Dave - I'll do my best to explain the symptoms:

YS 63 FZ, Powermaster 15/18, MAS 12x8

After starting up and pressurizing the tank, the engine will spool up to about 10K rpm, then (still at full throttle) rpm's drop to 8500 or so. engine does not sound good, sort of like it's not getting fuel. There is no smoke at all coming from the engine. On throttle back, engine quits.

There are some tiny bubbles coming from the joint where the cylinder head and crankcase meet.

The tank is holding pressure (after running, it is relieved through the vent line)

Things I've tried:
Reset valve clearances
New glow plug
Reset HS needle valve
Clean/inspect regulator and diaphragm

Any help would be greatly appreciated.


Bob

Bob Rob
I had a problem almost like yours. Found that I had the check valve in backwards. Check it.

Change the fuel to 20/20, go to a smaller prop or both. The problem is you don't have enough nitro to turn the 12x8 and the engine is overheating badly.

Keep doing what you are doing now, and the engine will be history.