Reply To: Johnson 5.5 won’t idle

[Don]

You mention that the engine runs OK at full throttle but won’t idle.  It is possible that one cylinder is dropping out when the RPM is lowered, so you may want to use one of those neon inline spark testers to be sure you are not losing spark at lower RPM.  Perhaps you just have one bum plug.  Just cuz the plugs are new, doesn’t mean they are good.  Always start with the simplest issues.  Like others have said, have a look at the sediment bowl to ensure the carb hasn’t sucked up water/rust/crud.  Are the packing nuts snugged up to ensure the needles don’t move around on their own.  You might try resetting the initial needle settings and readjusting.   Does the engine sneeze/cough when the throttle is lowered?  If so, perhaps the tank isn’t  holding pressure.  Keep in mind that the tank must hold pressure or else there will be a crankcase leak and the engine won’t idle.

Finally, I would be very careful about using a 24:1 mixture to evaluate the drain system.  This is a good way to damage the rod bearings.  Always start with the simple things, including rechecking compression.