Interchanging triple carbs - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 7 (permalink) Old 08-24-2010, 05:53 AM Thread Starter
Main Motorcycle: Yam XS850
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Interchanging triple carbs

Hi Folks,

I'm hoping to find out all about the carbs the triple triumphs used in the mid 90's, and interchanging issues, and who the carb gurus are on the forum. I will hone my searching skills as time permits, but if there is a a fount of knowledge, let me at it...

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post #2 of 7 (permalink) Old 08-24-2010, 12:45 PM
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Trypcil is probably your man. I think he did dozens of runs on a dyno for a variety of different combinations of carbs in the 90's.

If you are interested in FCR's, then there are several on the site that have them and shared experience in tuning.

Search Mikuni vs Keihin or something similar and a wealth of info will come up.
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post #3 of 7 (permalink) Old 08-24-2010, 03:44 PM
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Hi Russell,

I am along way away from being "an expert", but this link may help you?

Let me know if you think I can help?

(Fyi, I have an XS850G that I am converting to Triumph carbs, but this project is currently on a "back-burner").

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post #4 of 7 (permalink) Old 09-08-2019, 05:24 PM Thread Starter
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Yes, well. It's me again. Same sort of question.. but 9 years later I now have some carbs from something loosely described as carbs from a Triumph Trident/Trophy. Here's a pic, my guess is they are BST34SS carbs.. and I can fit them on my Yam XS850..
All well and good. I think there are two hoses that would go from the top of the carbs to the airbox on a Triumph. What are the hoses for, can they be left open or plugged or do they need to go to the airbox...? Just trying to figure out what to connect, or not to them.

Cheers, Rissole.
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post #5 of 7 (permalink) Old 09-09-2019, 03:57 PM
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Hi Rissole, Those are Mikuni carbs. The Trophy, Sprints and Daytonas used 36mm carbs. Much of the Triumph lineup back then shared many parts. I would guess the Adventurers, and Tridents also used the same 36mm carbs. Somewhere during the 1998 year the Trophys went to Keihin carbs, I don't know if the Adventurer's and Tridents went to the Keihins. Two of my bikes had Mikuni carbs and one bike had Keihin carbs. The Mikuni's have an extra punch when the rev's hit 5 grand, Yeehaa. The Keihin were more civilized with a gradual increase of power as the revs went up. I got rid of the Keihin's and put on Mikuni's. Those hoses you are wondering about are vent hoses. Usually they route toward the front and go down toward the upper engine case. I connected them together and only have one vent hose down toward the engine case. California came up with something stupid and used little electrical valves that only opened the vents when the key was turned on. I tried out some Keihin flat slide carbs on my Sprint. No setup for an airbox so I was concerned about a secure fitting of the carbs. The only thing holding them on was the rubber manifold boots, with no support at the air intake end. The stock air box does a good job of supporting them. Many guys have tried running without the air box and snorkels. Most results were questionable or not so good. They didn't get the increase in power they were hoping for.
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post #6 of 7 (permalink) Old 09-10-2019, 02:44 AM Thread Starter
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Thanks for that info.. 36mm is a bump up from the 34mm Hitachi's the bike was fitted with. It sounds like I can just leave some open hose on the vents. I read somewhere about leaving the ends out of the wind, maybe I can route to the back under the seat.

These don't have twin throttle cables, pull on, pull off type, as far as I can see. But current throttle cable is a bit too short, so will have to fix that.. 🙂 Cheers, R
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post #7 of 7 (permalink) Old 09-16-2019, 12:44 PM
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I have 2 different 900 triples, one with Mikuni's, and one with Keihin. Been through the rejetting and cleaning process on both bikes. Both are excellent carburetors. The Keihin is a bit simpler. The Mikuni has the built in feature to adjust the needle height with several grooves on the needle. (With the Keihin, if you want to make changes you have to use some kind of spacer and hope it is the right thickness). Once you set either kind up, my advice is to leave them alone. The less you tinker, the better they run. A lot of running problems with these engines is inadvertently blamed on the carburetors in my opinion. ...J.D.

Last edited by Wire-Wheels; 09-16-2019 at 07:02 PM.
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