Al, if you had the head off, you should pull the muffler and check the cylinder orientation as someone suggested above. Set the lowspeed needle about 1/16 inch from the end of the spraybar, I have about 12 MDS engines now and they are not a problem. The idlebar plug is good advice, low nitro and lube 20% a necessity Try a heavier prop load, they are easier to set up with a 10x7 or 11x5. When a guy uses a childish anacronym for MDS that tells me he's never owned one. If you lived in the States I'd have you ship your engine to me and I'd spend about three minutes getting it running.