Re: 1960 johnson 10hp bad miss

[Don]

OK, well that is good info, different carb, same bad idle….So, I guess we can rule out carb issues, and the syncro is OK….
I am assuming you checked compression and that is OK. Any signs of a crankcase leak between the two halves, or perhaps on one of the bypass covers? Again, have a close look at the intake manifold to see if someone has been messing around in there. Perhaps you have a bad reed, or messed up gasket, but I wouldn’t rip into the manifold until the other simpler choices have been looked at.