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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 11-11-2012, 12:55 PM   #1 (permalink)
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Tunning CRS carbs with Innovate MTX-L

ok let it start ....wanted to start new thread about it as need some help and opinion from people with more knowledge about tunning than me

My bike Triumph Bonneville America
- 904 Wiseco kit
- 813 TPUSA cams
- ignitor remapped by Pieman (best money ever spent)
- gutted airbox(no snorkels ,restrictor plate removed)
- "breath" air intake
- Keihin CR-S carbs
- Epco exhaust

Bike going strong no problem there but recently been on dyno and not really happy with result was too rich in a first place ....

after reading a lot on this forum about tunning and how helpful Air/Fuel ratio gauges are ,decided to buy one ..Innovate MTX-L and welded bung into crossover pipe.

Today was my first day riding with gauge on the bike and here we got results; 118 main jet ,needle 3rd clip position

Idle............ 13..........1100 rev
1/4..............11.8.......3200 rev
1/2..............12..........5000 rev

had no chance to open throttle to WOT not enough road and with half throttle was doing 90 mph (shown on speedo)and going up to ton

because i done those markings using masking tape in throttle and housing first time ever noticed that I'm normally using trottle opening from 1/4 to 1/2

Any advice?
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Old 11-11-2012, 06:26 PM   #2 (permalink)
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You need to get the main jet squared out before you start playing with the needle position. Take the bike out where you can pull full throttle for a good 20 seconds & see where you are at on the main jet. The partial throttle conditions are good and rich right now, so no worries about hurting anything. With a 118 main, my guess is you are quite lean on the main jet...

BTW, make sure you order some needle shims if you end up getting bigger mains - or get the appropriate size SS washers from the hardware store (they work) since you're going to need to fine tune the needle at some point.

Regards,

--Rich
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Old 11-11-2012, 08:12 PM   #3 (permalink)
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^ What he said...
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Old 11-25-2012, 02:24 PM   #4 (permalink)
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-ok 120 main(AB jet) read somewhere that it should be the same as Keihin
-needle 2nd clip from top

Idle around 14
from 0 to half throttle about 13,6
WOT down to about 12 (but this is not confirmed as run was to short)

weather wasn't great..very strong wind and wet surface
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Old 11-25-2012, 03:33 PM   #5 (permalink)
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You need to know what the a/f is at redline before you will know what main jet you need.
you dont have to use 5th gear to do this 3rd or 4th will give you a good idea.dont even worry with the needle untill you get a/f wot at redline.Changes to the main jet will change what the needle does.
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Old 11-25-2012, 04:19 PM   #6 (permalink)
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ok where should I be with WOT ?
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Old 11-25-2012, 04:40 PM   #7 (permalink)
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What Mike said. My bike likes high 12s at full throttle for max. power. I'm cheating currently with about 13.5 a/f on a full throttle pull to keep my 3/4 throttle from going pig rich.

The needle selection for the CR carbs is limited and in order to get the correct initial diameter for my setup, I had to go one size bigger in initial diameter (i.e. leaner on the keihin chart) than typically supplied with these carbs. In doing so, the needle length (L1) is shorter/taper happens quicker, thus making 1/2 to 3/4 throttle go quite rich. What is needed for my setup is a leaner needle with a longer L1...unfortunately, there in no such animal short of having one made one-off...

Your current setup sounds promising. But do dial in that main before going further.

Regards,

--Rich
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Old 11-25-2012, 09:13 PM   #8 (permalink)
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they seam to run there best at 12.5 to 13.0 wot at red line.If you are running stright gas closer to the 13.0 if you are running 10%eth closer to the 12.5
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Old 11-26-2012, 03:38 PM   #9 (permalink)
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gas..........the grade is different here than USA or Canada we got 95 in usa its 91
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Last edited by grzegorz; 11-26-2012 at 03:45 PM.
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Old 11-26-2012, 03:51 PM   #10 (permalink)
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A 13:0 to 1 A/F ratio is probably optimal based on what you're saying. What mike was trying to say is that if your gas has ethanol in it, run it a bit richer than that...like mid to high 12s...

Good luck,

--Rich
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