If you are using a Rochester B or BC, please look carefully at the carburetor. Hundreds of thousands of electrons have been spent discussing it and if you're running rich it is nearly a promise your power piston is stuck in the down position. And that could be for a few different reasons including the worst...your castings are warped and you're losing the vacuum you need to make the oddball Rochester power circuit work. If that is the case, a hotter plug won't help. There's no way the 235 can burn all the gas a poorly operating Rochester B will pour into it. Good luck. If you need more information about repairing the Rochester, about 3 years ago I wrote some instructions showing how you can straighten it using a simple jig made out of a flat piece of 3/8" steel, four screws/nuts and your gas grill.
