I have a nitro trainer running on a OS Max FP .40. Before one of my flights last week, I "floored it" from idle and the engine just quit. I made the mistake of restarting it and just flying anyways. It happened again when I was still below 1 dumb high, and facing the opposite direction of the runway. I escaped with little damage though. Today, I went flying again. I never had this problem. The engine seemed to quickly accelerate from idle. The thing is, once flying the engine seemed to be making a noise like it wasn't running properly. It sounded rough-ish. I tried adjusting the idle, but just realized I had no idea what I was doing. Is this the problem or is it something else. Could the prop be out of balace? The engine seemed to vibrate a lot. Is this normal? I also had trouble starting it the first time.

Any help would be appreciated!<br type="_moz" />

Check for air leaks on the back cover and the base of the carb.

Also did you loose the small thin thrust washer?

Most O.S. engines use a very thin thrust washer, which is often lost by people who never realize it is gone.

The loss of the thrust washer lets the drive shaft move forward and back more than it should, which leads to strange noises, undue wear, and other problems.

No need for "flooring" these engines.

They should transition from low to high with no hesitation; however, the throttle stick shouldn't be moved suddenly.

I would check that washer that Opjose mentioned and the balance of the prop, besides all the bolts.

Opening the needle valve always helps at starts and for extra cooling and lubrication.

Study these links:

http://www.gettingairborne.com/engines.html

http://masportaviator.com/category/advanced/engines/

The OS .40 FP is an older OS engine that preceeded the OS .40 LA. Both engines utilize an air bleed carburetor that can be challenging to tune. Since the OS .40 FP is older I am guessing this is not the first time it has been run, so check all the screws and things mentioned above including the head bolts/screws. Based on your discription I would guess you had a rich mixture. Air leaks will cause a lean mixture. This of course could not be positively determined by me without actually watching and hearing the engine operate. I sudjest you find a local flyer to help you out in person for the best results. Inproper tuning can destroy the engine.