340 idle problems

It might something simple that's giving you a vacuum leak. I'll usually cup my hand over the top of the carb top to see if it's "looking" to be more rich. I also spray starting fluid in little shots around the manifold while it's running to see if that speeds up the idle.......some might say that isn't safe but in small shots, I don't see any huge danger. I just don't go hog wild spraying it non-stop.

I've had vacuum leaks from using a carb base gasket that didn't exactly fit the top of the manifold.