Intermittent Poor Running (Carb - fuel/air issue?) - Triumph Forum: Triumph Rat Motorcycle Forums
Air Cooled Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, Bobber, T100, Speedmaster, America, Thruxton, and Scrambler. Sponsored by:

LinkBack Thread Tools Display Modes
post #1 of 19 (permalink) Old 01-22-2012, 07:14 PM Thread Starter
New Member
Join Date: Apr 2011
Posts: 16
Intermittent Poor Running (Carb - fuel/air issue?)

I will unfortunately have to make this a bit lengthy to pass all pertinent information...

I am now $420 in the hole trying to fix a problem with my 08 America. From time to time, the bike runs like crap, like it is either starved for gas or is way too rich. I have to rev way up to start out to avoid stalling, can't shift beyond 4th gear without stalling even at 55 mph. Smells of gas when running and the MPG goes from approx 45 to 30-35. Further, I am beginning to get discoloration at the pipes due to this.

Have had it since May of 2011, bought used from a Triumph dealer and before taking had the TOR long pipes put on it to replace the stock pipes. I asked the dealer to adjust the carbs for the pipes, they did not tell me what they did to set it up. It ran perfect from May until some time in late November for about a 1000 miles before I first had the issue.

Taken it to two shops already, the first, a Triumph dealer (not the one it was bought from) cleaned the carbs, adjusted fuel/air mix and replaced the fouled plugs ($300). They never gave me a straight answer regarding what caused the problem. Did note that it now has a 42 pilot jet and told me that a 40 is stock. They suggested a jet kit but did not indicate that the lack of a jet kit was the problem with it running poorly.

Following this, it ran fine for about 4 days and began the intermittent issue again. I then tried smaller shop and they tightened the intake clamp and adjusted the fuel/air mixture ($120). The mechanic mentioned that the air injection tubes were capped. Apparently this is a common modification made to help the bike run better? Anyway, he did not suggest changing it.

Well, it ran fine for about 5 days until today and I had the issue again!

No rhyme or reason to when it happens, cold, hot, after it has ran for a bit, right at startup, it will sometimes resume running well after having the problem at startup, etc. No patterns at all. Further, it either runs 100% fine or has the issue, no in between. When I am going down the road while it is running bad and it reverts to running ok, it occurs in a split second and will generally run fine until I shut down. After setting, it may run fine or it may have the issue again at startup.

Wondering if anybody has had a similar issue with a carbureted twin Triumph (02-08)? Any suggestions are welcome. I will contact the second shop tomorrow. The most frustrating thing is that it only occurs intermittent so perhaps the mechanics have not experienced it run like crap. It is miserable to ride and I am causing the pipes to discolor so WANT IT FIXED!
Gooberkat is offline  
Sponsored Links
post #2 of 19 (permalink) Old 01-23-2012, 01:43 AM
Formula Extreme
Main Motorcycle: '03 America
Senior Member
Join Date: Oct 2008
Location: San Francisco
Posts: 705
Other Motorcycle: GS750 rat
Extra Motorcycle: GS750 chop
You can run a search for air injector removal and see it's a very common practice to remove it. It actually eliminates a possible point of failure so thats a good thing if they did it right... you can do a quick visual check: right next to your spark plugs should be some bolts that look like drain pan plugs. The other thing to check is the vacuum line that controls the AI valve. It should be removed and the nipple capped. Here is a picture of that nipple where the vacuum cap has dry rotted:

There are 4 totally nipples like this you should check actually, one on the carb side and one on the head side of the intake for each carb.

Although your situation sounds more sporadic, a common problem you should check to eliminate is the vent tube for the carbs hanging in turbulent air. It hangs from between the carbs and is routed down behind the engine on the left. Check that this and the gas tank vent hoses are not clogged and then trim them higher and at an angle(there was some debate about whether the angle should be forward or backward facing, so long as it's out of the turbulence it's fine either way IMO)

Edit, another thing to check is the seat flexing down too much and squashing the Ignition Control Unit. I'm not sure which bonnies are affected by this as the ICU is mounted to the back bone on the America, but I've seen that problem posted a few times here.

Last edited by Verde; 01-23-2012 at 01:50 AM.
Verde is offline  
post #3 of 19 (permalink) Old 01-23-2012, 04:07 PM
Main Motorcycle: Thruxton
Senior Member
Gary_spain's Avatar
Join Date: Jan 2010
Location: Madrid, Spain - formerly Wigan, UK
Posts: 283
Other Motorcycle: Rieju Tango
Its also a good idea to check the gas tank breather hose and make sure that it's not kinked or blocked as this would gradually form a vacuum inside the tank and eventually starve the carbs of fuel.

Foto is courtesy of Forchetto (its a Bonnie, but the America should be close):

Another test is next time the bike starts running rough take the gas cap off (or loosen) and see if running improves.

