I have a moki 180 with 10 hours running time, just mounted into a new model.
I have a new vp30 perry regulating pump.
I have a fuel tank 10" from pump.
I have the pump 3" from the engine.
I have a new moki glow plug.
I have a 18x10 prop.
I have GX-5 fuel (no nitro, high castor content).
I have the top needle set around 2.5-3.5 turns out for starting.
I have the idle disk set at about 4 degrees lean from the neutral.
I have problems..


The engine starts and idles well. The engine transitions from idle to full throttle immediately. However, if I keep the throttle fully open for a few seconds the rpm drops from ~7500 to ~5000 where it remains for a few seconds then goes back to ~7500 and the high/low RPM cycle repeats. Typically the engine sits at each rpm for around 3 seconds.

I've tried different idle and top needle settings nothing seems to help.
Thought top end was lean, tried richening to no avail.
There are no air bubbles in the fuel.



Any ideas?