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Discussion Starter #1
Hi All,

I am in the process of getting a 1993 triumph trident (serial 001053) back on the road after 8 years of standing forgotten. Among other things, the Mikuni BST36 carb is completely gummed up and the needle shows significant wear. most of the internals will be changed.
but I have a doubt regarding the emulsion tube. I find two different emulsion tube sizes mentioned, O-6 and O-8. The bike is completely stock from air intake to exhaust. Can anyone confirm which emulsion tube was used on these serial numbers? I doubt the difference is generally noticeable but....

part numbers
784-232103-O-8
784-232103-O-6
needle J8-5E56

Thanks in advance,

Leon
 

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Hi Leon, I'm in the USA and using 2wheelpros.com website. Triumph didn't bring their bikes to the US until 1995 so their listing stops in 1995 and your 1993 might be different but I doubt it.
The 0-6 emulsion tube goes into carb #2
The 0-8 emulsion tubes go into carbs #1 and #3
Hope this helps,
Greg
 

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Discussion Starter #3
Hi greg,

Awesome. I can not read the writing on the tubes but with your info I should be able to make sense of it. A lot of contradictoire info on the net.

Thanks


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Discussion Starter #4
Incidentally, does anyone have info on the reason why the middle cylinder is set leaner than the outer two?


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Center cylinder is set a bit leaner because the air flow through the stock air filter to the center cylinder is more restricted than the two outside cylinders
 

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Discussion Starter #7
Hi All,

Dave, thanks for the clarification on he lean cyl 2 situation (it did take me a while to get my head around it.)

Would it be fair to say that the general consensus for the "best" carb set up on a stock bike (I am including M. fitzwater's advice) is as follows:
cylinder 1 and 3:
needle: 5E56
emulsion tube 784-232103-O8
main jet 130
idle jet 40

Cylinder 2:
Needle: 5E56
Emulsion tube -O6
Main jet 125 or (127,5??)
idle jet 40

2-2,5 turns on the air mix to get the CO level to around 3%

I am writing this now from memory and I know this is not the stock set up but supposedly this is the set up which flattens out the midband power curve a bit and makes the going just a tad better.

Do i have this correct?
 

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Hi Vaporlock, Emulsion tube is made of brass, the needle is made of stainless steel. Guess who wins that battle? It take about 60,000 miles and then the emulsion tube starts to oval from the constant rattling of the needle inside the tube. I've got the main jets on my Trophy all the same. 127 were a bit rich and 125's in all three carb gave a nice toasty look to the spark plugs. Same settings on the needle clips, the middle notch. Now this is with stock Trophy mufflers. Other mufflers will require something different. As for #2 cylinder carb being leaner I wonder what's up with that. Are they leaned out on # 2 to comply with gas emission numbers? Watch for the color on the spark plugs.
 

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If you put a vacuum gauge on these engines at an idle, you can see why you get a lot of wear. The needles are constantly on the move at idle due to vacuum pulsations cause by cam overlap. The problem is probably more pronounced on the engines with hotter cams. My solution is to install a balance tube between the carburetor vacuum ports. The idea is to negate some of the pulsing. I have two of these engine. Both set up like that. One I have run that way for almost 17 years. ...J.D.
 

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Discussion Starter #11
Hi Greg hi Wire-wheels,

Yes, with that kind of needle wear the emulsion tubes must be nicely oval and a few sizes up. the lean situation has something to do with the cylinders position in between number 1 and 3 with an airbox which has the airflow wel directed toward the two outer cylinders . I assume the middle cylinder has therefore a bit less access to all the freshness and in consequence needs a leaner setting. So far what I have understood of the info found and heard. not much is available on the subject.

Wire-wheels that is interesting. I had a similar thought: what would happen if instead of capping the vacuum spigots you would connect them together. do you see the difference in pulses when hooking up the vacuum gauge?
 

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You will have to judge for yourself whether linking the carb ports is beneficial or not. My results are inconclusive. In my mind it stands to reason it would smooth out the vacuum signal. But I have never put a gauge on it to see. It is just something I do. ...J.D.
 

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Discussion Starter #14
Hi Vapor Lock, Mine are capped together.


"Capped together" as in linked. Or individually capped?

I find the idea of "balancing" the vacuum side of the three carbs interesting. "Belly feeling" would suggest only benefits or could it generate a loss somewhere.

I never had more than two cylinders on a bike. going from one to two and now to three, every step brought new and interesting mechanics with it.

Interesting stuff.



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I’m currently rebuilding a ‘95 Sprint and going through the same carb de-gunging process. I reckon that if I can’t get the BST36 carbs to run right it might be cheaper overall to get some RS36s to replace them....
 

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I connected the #1 & #2 vacuum ports and they connect to the petcock. The #3 port goes to the vacuum driven Scottoiler. Connecting the vacuum ports was a suggestion from a senior Triumph mechanic, I noticed that it smoothed out the idle. Another thing that I noticed was the sound at idle, what rattle trap. A guy asked me if the engine was a diesel. Adding a Dynojet carb kit helped get rid of some of the rattle. I guess when Triumph built the 900 engine, how it sounded was not a concern.

As for rebuilding the carbs the only re-occurring problem has been the idle fuel jet. The lengthwise hole is only 0.014 inch in diameter, that's about the size of a wire brush bristle. So if I let my bike sit for a few weeks sometimes one of the jets gets clogged. Make sure you have a screwdriver that fit perfectly into that idle jet. I bought a jet and then went and bought a screwdriver that fit the jet. Also check the vacuum cap rubber for holes or a tear.
 

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Discussion Starter #17 (Edited)
I’m currently rebuilding a ‘95 Sprint and going through the same carb de-gunging process. I reckon that if I can’t get the BST36 carbs to run right it might be cheaper overall to get some RS36s to replace them....
mikuni RS36 sound promising, would love to try them. finding some second hand will probably need a rebuild as well.

anybody around who did this swap? considering the cost of a complete rebuild, 950 euro is not that bad.
 

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Discussion Starter #18
Yay, the carb rebuild is a succes.

After 8 years of standing still with half a tank of petrol there were not many open pasages left. After taking the plastic bit of and a good long soak in carb cleaner, a warm ultrasonic bath and a bit of scraping and blowing , put it all back together. Looked like new.

The tank needed more work actually the out of rust and crud was impressive. Cleaned it out, rebuild the petcock, took the tanklid apart , clean some more.

Put everything on the bike primed some time and nothing. Just as I was about to give up trying thinking no gas or no spark, tried one last time and of she went. But only on the choke. Giving gas would stall her.

Took the carb of again, turn the idle air mix screws from 2,5 to 1,5 and the did the trick. Now for the fine tuning.

I am a happy camper today.


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Discussion Starter #19
Right, I do not manage to reach the airmix screws with the cheap options. I will need to invest, taking the carbs of to adjust them gets old quick.

I am back at 2 1/4 turn. At 1.5 it would stall when trying to gas. Letting go of the gas would keep it running . It could be carefully nudged over 3000/4000 rpm . Once over it would react well all the way up. So I think idle mix too lean. Take the Carb of 1/4 turn more , put it back together, try , no joy, take it apart again 1/4 turn etc until it starts good. When warm it almost reacts the way it should. But still not quite. Opening the gas too quick of idle and it sort of dies. The search continues.


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Hi Vaporlock, It's good after 3000/4000 rpm. That's a clear indication that you have either dirty or clogged idle fuel jets. Opening up the air screw won't unclogged the jet. Get the right size of screwdriver before trying to taking out the jet, it will be tight. 1&1/2 -2 turns out should be enough.
 
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