67 Johnson 20hp running rough

[Chuck Zuck]

I have cleaned up the carburetor on it. When I got it running it ran fine for a few minuts and then it started kicking like it is back firing or something. The longer it runs the worse it gets. I checked the plugs and the top one looks good while the bottom one is wet and doesn't look like it is firing as much. Does anyone know if I should be chasing a fuel problem or electrical one? The idle speed needle was in bad shape but seams to have been that way for some time.

Thanks
Chuck

 

[kbait]

Re: 67 Johnson 20hp running rough

Compression test is first, spark test w/a tester is 2nd. Get results and ask again! Sounds like weak spark on one lung to me, but could be failing head gasket...

 

[lindy46]

Re: 67 Johnson 20hp running rough

Could be a bad coil which cuts out when it gets hot. Are the plug wires on the right cylinders? Front-most coil fires the top cylinder. Could also be a sheared flywheel key which messes up the timing.

 

[Chuck Zuck]

Re: 67 Johnson 20hp running rough

Thanks guys! I will get a spark tester and let you know how it goes. The compression was good like 120 less then five pounds difference.