I have a 1966 Johnson 20 with low hours that I sold to a guy. It ran perfectly when I sold it (about 1½ months ago). He said that it ran well for a while, but then was having troubles. He replaced one coil, and then it was okay – for a while. Then he called and said that when he pulled the starter rope it would not start, and would build and build compression until only removing the plugs would allow it to turn over again.
I got it back, and was never able to replicate the ‘ultra compression’ problem.
1) I pulled the flywheel, checked coil alignment and wiring, checked the condensers, timed it with a degree wheel, adjusted the plug gap (appear to be new NGK’s), and tried it out.
2) It started and ran, but would not idle well. It appears to be missing badly.
3) When I accelerate to speed, it will stumble, and then runs like the wind. It runs perfectly at high speed.
4) It has great, uniform compression.
5) Adjusting the low speed jet appears to affect things, but if I lean it out enough to get higher idle RPM’s, it just quits.
6) I adjusted the carb advance roller so it just starts to kiss the ramp at the two marks as I advance the throttle.
HELP!