1971 Johnson 20 hp smokes at idle.

[Bearcamp]

I have a 1971 johnson 20 hp with good compression (about 115 in each cylinder) Runs great but at idle it seems to smoke so much. New plugs, points, condensers and I'm running the oil, gas mixture at 50 to 1. I thought maybe head gasket, but good compression. Sometimes when it idles for a minute or two I throttle it up and seems like 1 cylinder misses til it gets cleaned out. Or do they idle like that, sorta rough. Even tried adjusting the carb adjustment screw and helps some. What about float level too high?

 

[alcan]

Re: 1971 Johnson 20 hp smokes at idle.

Hi Bearcamp<br />It sounds like you are on the right track. Check float for proper funtion and level. If all is well, lean the low speed needle some more. Remember the throtle valve has to be fully closed in order to get an accurate adjustment with the low speed needle. Also make sure the idle stop is backed out. Sometimes the low speed needle gets set too lean or is pluged, so the operator tries to compensate by increasing the idle stop screw. This opens the throtle a bit, allowing the engine to get fuel from the main nozzle or high speed circut. The effect is an over rich air/fuel mix and no or not much responce from adjusting the low speed needle. Adjust the L.S.needle first, then set idle stop screw to where you want it. Remove all linkages and/or knobs while adjusting the L.S. needle.

 

[Bearcamp]

Re: 1971 Johnson 20 hp smokes at idle.

It also has a very oily exhaust. After running oil will drip out the exhaust tube to the point where you should wipe it off.

 

[Bass2ply]

Re: 1971 Johnson 20 hp smokes at idle.

Bearcamp,<br />I have the same motor and have been going through the same things you are experiencing. I rebuilt the carb and it stopped smoking. After rebuilding the carb, new water pump, head gasket, condensors, points, and coils, I ran it in a can. Had the same thing happen: very oily exhaust and weeping oil. Took it out last weekend and it ran like a champ. I guess that oily stuff is part of the game if we are both experiencing it.