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