Engine Run On

You need to try to slow down the idle speed. Even a hundred RPM can make a big difference.

What's your initial timing set at? You could bump it up some, which will increase the idle speed. You can then close down the carb throttle plates some. Make sure your secondary throttle plates are open some as well, this will allow the primaries to be closed some.

Do you have an electric fan? I have seen fans feed back enough voltage when they are turned off and are winding down, and the engine will run on till the fan stops spinning.

I had the same problem. I slowed down the idle and went to a cooler spark plug with no success. Switching to 93 octane solved it in my case.

Just my experience.

Ron

Higher octane solved this problem for me. I was also directed to this link recently:

http://mgaguru.com/mgtech/engine/ro101.htm