Re: 1968 johnson 20hp
Trouble shooting.......
Check compression which should approach 100 psi. Should also be fairly even on both cylinders. What do you have?
S/plugs removed.... Spark should jump a 1/4" gap on that model with a strong blue lightning like flame... a real SNAP! Does it?
If the above two areas are as they should be, it's possible that the carburetor may simply be out of adjustment (as follows), but if not, then the carburetor may be fouled and require cleaning.
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.
Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.
Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.
When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
