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Twins Technical Talk Technical Talk for Hinckley Triumph Twins: Bonneville, T100, Speedmaster, America, Thruxton, and Scrambler.

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Old 11-23-2012, 05:32 PM   #1 (permalink)
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One shim or two?

What theoretically, would be achieved by adding another shim?

This is my setup:

2006 T100

140/42 jets
NBZT needles
1 x 0.5mm shim
Idle mixture screws 3 turns out

It runs pretty good


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Old 11-23-2012, 05:45 PM   #2 (permalink)
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A slightly richer bottom end/mid range.
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Old 11-23-2012, 06:19 PM   #3 (permalink)
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I don't speak out of posing to be a mechanic, only because I have the same bike.

Even with wide open pipes and Thrux needles (sorry I don't know the code, I think that's the needles you have) you should not need a shim, ever, and 3 turns is waaaaay too rich.

With 42's mine ran great at 1 1/4 to 1 1/2 turns, no shims, and that was on a dyno, not guessing with me arse. At 2 1/4 turns, I smell raw fuel.

Just my personal experience.
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Last edited by Bron-Yr-Aur; 11-23-2012 at 06:22 PM.
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Old 11-23-2012, 07:03 PM   #4 (permalink)
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+1. Mine stinks of raw fuel on tickover with the mixture screws anything over one turn with 42 pilots ...thrux needle (NBZT), no shims.
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Old 11-23-2012, 08:38 PM   #5 (permalink)
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Quote:
Originally Posted by kreemsicleT100 View Post
With 42's mine ran great at 1 1/4 to 1 1/2 turns, no shims, and that was on a dyno, not guessing with me arse. At 2 1/4 turns, I smell raw fuel.

Just my personal experience.
Thanks for replying.

The three turns-out wasn't arbitrary - it was the point reached that stopped the bike backfiring and made it run better than ever.

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Old 11-23-2012, 08:41 PM   #6 (permalink)
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Quote:
Originally Posted by PieMan View Post
A slightly richer bottom end/mid range.
... by mid-range, I take this to mean better acceleration in higher gear at higher speeds, right?? - this is precisely what I'm looking for

I'm not exactly sure what you mean by "bottom end" though ....

thanks,

GJ

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Old 11-23-2012, 09:48 PM   #7 (permalink)
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Quote:
Originally Posted by gjones View Post
... by mid-range, I take this to mean better acceleration in higher gear at higher speeds, right?? - this is precisely what I'm looking for

I'm not exactly sure what you mean by "bottom end" though ....


.

Mike was referring to throttle position, not vehicle speed or gearing. Presuming you have the correct size mains, with NBZT needles, as a general rule, shims should not be necessary.
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Old 11-24-2012, 12:28 AM   #8 (permalink)
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Bottom end is your lower rpm range, the twisting force (torque) off idle. B02 made a good point: you have to make sure you're running the right mains. What pipes are you using?
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Old 11-24-2012, 09:51 AM   #9 (permalink)
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Originally Posted by B02S4 View Post
Presuming you have the correct size mains, with NBZT needles, as a general rule, shims should not be necessary.

I take your point. So essentially there is an equivalency of sorts in raising the needle to allow more fuel, and increasing the jet size, correct?

Could you suggest any metrics that could describe this i.e: jet size increments and 0.5mm shim equivalencies ?

thanks,

GJ
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Old 11-24-2012, 09:56 AM   #10 (permalink)
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Quote:
Originally Posted by kreemsicleT100 View Post
What pipes are you using?
Both the air intake and exhaust are low restriction.

thanks,

GJ
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