help with 6 johnson

[cmal]

I have a 1975 6 hp johnson and I can't seem to get it purring the way it should. Today I cleaned the carb, checked compression and spark. I fired it up and it ran kinda rough for about 2 mins and then stahled out just about the same time the thermostat opened up???? So I fired it up again and noticed that it would only run on one cylinder and the other would cut in and out. While it was running I pulled the cap off of the top plug and nothing seemed to change. I then pulled the top plug right out and put it back in the cap and watched it spark away while the bottom cylinder powered the motor at an idle. Any ideas what could be wrong? is there some way water could be getting into the top cyl???? Thanks, Craig

 

[SeaKaye12]

Re: help with 6 johnson

Sparking across the plug like that does not necessarily mean a strong enough spark to fire in the cylinder under compression. Test it with a spark tester and look for at least a 1/4" GAP SPARK.

Not sure about the water issue; a blown cylinder head gasket can do that; not sure what else.

I'd be betting on the spark though.

Chuck