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Join Date: Jul 2006
Location: Kennett Square, PA
You know, this may seem strange, but I bought a project bike a couple of years ago that behaved somewhat similarly to what you've described in previous threads (surge-and-die behavior or just crazy-scary surging) and the problem was that the surge tank itself had a small crack in it. I was unable to find it until I was pulling the engine and doing some other things to the bike, but it turned out to be a hairline crack along a seam.
Failing that, double-check where your rear carb boot goes into the tank - there might be a leak there, or a crack in that boot (or in the tank where the boot gets inserted).