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Discussion Starter · #1 ·
Low RPMs, deceleration, light revs off idle. I'm getting this "puff" through the carbs every once and a while (esp when cold). What is this am I hurting my my engine? Does it need tuning? Please Help
 

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Happens to me once in a while too, the pop in the carburetor. One of the gearheads on the forum explained it, I forget the explanation though.
 

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Puff the magic triumph

Mike, please be a lot more specific about what your bike is doing.
What's your startup procedure?
New bike, how many miles.
Do you have a Haynes manual?
Describe what you are doing when the activity begins, what did you do then?
Did you leave the choke on?
Did you read the owners manual yet?
We just need to know more about what is happening and the conditions around it to make any kind of accurate guess as to your problem.
Just note everything you can that might help us understand what the bike is doing when the things happen.
 

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If it's new

Why hassle with it yourself. take it back to the dealer and show them what it's doing. That is whay you paid the bucks for a new bike rather than a used one..
 

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Check the rubber nipples between the carbs and heads- seems like mine did that when one had cracked and come apart
 

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Discussion Starter · #6 ·
476 miles, 2008 Bonneville. I choke it till it revs up, push choke in and she idles greats, and I take off. Sometimes when I stop at a red light I give the throttle a slight rev and I get a pop in the carb - bike continues to run but the pop messes up the idle for a sec. I swear i feel it blow my pant leg. It seems to happen when I'm coming of idle and taking off as well. If I rev it up a bit then let out clutch no problem. So its def low rpms. Another time it happens is when I'm running higher RPMS coming to a stop I pull in clutch Idle drops give a rev and Pop in the carb again. This is never consistant, it happens every once and a while - more so when cold.
 

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Discussion Starter · #7 ·
I have to bring it to the dealer when i reach 800miles for the follow up and synthetic oil, I'd like to wait until then because the poping isn't that bad and not that often, if I'm not hurting anything I'd like to hold off until then, the dealer is a ways away.

So can it wait another 350 miles? Or am i hurting something?
 

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Sounds like it maybe normal. Many of these bikes pop on decel due to AI which is magnified if you have freer flow pipes that let more air in.
If the bike runs well and you are only getting light popping when closing the throttle you likely are fine.
Hope that helps,
George
 

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Discussion Starter · #9 ·
Sounds like it maybe normal. Many of these bikes pop on decel due to AI which is magnified if you have freer flow pipes that let more air in.
If the bike runs well and you are only getting light popping when closing the throttle you likely are fine.
Hope that helps,
George
Makes me feel a hell of a lot better. Thanks! I'll wait until the 800 miles to bring it up.

I am interested in knowing the science behind it... if anybody knows of that thread that explains it... I'd like to read
 

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Like Izzo said! It is definitely the rubber stopper nipple on the carb has fallen off. This is a common problem.
 

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my bike used to do this (at least the way you describe it) and the problem ended up being the bike was too rich in the mid range and low end and would intermittently drop the right cylinder at idle, so i got rid of the shims and tossed in a bigger main jet for the top end, adjusted my mixture screws and no more problem. it was a p.i.t.a. getting my thruxton tuned for altitude in colorado.
 

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Discussion Starter · #12 · (Edited)
Like Izzo said! It is definitely the rubber stopper nipple on the carb has fallen off. This is a common problem.
Where is this located? Nevermind found it... on there good... not it.
 

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Puff of air on the pant leg?
DEFINITELY the rubber vacuum caps.
You miss one and your bike starts running like crap!
 

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That puff of air and backfire screams rubber stopper/vacuum stopper. Remember there are two of them. ;)
 

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Like Izzo said! It is definitely the rubber stopper nipple on the carb has fallen off. This is a common problem.
I wouldn't say definately although some sort of vacume leak is a possibility. When my T100 spat off a vacume cap the bike ran like a hairy goat, backfiring through exhaust, spitting back through the carbs and idling very roughly. The OP's symptoms don't appear to be that bad.

My T100 used to often spit back through the carbs when new, in a very similar manner to the OP's description, but this reduced considerably once the air injection was removed at 800k and now that the bike has 17,000k on it a spit back through the carbs is a very rare thing.
 

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Sounds like a rubber thingy to me. The airbox would probably capture anything like that. Or you could be a paranoid guy like most of us who have a new bike and it's nothing. AND you have a warranty, so take to the Dealer and fixit.:Wave:
 

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Discussion Starter · #17 ·
Sounds like a rubber thingy to me. The airbox would probably capture anything like that. Or you could be a paranoid guy like most of us who have a new bike and it's nothing. AND you have a warranty, so take to the Dealer and fixit.:Wave:
You know what?.... You're 100% right!
 

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I found this on another site.

Affected Models: Bonneville/T100, America, Speedmaster, Thruxton and Scrambler.

Should a bike (see above) demonstrate faulty ignition coil type symptoms (most commonly an engine misfire), please initially check and adjust the ignition pick-up (IPU) air gap (we recommend an air gap of 0.8mm).

Since changing the IPU air gap in production to 0.8mm, we have had no ignition coil warranty claims.

Triumph manual, chapter 16, page 47 has the alignment procedure...

Might be worth a look.
 

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Vacuum caps and other parts

Hey guys,
I'm having a very similar problem as well with the carb backfires. I'm going to go look for the rubber cap. Where can I find parts like this though? I can't seem to find a fiche anymore. There's also a random bolt from the engine block that I'm missing too.
 

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I have to bring it to the dealer when i reach 800miles for the follow up and synthetic oil, I'd like to wait until then because the poping isn't that bad and not that often, if I'm not hurting anything I'd like to hold off until then, the dealer is a ways away.

So can it wait another 350 miles? Or am i hurting something?
FYI. I know there tends to be some variance, but I was under the impression that the first service was supposed to be 500 miles (it is also stated as such in the warranty & service record that came with the bike.) 800 shouldn't be a problem, but it seems a bit on the longish side. My first service is tomorrow, it will be just over 600 miles. I would take it in sooner, rather than later, since there are issues to be addressed. I would also carefully check your vacuum caps and look into removing the AI crap, you might be able to have the dealer do it during your scheduled service, if you don't wish to do it yourself.
 
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