Mag side plug fouling

[stinger4me]

Just want to pick some brains. I bought a 75 whip, runs good for about 20 min's then fouls the mag side. After it is fouled it will run fine at cruising speeds but if I slow down and try to go again it will run on one cylinder for a bit and then take off again, running on both. If I take the PTO plug and put it in the Mag side and visa versa, it will run fine for another 20 min and do the same thing. The PTO plug has great color and a good burn to it. Runs great at all speeds when it doesn't foul the plug. The fouled plug is never really dark or black, just more wet than the other one.

Its been a while since I worked on a Rockwell, I've been in the single cylinder world for a long time. Man the whistling sound and the smell of exhaust from that whip brings me back to my childhood though!

Any suggestions would be greatly appreciated, Thanks!

[stinger440]

Switch the external coils and see if that moves the issue to the PTO side. Sounds like the coil gets hot and you get weak spark. Also clean up all the ground connections. And look at the pulse line from the carb, does it go to the mag side of the case? you could have a leaking carb and be loading up the mag side with excess fuel.