ST G-61 with Perry 4500 carb - will not stop!

[mwoodman]

Here's a problem I have, hoping someone may have an explanation, or ideas.

I have a ST G61, which was a real dog with the supplied carb, so I decided to invest in a Perry 4500.

Fitted the Perry, set up all the linkages and ran the engine.....sweet, smooth idle, great transition, excellent top end.

I was a very happy camper, UNTIL

I moved the throttle trim all the way down to shut it off, and it kept on running.

I increased the throw on low end throttle in my radio, and it kept on running.

I adjusted to idle speed screw to make sure the barrel was closing all the way (it was), and it kept on running.

Pinched off the fuel line to stop it.

Removed the carb, cleaned the throat on the engine, checked the O ring, reseated it, restarted it, and once again, it won't shut off!

Spoke to club members, especially our engine guy, he could not explain it, except to say that maybe the barrel fitting in the body was outside tolerance and was leaking air around the barrel.

To test this theory, we covered the carb throat at idle, and the engine died.

Ideas, comments, suggestions welcome

Mark