I have never tuned a MCP for my TT42's. I simply cut the 1.75" off of the Macs header and glue it into the can and they run so good at that length that I have never even had the desire to attempt to fine tune one.

But I have found that WC 15% runs great yet WC 10% runs like crap in these engines. I find it hard to believe that 5% would make that much of a difference but it does...atleast this brand of fuel on a TT42 w/ MCP.