Help, my 2003 Triumph Bonneville ran great for 15 years. All of a sudden it stumbles and back fires as I try to accelerate between 2000 and 3000 rpms. Bike idles OK and runs fine at cruise 3500 to 4500 ram. Carb boots looked dry and cracked and showed vacuum leaking. After replacing boots no change in performance. What do I do next??? With engine warm and idling if I pull choke out, add full choke, the engine races to 4000 rpms.
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.
That is how I found the leaking boots, no change in the way the bike runs. Adding some choke helps which again says it must be a vacuum leak. I think I will pull the seat, tank, airbox etc. To get a better look at what is going on. Thanks for the help Bob C
Bob Customer Try a good carb and injection cleaner through the system just to clean out any sludge that is gathering. Joe.
Thanks Joe, That is what I plan on doing, I have some plans for a week or so, but will get to the bike shortly after. Bob C
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.
Thanks for the help, no I am still trying to figure this one out. I do not think it is fuel related as the bike idles fine and runs strong at high RPMS. It must be a vaccum leak somewhere. I look on. Bob C
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.
