1971 johnson 25hp idles at start position

[Caleb Teague]

Electric start. This motor sat for 3 years before I got it. I poured a teaspoon of oil into the cylinders before starting it, and cleaned the carb (no rebuild). Compression is at least even between cylinders and is fairly strong, moderately ifficult to pull the cord. But she fires up every single time. The engine works excellently at full throttle but idle is shaky and not right. The low speed passageways in the carb are well clear and cleaned. The adjustment screw is adjusted, any more clockwise and she sneezes. I've read the engine is probably sucking air from somewhere else and the upper crankcase seal is likely the culprit.

Is there a way to definitely test this? Also, when replacing this, do I need any special tools or knowledge for the timing system?

Thank you for any input you can give. It is greatly appreciated.

 

[flyingscott]

Did.you soak the carb? Did you blow compressed air through all the passages? I.would try properly cleaning the carb before anything. And use a quality rebuild kit.

 

[jimmbo]

If the crankcase seal is leaking, sometimes running a 24:1 gas oil mix gets a bit more oil on the crank and seal, enough to reduce the leakage, and the engine runs better. Remove the flywheel and look for oil seepage/leakage on the crankshaft.
What do the plugs look like?
Soaking a carb, and blowing out with compressair is no guarantee that the idle passages are clear. The welsh type plugs need to removed to ensure there is no gum/dirt/varnish is hiding in there

 

[racerone]

Upper crankshaft seal leaking would put oil all over the breaker points.----Pull the flywheel to inspect that.-----Perhaps throttle plate is opening too early.-----The "start " marking is just a guide, and some one may have the gear off by one tooth.----Thermostat in place and working properly ?