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Discussion Starter · #1 · (Edited)
I read a few posts here about the Triumph Trophy 1200 stumbling at speed with many ideas offered up.

I wanted to add my issue (and a picture),

I came from a fuel injected Strint ST 955i, before going to the Trophy which was more suited for long touring. This is my first bike with a carb. I got it two days ago and have put around 300 miles on it (a little over a tank and a half of gas) just to see if it was gonna do any back talking while I was close to home (before getting out in the middle of nowhere). With no experience on this bike, I really had no frame of reference for what smooth should be like however, but I felt like it was running really good.

The bike (engine included) was spotless when I got it.

Today doing 70 down the turnpike with 1/4 tank of gas left it stumbled like it was starving, so I switched to the reserve, and it ran rough for ten or twenty seconds before it simply died. I coasted to the shoulder, panicked slightly, then sat for a minute.

It wouldnt start, so I choked it and it started, but giving throttle still offered a gnarly stumble. I switched to prime which helped, and then back to reserve where it died again about five mins later (I coasted into a gas station luckily).

I added three gallons to it bring it to a bit over half a tank and I started it and rode it the two minutes home.

All the reading I have done suggested a pinched vacuum line, and a few other things like coils, plugs, etc.

My Haynes manual will be here in a few days, so I wont open it up until I get it so I can follow the experts, but I looked around and noticed that of the four sections of the carb, three are squeaky clean, while the number two one is nasty oily dirty (numbered left to right).

Below is a picture.

Does this lead anyone to a possible root cause? It seems strange that a spotless bike two days ago, would have one dirty section now, with the other three still being as clean as they started out.

Thanks in advance for any replies.

 

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Before I saw the picture I would of guessed the fuel cap was not venting, but with #2 carb looking like it does...I don't know...sorry.
Welcome aboard by the way.
Mark
 

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Welcome to the world of Trophy's.

The "1/4 tank syndrome" is a well known issue that has many myths and legends associated with it, some valid and some not.

When I got my bike (1200 '96) it was displaying the classic 1/4 tank syndrome that you describe and here is what I found.

Intially I found, like a lot of others, the vacuum line from number 3 carb (numbered left to right while on the bike looking down) to the fuel tap was a bit manky and cracked at the spigot into the carb. After going AAAHHHAA I replaced with good quality vacuum line as well as re-routing the fuel lines carefully and things went a lot better. No stumble on hard acceleration etc, until I started getting the cutting out again at around 1/4 tank while on longer trips on motorways etc.

This time I tackled the venting of the tank. Inside the tank cap there are two little soft brown rubber button valves which are there (I assume) to restrict fuel pouring out in the event of a serious tip over.

I found that these had "stuck" themselves to the metal. After careful cosideration and the observation that I have had a few tip overs in the past on bikes that had no button valves and I'm still here, I removed them and put them in a little zip bag "just in case".

I've never had an issue since with fuel starvation at 1/4 tank and the bike runs strong until the last drop - so they are not going back in.

If you do take the cap apart, be very carefull to cover the opening into the tank and take it slowly and carefully. There are a couple of springs which are intent on very quick exits - never to be seen again - and a tiny little ball bearing (the key flap detent) which is also a slippery little customer intent on a disappearing act.

Have fun. I'm sure it will fix your problem though.

JohnM
 

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Discussion Starter · #4 ·
Thank you for the tip JohnM.

I will investigate this after work as a starting point.

Any idea why just the one dirty barel though? Three clean ones and one dirty must mean something I am thinking.

Thanks again.
 

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I absolutely agree with the gas cap vent solution. Mine had exactly the same issue. Removed the little rubber buttons and all is well. As for the dirty carb barrel, a sticky float or bit of rust or gunk on the float needle would cause that carb to overfill. Gas should run out an overflow hose but....
 

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Another comment on the gas cap tip over valve solution which also was a problem I had. As was suggested to me in this forum once your bike quits just open the gas cap and see how it runs. My bike dsplayed the symptoms you describe and as soon as I opened the gas cap she ran fine again. I have also now left the rubber valves out. A simple test before dismantling your gas cap if that is not the problem. Good luck.
 

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I had a similar problem that turned out to be a bad fuel tap. I could temporarily fix it by blowing out the fuel tap with compressed air. I ended up replacing the entire assembly and had no problems after that.
 

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Discussion Starter · #8 · (Edited)
I tried the vented gas tank this evening in the garage by running it with the tank cap open, but it didnt seem to make an improvement on the bike at idle.

It makes me wonder if I have gotten a bit of a clog in the carburetor.

I will investigate further into the issue when my Haynes manual arrives, however I do appreciate all of the tips so far ad will be looking into each of them as I troubleshoot further.

Thanks again guys.
 

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Hi

Methinks you might have two problems at the same time here.

The one that is the easiest to diagnose from symptoms is the 1/4 tank fuel starvation which is a classic venting issue and wouldn't be obvious until you are running along the highway at sufficient speed to create the vacuum in the tank - thereby restricting the fuel flow.

The other symptom of the rough running tied with your "dirty" carb may be another known Trophy issue which is the carby float bowl "O" rings.

The float assembly is held up into the body of the carb by two small "O" rings. When these get hard and brittle the float assembly drops down into the bowl, thereby stopping the float from shutting off the fuel and effectively flooding the carb.

Don't go to Triumph, they will charge a kings ransom for the whole float assembly to fix the problem. Suzuki used the same carbs in a number of their bikes and so too did Kawasaki I believe (I think the ZZR 1200). Anyway, the equivalent Suzuki part numbers are listed in the files section somewhere and you can get just the "O" rings from Suzuki at a fraction of the price.

This issue would tie in with your overflowing carb and rough idle so would be well worth investigating. Unfortunately you will have to discover another little Trophy delight - getting the carbies out. (Lots of good Ale and Led Zep on hand help to keep your sanity but it's achievable :censored)

Hope this helps

JohnM

PS Found the part numbers :- the small O rings: Suzuki P/N 13374-46710, and the large: Suzuki P/N 13374-35C00.
 

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Discussion Starter · #10 ·
Thanks for the excellent information John, I will add this to the growing list of things to check.

I plan on writing exactly what the root cause and my detailed findings are as soon as I arrive at the answer.

Thanks again guys!
 

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Faulty tank venting, a low volume of onboard fuel and honking down the freeway at near full song can easily create a large vacuum in the fuel tank. When the tank's vacuum strength exceeds the fuel head pressure, the fuel is drawn back into the lines and tank then the engine burps and stumbles as it runs out of fuel.

The dirty carb likely got that way do to fuel exiting past a float bowl seal or a bit of grit holding the float needle off its seat and creating the overflow, or both. In any case, you're going to have to pull the carb for a cleaning and inspection... after yanking lots of other bits.

As stated above, you have two separate problems to address. Good luck. And do post up results.

Monte
 

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Thanks for the tips John!

My 96 900 has been having these symptoms of 1/4 tank starvation and just starvation in general on a very hot summer day while I'm on the interstate. Now I did ask a guy at a Triumph dealer about this issue and he did say something about some o' rings or something like that in the cap. He said to take them out. I was just browsing the threads pertaining to this issue and you refreshed my mind about what to take out. Now I have 134 miles on this tank of gas at the moment, but I am looking forward to seeing if the removal of the buttons you mentioned will cure my problem! I'll keep everyone posted on the results!!! :cool:
 

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It worked!!!! Thanks a million! I was able to do a personal best 255 miles on a tank of gas and it didn't vapor lock on me at all!!! Now I can go up to around 200 miles regularly before I hit reserve. :)
 
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