question about timing and mufflers ??

[rddaves54]

I had to take my truck back to muffler shop today to have it checked out and the gaskets were burned out where they connect to exhaust manifolds. He told me the timing was off and running hot. He said that because of that the gaskets burned away and the galvanized pipe had the galvanize burn off as well up near the manifolds. It has been two months the pipes have been on.

Has anyone ever heard of that?

I set timing today at 8% and the RPMs at 600. It seems to be running better. When I took air breather off the top of carburetor it was black would timing cause this or do I need to adjust the carbs?