removed the whole spacer?  should have only trimmed it down to half size.

backfires are normal in a big single. you will never fully get rid of them. i've ridden thumpers my whole life and i like em  they announce your presense.

read post titled white spacer mod in technical section for more information on the subject.

airframer509 wrote on 12/31/69 at 16:00:04:


Part of it might be your shifting technique that causes the backfires on upshift, very rarely on downshift....throttle position and RPMs...

Either way, it is happening when you close the throttle.  You said "pop" which could be different from a backfire.  Depending on the interpretation, I am wondering if you have changed the exhaust.  If so, have you also changed the main jet?

Try easing off the throttle just a touch when you shift. If you let off a good bit, shift, and then whack the throttle, it's gonna backfire. I shift without the clutch for 2-3, 3-4, 4-5, and for 5-4, 4-3, 3-2, 2-N. No backfires, but if I miss the shift point by a couple hundred RPMs, there's gonna be a 98 parted out here... Takes a lot of practice, but, I find it smoother on me and the bike than using the clutch all the time.
-WD