My 1981 KZ1100A is stock except for Dyna 2000 ignition, WG coil mod and mufflers, which are 19" turn outs attached to the stock exhaust pipes. You can see through the mufflers although there are two scoops sticking out into the air path that I guess direct some of the exhaust into a baffle. The scoops in total obstruct about 40-50% of the internal diameter of the pipe. I just got the bike running and it's been backfiring quite a bit, even when going at a steady speed in the higher gears. I had new valves installed last week and I rebuilt the carburetors last summer. The carb holders and exhaust gaskets are new. I checked the carburetor float levels and two are right on and two are high, so I don't think they are causing the backfiring.
From looking at the posts on jetting it seemed like the less restrictive mufflers may be causing it to run lean, resulting in the backfiring. I put the stock mufflers back on today and it ran great - no detectable back firing and noticeably more power, but I like the look and sound of the turn out mufflers. Would larger main jets help? The current ones are 120 and I have a set of 125s that came with the rebuild kits. Just because it's such a pain to change the jets, I'd rather only do it once, so if it's more likely that 122.5 jets would work best I'll order a set of those, but if there's a good chance the 125s are the right size, I'll put those in. Any advice?
1981 KZ1100A1 Shaft
2007 BMW R1200R
