That sounds exactly like my experiences. The Scura's previous owner told me that he set them loose and loud, because that's the way he liked it. So, I set out to try every setting I had ever read about. I tried Euro specs, U.S. specs, and Raceco Specs. The Raceco, I believe is the loosest, which is where it was before, and just so happens to be where it is now. Running the closer tolerances definitely keeps the valvetrain quiet, but at the cost of driveability issues. A lot of spitting, sputtering, and the occasionally backfire. It even stalled a couple of times. So I tried looser and looser settings until I ended up where it is now. Runs like a sowing machine, a loud one, luckily the clutch drowns it out.