russb,

I've spent my time around Detroits over thirty years ago and we always kept the piece of plywood handy. Don't expect this to work on a runaway 617 engine. Believe me! Been there, done that.

The air cleaner is NOT tight enough. I ripped off the intake hose and covered the hole to the air cleaner. It didn't lower the RPM by more than 30 or 40%. If the air cleaner were off, you could probably cover the top of the intake manifold and it would work.

BELIEVE ME. Some lessons are very hard learned. I am embarrassed to have to tell how I learned this one, but at the price of my own embarrassment I'm trying to save the same experience for whoever else will listen.

When this happened, I posted it and got a very long thread of discussion. Cutting the fuel line won't do it because there's enough fuel in there to run long enough to spoil the engine. Covering the intake while it is at max RPM might work if the air cleaner is not on the engine.

Merry Christmas,