I would also request that those "mechanics" refund your dosh. Here in Europe a repair is guaranteed for 3 months by law, but I see you talk of Dollars so you could be in the US. (Fill out your profile please)

07 Thruxton: TEC 2 into 1, K&N, TTP Breathe Bellmouth, 135 mains, 40 pilots, std. needles, 1 shim (0.65mm). All baffles removed. Bitubo Fork Cartridges. Bitubo Rear Shocks. TEC Steering Damper. 3 Pot Nissin (Honda) brake caliper.
Gary_spain is offline  
post #4 of 19 (permalink) Old 01-23-2012, 04:37 PM
Formula Extreme
Main Motorcycle: '03 America
Senior Member
Join Date: Oct 2008
Location: San Francisco
Posts: 705
Other Motorcycle: GS750 rat
Extra Motorcycle: GS750 chop
Oh, d'oh, I somehow spaced it was an America you were talking about when I edited and added the bit about ICU under the seat.

Originally Posted by Gooberkat View Post
Taken it to two shops already, the first, a Triumph dealer (not the one it was bought from) cleaned the carbs, adjusted fuel/air mix and replaced the fouled plugs ($300). They never gave me a straight answer regarding what caused the problem. Did note that it now has a 42 pilot jet and told me that a 40 is stock.
Unless it changed on the later Americas, 42's are stock. 40's were stock in the bonnies. Pilots being slightly rich would not cause your problems either.

Gary covered the gas tank venting check well. Our vent hose is along the right side of the back bone though. Between the carbs clipped to the vertical part of the frame is the tip over valve meant to stop a gas spill in the event of a lay down. This could be the cause if you determine tank venting to be the problem.

Two more things that come to mind:

-Moisture in the gas. This might only rear it's ugly head when you've had to switch to reserve and gas is being drawn from a lower level in the tank, leading to the seemingly sporadic occurrences.

-clogged fuel filter. There is a mini screen in the line, right at the T fitting between the carbs. Clean that and install an inline filter which you can visually inspect instead.

colinm posted this picture in this thread.

My money is on the vent tubes/air turbulence thing at this point though.

Last edited by Verde; 01-23-2012 at 04:53 PM.
Verde is offline  
post #5 of 19 (permalink) Old 01-24-2012, 05:26 AM Thread Starter
New Member
Join Date: Apr 2011
Posts: 16
I checked the vent tubes and they do not extend too low. Furthermore, the bike runs poorly even when not moving and I think the turbulence would only happen while in motion.

I may be able to talk the first shop into providing an upcoming servicing for free, or at least reduced. Yes I am in America, Florida, and there are no laws about giving money back. the only motivator is reputation and whatever measure of customer satisfaction they are interested in providing.

Thank you for the advice. If I get this figured out I will share the source of the issue.
Gooberkat is offline  
post #6 of 19 (permalink) Old 01-24-2012, 06:12 AM
Grand Prix 125
Main Motorcycle: Prefire BonnevilleAmerica
New Member
Moe's Avatar
Join Date: Dec 2001
Location: Merritt Island FL
Posts: 25
Other Motorcycle: Prefire Cardinal Red BA
Extra Motorcycle: 2007 Triumph America
Originally Posted by Verde View Post
I see my picture made it over to this forum. Yep that's my fat paw. and my carbs on the workbench. Funny thing too as I had pulled the carbs to rework the intake manifold seals. The stealership had fubard them up with yamabond instead of using o-rings.

I created a problem that was more than cosmetic though. Using paper towels to wipe out the bowls, I left a little piece of paper in one that would float and get sucked up against the main jet at 4Krpms. (learned all about lint free at that point )

Now Gooberkat, Two_Wheel_n (on that other site) mentioned how a factory ID tag that had the part number of the fuel level sending unit, ended up floating around the tank and would wrap its self around the fuel pick-up screen and choke the fuel off shutting the engine down. Let it sit for awhile it would float away until it ran for awhile and wrap its self around again.

And that was what that piece pf paper towel was doing.

I still think you have an ignition coil going bad. My black '02 tba had the exact symptoms you mentioned on that other site, "When acting up it idles fine, I don't notice the issue until I try to take off and it stalls or I have to rev way up to prevent stalling. "

So similar: A procom CDI will also exhibit the same symptoms! Look up under your tank on the left side for a pig tail coming off your CDI. Chances are your CDI is a GILL not a Procom. The GILL CDIs rarely if ever exhibit the symptoms mentioned above. Instead you'll lose a spark in one cylinder.

