If you haven't already, I'd suggest putting some red or green Loctite around the base of the 1.45" v main body's boosters where they're supposed to mount flush against the body. The last couple of QFT/Proform main bodies I bought didn't have the boosters swedged tightly enough to keep me from rotating them with my fingers, so I corrected their alignment w/ the venturi bores and added Loctite to seal 'em. Nothing like a hidden air leak to cause a mystery tuning issue...