It sounds like you've got a vacuum leak that is putting nothing but air into #6. Try using a propane torch with a piece of rubber hose on the end of the pipe instead of the burner head. Turn the valve on a little, and run the end of the hose around the head/intake area where the manifold bolts on. If the engine smooths out or picks up speed, you've found the area of the leak. A cracked manifold runner is a possibility, but it's more likely to be a warped manifold that doesn't bolt up to the head correctly. Once you find the leak, get the manifold machined, or change gaskets, etc. to solve the vacuum leak problem.
Jerry
Last edited by Hotrod Lincoln; 07/26/2009 3:52 AM.
