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Discussion Starter · #1 ·
Hi, I have an 04 Bonneville that will sputter and back fire at start and until warmed up. My first guess was bad gas and tried some different gas treatments. Next I tried new spark plugs. Yesterday I got my bike back from the shop with a carb clean. This morning again started with sputtering and a couple of back fires. Had to ride with choke out for a few minutes or else when I slow for a stop and then give some throttle it will sputter and sometimes backfire. Once warm the bike rides great...usually within 5 to 10 minutes depending on how cold it is outside. What should I check/do next? Thanks for any advice.
 

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Check your vacuum caps. There should be 4 of them. See if they are loose or cracked. If any are then can be found at a auto parts store, not the same quality as the Triumph ones but they do the job.

Also check your mounting rubbers for the carbs same deal as above, except you'll have to buy new Triumph ones.
 

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Once you are certain there are no vacuum leaks, remove the pilot and main jets and spray carb cleaner through them and every passage in the carb. I know you have had the carbs cleaned but the only way to know is to see for yourself. If new specks of trash are in the bowls check the inline filter.
 

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Discussion Starter · #4 ·
Thank you. Found vacuum caps at the Yamaha dealer. One of mine was really brittle but still didn't do the trick. Guess I will hit up Triumph for the mounting rubbers next. Thanks again.
 

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How long have you had the bike? Dd this problem just start? Winter storage? Any mods? Jets?

If this just developed after taking it out of winter storage, likely gummed up jets. (Yeah, I know you said a shop cleaned them.) Run some carb cleaner though it.

If it just started this, cracked or leaking rubber parts is a possibility, as note above.

Need more info to help you.
 

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Spark or fuel?

. This morning again started with sputtering and a couple of back fires. Had to ride with choke out for a few minutes or else when I slow for a stop and then give some throttle it will sputter and sometimes backfire. Once warm the bike rides great...usually within 5 to 10 minutes depending on how cold it is outside. What should I check/do next?
Mr. frucker,

Before you spring for new parts that you might not need, test the system for leaks by using some WD 40 or some other spray to diagnose any possible air leaks. It probably isn't the carburetor to intake rubbers that are giving you the symptoms.

When you say "backfires", do you mean a bang out of the exhaust or spitting back thru the carbs? Sometimes that term is misused.
This sounds exactly like a coil starting to go bad, if it's the original Gill coil. The absolute best way to test for this is to swap your coil with a friends if possible, or of course, get a new one. Perfect Ohm readings don't seem to always be correct.

If you can't come by a coil, as you start your bike and it tries to live, reach down and tap the header pipe to feel if both sides get warm at the same time. If one is cooler to the touch that could indicate a intermittent spark on the cooler side.

Charles
 

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Discussion Starter · #7 ·
Mr. frucker,

Before you spring for new parts that you might not need, test the system for leaks by using some WD 40 or some other spray to diagnose any possible air leaks. It probably isn't the carburetor to intake rubbers that are giving you the symptoms.

When you say "backfires", do you mean a bang out of the exhaust or spitting back thru the carbs? Sometimes that term is misused.
This sounds exactly like a coil starting to go bad, if it's the original Gill coil. The absolute best way to test for this is to swap your coil with a friends if possible, or of course, get a new one. Perfect Ohm readings don't seem to always be correct.

If you can't come by a coil, as you start your bike and it tries to live, reach down and tap the header pipe to feel if both sides get warm at the same time. If one is cooler to the touch that could indicate a intermittent spark on the cooler side.

Charles
Thanks. As far as the backfire goes, the colder it is the more popping I get. Sometimes pretty loud other times it's bit more of a sputter with pops. I am the original owner. Bike gas 37,000 miles on it. Pipes and carbs jetted in 04. Winterization consists of stabil and battery tender as I never let my bikes sit unridden for long. I have never changed the ignition coils.
 

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OK, so it sounds like winter storage was not your issue. Bad rubber parts is possible. Spraying with wd40 will help Dx this. If the engine suddenly smooths out (or speeds up a bit) when you spray, that pinpoints where the air leak is.

Next to thing to check is the coil. There are a bunch of threads here about using an ohm meter to test coil. IF you know someone you can swap coils with, that is the best test.

You might also check connections under the seat for tightness. SOme silicone grease on them to kepp water out will not hurt anything.

Good luck and let us know how you make out.
 

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I have run into similar conditions a couple of times. For me it was only on start up and warm up. Once fully warmed the bikes seemed to run normally.

Cleaning the enrichening circuit was what it took to fix it. The stuff that was clogging the jet was a crusty kind of hard substance that would not have been dissolved by something like carb cleaner or lacquer thinner. Just as the crust that stops up your shower head, it would take something to dissolve the crystal like formations that I found.

Since you can't use lime away or LCR in there, mechanical cleaning was the only way I found to remove it. It can be done by only removing the float bowl but I removed the carbs, mostly because I did not understand what I was dealing with and needed to be able to look and poke around.

Picture here

http://artshobbyprojects.com/workbench.html

Art.
 

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Check your vacuum caps. There should be 4 of them. See if they are loose or cracked. If any are then can be found at a auto parts store, not the same quality as the Triumph ones but they do the job.

Also check your mounting rubbers for the carbs same deal as above, except you'll have to buy new Triumph ones.
My 01 has been doing the same thing... I just checked my caps and all of em were dry rotted and cracked up. Replaced em, and purrs like a kitten now.
 
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