I haven't been following all of the threads, so what I have to offer may
already have been mentioned.
Carbon buildup in the combustion chamber will cause run-on due to the fact
the carbon deposits may absorb fuel and glow. Much like a glow plug in a
diesel engine, causing the engine to "diesel."
Disassembly of the head and mechanical removal of the carbon should solve
Another alternative used back in the 60's, was pouring Bardol down the
carburetor until the engine stalls. Wait 15 minutes or so, restart the engine
burn off the carbon deposits (and kill a few mosquitoes in the process).
For all practical reasons, Bardol was nothing much more than an expensive
cup of Kerosene which will give the same result.
Hope this helps.
60 BN7 (in boxes)