2003 Bonneville Carb Issues

Still sounds like an air leak but could be a blocked pilot jet. Try spraying some brake cleaner around the carb rubbers while the engine is running and see if the revs change. Easy way to find a leak.

 

Bob Customer
Try a good carb and injection cleaner through the system just to clean out any sludge that is gathering.
Joe.

 

Did you get to the bottom of this? I had a very similar issue with my 2002. It seemed like it was fuel related, mimicking a blocked pilot jet but after two carb strip-downs without success, I realised that it was something else. That "something" turned out to be the coil but it led me a merry dance before I discovered it.

Jim.

 

That is exactly how my bike went too. Don't discount the coil.

Jim.

 

Inlet manifolds or vacuum lines~caps ?

 

Have you checked the diapragms for pinhole

 

I'm having carb troubles too, after the Bonny sat over 2020 as I couldn't get an MOT. In ignorance, I left some French E10 petrol in it. I've cleaned out the jelly gunk from the carbs, used carb cleaner, blew them out with an airline, replaced a broken off No 40 slow running jet ( Not my fault...Really!) It runs on idle with the choke on, but has a massive flat spot if I try to rev it. When I can get above that it revs! Plugs ( New) are grey so it is weak. I will try the airleak diagnostic trick someone mentioned. I've had the carbs off 5 times now. Tried running without the tiny in the fuel line filter
but still the same. Never had this trouble with the old Monoblocs!
Looking at the sparks they aren't the big blue ones i'm used to. They are small and pinkish. Any ideas very gratefully received.