound like a glow plug or fuel system fault... i could be wrong though

Try tuning a click or 2 richer than you are. Sounds like the engine goes lean as the fuel level drops.

Also, be sure the muffler pressure line is hooked up and clear of blockages or kinks.

Be sure the clunk line in the tank is not punctured (replace it for good measure). If there's a pinhole in the line inside the tank, the engine will run well until that pinhole is uncovered, then it'll begin to suck some air and go lean.

Good luck,

J

Check the clunk to be sure it's not wedged up towards the front of the tank. Sometimes a "hard landing" will wedge the clunk in the front corner of the tank. When the tank is full, it flies fine, but when the tank empties out a little, the clunk doesn't always find the fuel, and it will die out on you. If you typically got 10-12 minute on a tank, and now you're getting ~5 minutes before your engine dies, that's a common symptom of a wedge fuel tank clunk.

I guess I'll pull out the clunk system. This plane was assembled when it was given to me so I don't know how the stuff in their is. I bet since it was old the lines inside have small splits or something.

Pulling out the clunk lines might not be necassary. Most times, a stuck clunk can be freed by shaking or bumping the fuse (in a sturdy area of the plane). If it works, you should be able to hear it "clunking" when shaking the fuse.

There is an outside chance of fuel foaming. If the engine vibrates beyond a certain point [for any reason] or if the fuel tank isn't padded well enough, this can cause a lean condition. You can usually spot this problem on the ground.

You don't say if it is in a cowled instalation, if so it may be overheating, just something else to watch.

Cheers

Pulled the tank out and it looks like it was installed with too long of a clunk line. I suspect that it may have been sticking at the top of the tank after an inverted maneuver. I shortened it and will retune and fly on Wednesday night.

Yes this can and does occur on occassion. Remove the needle and and bend the detent spring(s) in, then carefully reinstall the needle.

Your engine is going lean in flight and folks have already given you most of the common reasons and cures. Another to ad to the list is a tank that is to low in the fuselage will give similar symptoms. The tanks center should be level with the spraybar (jet) in the carb, no matter if the engine is mounted upright, side ways or inverted the tank needs to center on the spraybar.

Here are another couple of hints. When returning an old airplane to flight If the fuel tank has been assembled then don,t use it. Replace with a new tank always. Coventional bung plug type tanks have been assembled for a long time even if they have never seen fuel will be almost impossible to reseal if you remove the plug to check clunks etc.

Also if I may the very best type tank to use in most conventional glow setups are the Hayes tanks:

http://www3.towerhobbies.com/cgi-bin...?&I=LXK829&P=7

This is the best tank possible. it does not use a rubber bung that will deform but instead a hard plastic plug with an O ring and it seals beautifully, but more important the plug can be removed countless times for years and still seal on replacement. Only the clunk line goes through the plug. Far easier to assemble and far more reliable over great periods of time.