Blowing gravel on premium subscriptions, er off rural roads...
Moe is offline  
post #7 of 19 (permalink) Old 01-25-2012, 08:57 AM
Grand Prix 250
Main Motorcycle: 2007 Speedmaster
skinman's Avatar
Join Date: Oct 2009
Location: Idaho Falls, Idaho, USA
Posts: 80
skinman is offline  
post #8 of 19 (permalink) Old 01-25-2012, 11:32 PM
Site Supporter
Main Motorcycle: 2007 Bonnie T100
Lifetime Premium
bonza's Avatar
Join Date: Sep 2007
Location: Melbourne, Australia
Posts: 1,737
Other Motorcycle: Jeep Wrangler
my bonneville was running poorly recently, but at high speed only.

found the carb vent tube was not in its correct location as I unwittingly moved it during cleaning so placed it back where it should be

and also found that one of the HT spark plug leads was very loose on the ignition coil. matter of fact it was just barely sitting on the coil post and must have been like this since I bought the bike 60,000 kilometers ago because I have never disconnected it on the coil end. tightened the HT lead ferrule so it would fit tight on the coil post.

bike runs ok now. dont know which of the two fixed it.

2007 Tuxedo T100.
Dom Tourers, TTP breathe, DNA filter,baffle gone, 40/140/1 shim 3 turns, TTP igniter tune, Hagon Nitros, Thruxton Bars, Halcyon bar end mirrors, Pingel fuel valve, Monza gas cap, Burton seat, Avon Roadriders
bonza is offline  
post #9 of 19 (permalink) Old 05-20-2012, 09:32 PM Thread Starter
New Member
Join Date: Apr 2011
Posts: 16
Still suffering through this but made a discovery - when the bike is running poorly it is due to the right cylinder not firing. I pulled each plug wire to confirm this. What I need to determine is why the right side is failing. I think it is a fuel issue and is fouling. Lately the bike will run poorly on cold startup (not always though) and rectifies after a few miles and does not revert back until shut off and allowed to cool. I wonder if perhaps fuel is flooding the carb while sitting and fouls the plug until the engine warms up enough to clear it and get the plug firing again? I am testing by shutting the fuel off when I let the bike sit for any period of time beyond a few minutes.

Any further ideas??
Gooberkat is offline  
post #10 of 19 (permalink) Old 05-23-2012, 02:03 AM
Formula Extreme
Main Motorcycle: '03 America
Senior Member
Join Date: Oct 2008
Location: San Francisco
Posts: 705
Other Motorcycle: GS750 rat
Extra Motorcycle: GS750 chop
First of all, always turn the fuel off when leaving the bike parked. Second, check that your oil level is where it should be and that it steel feels like oil. I think our carbs are oriented in a way that if there was overflow it will drain towards the air box, but fuel overflow thinning out the oil can cause serious problems so double check that. Third, I don't feel like that would cause a systematic firing problem, granted I'm not the one sitting on it when it acts up though It could very well be electrical, and the fact that it is not firing sometimes and pumping unburned fuel through the system could be giving you that fuel smell leading you to thinking it is a fueling issue. Assuming you've check everything else already suggested,* I feel that fuel/air problems are a less likely culprit.

It's time to develop a set of tests to identify or eliminate the possibility that the problem is electrical. I'd start by swapping ignition components one at a time between the sides. i.e. swap the plugs and change nothing else and see if the same side still acts up. Then swap just the spark plug wires. Next, swap the coils. Label the wires carefully when you do this so you don't mix anything up. They may be long enough to leave the coils mounted in place, but hook the left coil's wires (trigger wire and plug wire) to the right coil and visa versa so that they effectively change places. If at any point your problem switches to the left you know it is electrical and related to that component you just changed. Have some dielectric grease on hand while you are at it to lube the connectors and prevent corrosion in the future.

A sort of recent thread had similar issues, but the non-running side never fired. That turned out to be the ignition control unit tested by swapping out with another bike:

Best of luck.

*fuel filter, vent tubes, vac leaks, drain float bowls to eliminate possibility of water in there, "sea foam" brand gas treatment next fill-up,
Verde is offline  
Sponsored Links

Quick Reply
All posts must adhere to Forum Rules

Register Now

In order to be able to post messages on the Triumph Forum: Triumph Rat Motorcycle Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter your valid email address, that can receive an automated confirmation message. Otherwise, you won't be able to gain full access.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
Intermittent Ignition Issue? Dollarbill Air Cooled Twins Technical Talk 4 05-31-2011 08:54 AM
Thruxton intermittent electics issue decline Club Cafe' 23 03-24-2011 12:12 PM
Poor running at low RPM Ben0611 Speed Triple Forum 4 09-21-2010 01:52 PM
Intermittent starting issue Ant132 T3 Sport / Touring Forum 5 03-29-2010 01:08 AM
Fuel Gauge OK, Low-Fuel light intermittent andy-D Tiger Chat 3 11-16-2006 04:46 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

For the best viewing experience please update your browser to Google Chrome