Bonneville America Forums Forums Technical Forums General Tech Backfiring n cutting out 07 Speedmaster

Hey i need bit help with my 07 carb speedmaster,now dome 54k, i had since new with after market pod filter kit and pipes about 30km ago an retuned perfect with correct main jets , BUT now over last week it runs like a pig backfires like hell when its warmed up and when slowing down n sounds like a atom bomb going off then wants to cut out but pull the choke out runs good but with high RPM which aint good cuz have to ride the clutch so she dose not stall and trying to slow down with out stalling is a pain BUT at constant speed over 60k/h she runs perfect, i have had the carby strippped down and was clean as and had compression test and came up strong.
Both leeds were tested with a strobe lite and was constant but only at stand still with high revs.
I love my beast and if any one can help out with this drama of backfiring it would be apprecaited heaps.
Mark

Sounds like an air leak, check over your rubbers on the intakes first, if they are good, take an unlit propane torch and play the unignited fuel over the intake surfaces while the bike is idling, adding the fuel gas to a leak will noticeably change the RPM. Good move on the compr. test, rules out a burnt valve. Could also be a exhaust side leak, but I'm betting on the intake side. This problem has occurred to many on this site, the search function will provide you with a wealth of things to check as well.

Check squirrel condoms first then any other source of intake leaks such as the rubber manifolds.

Be very careful if you use the propane method you don't create a pocket that could ignite. You can do the same thing with carb cleaner.