ORIGINAL: ScottMcM
I have been tinkering off and on with this engine, and still can't get any decent rpm's out of it. With a 15x6 apc propeller, omega 15%, I get 7000rpm, with 10% omega, I get 6500rpm, and with 30%, I get 6800rpm. It will idle down to around 2000rpm with the 15 or 30%, but it doesn't idle well with the 10%. There is a huge amount of ''slobber'' coming out of the crankcase nipple. I have checked and reset the valves, checked and reset the timing, new glowplug....any ideas, or am I expecting too much from this old warhorse? It idles and transitions great, and runs smoothly throughout the rpm range. I was a little surprised at the drop in rpm's using the 30% fuel. I expected it with the 10%, but not the 30%.
If you are getting excessive slobber out of the crankcase vent nipple, the idle is crappy, chances are your engine's compression is down (bad ring). I would replace the piston ring and break it in again. Just run it a bit rich with the new piston ring and don't let it get very hot for a while. All of this can be done in the air.
The only glow plug that I would use in this engine are the OS Type F. Get a new one and install it AFTER break-in. Don't worry about the idle and transition to full throttle until after the ring has seated. Then install the new glow plug and be patient. Unlike some two-strokes, making very large changes in the needle settings on this engine can lead you to missing the "sweet spot" that you are searching for. Four-stroke model engines are a different experience from the two-strokes. Good luck. You have a great engine.
Ed Cregger