Fouled plugs are an indication of overly rich mixture and/or late timing. Check the timing and point gap first. Then check the valve lash warm. Finally, check the carburator. It sounds like you might have a stuck power valve or too rich a jet for your engine.

A Rochester "B" should have a 53 or 54 main jet for a 235 and a 57-58 main jet for a 261. The power piston should move freely and hold the ball off the seat when the engine is not running, but should get sucked up into the airhorn and let the ball seat with about 7 lbs of vacuum. The correct gaskets are required for the power valve to work. The most overlooked one is the spacer on the manifold, it should have notches to line up with the small hole on the base of the carb. The other overlooked ones are between the throttle body and the bowl, and between the air horn and the bowl. Make sure none of the passages are plugged.

A stuck manifold heat valve causes a lean condition when the engine is warm.

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