04 Bonneville - Ran Lovely- Now Misfires Low Revs

Mark Sansom · Jun 9, 2025 at 3:19 PM

Purchased 04 Bonneville via `Motorcycle Supermarket` type place 500 miles ago. 300 miles into it swopped original exhaust for aftermarket exhausts...better mid range power band, no low rev faltering and a marvelous head turning sound.
BUT now misfires on all revs. `Ol Boys` on a run out suggested fuel additive to clear carbs. Lovely for 20 miles and now runs erratically.
Help. Ive tried `marble` in SAIS pipe...worked for bit. Considered removing SAIS components...comments please.

Tim Gibbs · Jun 14, 2025 at 9:19 AM

If you changed the pipes you need to check that the jets are correct. Standard size for oem exhausts are 110, aftermarket pipes may go up to 115 or even 120.
That is a starting point, together with an ultra sonic carb clean.

joe mc donald · Jun 14, 2025 at 9:48 AM

Mark Sansom said: ↑

Purchased 04 Bonneville via `Motorcycle Supermarket` type place 500 miles ago. 300 miles into it swopped original exhaust for aftermarket exhausts...better mid range power band, no low rev faltering and a marvelous head turning sound.
BUT now misfires on all revs. `Ol Boys` on a run out suggested fuel additive to clear carbs. Lovely for 20 miles and now runs erratically.
Help. Ive tried `marble` in SAIS pipe...worked for bit. Considered removing SAIS components...comments please.
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@Mark Sansom @Tim Gibbs has answered you question handsomely