Hellow! I am new here. My brother & I are working on his 1971 Johnson 20 hp. I have the same Identical motor that runs great. His motor has never Idled low without quiting. His motor smokes alot also. We have rebuilt the carb. with kit. Decarbed motor twice. Compresion is 125 on top, 119 on bottom. We placed my carb. off my motor on his and the motor ran pretty much the same, no low Idle and smoked alot. To keep the motor running, the throttle has to be turned up so the roller cam is about halfway from the cams double mark to WOT. We have rest the carb. throat valve by the service manual. Still no low Idle. The motor seem to run good at mid range up to WOT, but will not Idle low. Oil mix is good, 50:1. Fuel Pump is one year old. New plug j4c. With swapping carbs, I would think the problem would be elsewhere. Thanks for your help.
