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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 11-16-2012, 03:15 PM   #1 (permalink)
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Need a bit of carb guidance.

I know this is cliche, but I just need a bit of direction on my setup and issues before I go spending more time and energy tuning my carbs only to get poor results.

What I've done so far:
-NH Togas. No baffles
-Unifilter
-Removed snorkel and enlarged the filter retainer hole
-Removed the restrictor plate in the air box
-AI removed

Tuning:
-130 Main jets
-42 pilot jets turned 1 turn out
-One shim under the needle (stock '01 Bonnie needle)
-I'm right at sea-level.

Results: Bike starts well enough. Very rough idle to begin with with choke on and then smooths out as the engine warms up. Much much popping on decel. With the engine warm, 1/4-1/2 throttle has good response. The problem is 1/2 throttle to full throttle. It feels like I hit a dip in the power and torque curve. It also feel a little like the dip gets better near the top-end of the rev range like 500rpm before redline.

I really can't tell if I'm running rich or lean. I know, I should go have it run on a dyno but I don't have time for that in the next few days and I'm planning on takeing a 400 mile trip next week on Tuesday. I just want a good idea of where to go from here.

I'm inclined to think I'm running rich, but I know that rich and lean symptoms can be very similar. I'm also inclined to pull my needle and either remove the shim (lean it out) or add a shim (richen it up).

What do you people think?
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Old 11-16-2012, 03:43 PM   #2 (permalink)
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I suspect you're too lean with 130 mains, try 135 and add needle shim and another 1/4 turn out on the mixture screws to see if it lessens the popping.
Sometimes it's difficult to get rid of popping altogether with open pipes.
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Old 11-16-2012, 04:01 PM   #3 (permalink)
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If you get up in the revs in say 4th gear at full throttle where she feels boggy and back off a little on the throttle, if it pulls harder (as you back off) your too lean.
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Old 11-16-2012, 04:20 PM   #4 (permalink)
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It does pull harder when I back off. It's almost like a switch comes on at about 1/2 to 3/4 throttle and the torque just falls away. The bike is still making power, but the torque curve just drops.
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Old 11-16-2012, 04:24 PM   #5 (permalink)
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Here's the thing that bothers me about my 1/4 to 1/2 throttle tuning.

When the bike is still cold and I rev-match my downshifts when coming to a light or a stop, the engine won't rev up. It'll bog and make a noise like it's being stifled. Sometimes, even with the choke in and the engine cold this will happen. The 42s might be too rich on the low-end throttle you think?
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Old 11-16-2012, 04:33 PM   #6 (permalink)
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You won't be able to tell a thing with a cold or warm engine. It needs to be hot...like run for at least 15 miles.
Go back to 40 pilots if you wish but that will only increase the popping.
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Old 11-16-2012, 04:45 PM   #7 (permalink)
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FWIW. I had the same exhausts and airbox mods as you and had the same stifling problems with 130 mains, it just choked at 5000 rpm. The low - middle range was ok with stock needles, 2 x .5mm shims and 2 turns. 137.5 Mains took care of the top end, 42 pilots, Thruxton needle, no shims and 1 turn took care of the popping.
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Old 11-16-2012, 05:20 PM   #8 (permalink)
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Gotcha. Well I backed out the mixture screws to 2.5 turns and it helped with the idle running characteristics!

This is great, however, I'm not sure what it is, but I'm hearing an intermittent ticking noise coming from near the cam covers. It's intermittent, in that it ticks rapidly for about 8-10 ticks and then goes away for 3 seconds and then comes back. I have AI removed, so I know it's not the solenoid.

I'm going to go pick up some 135 jets today and change 'em up out tomorrow. Hopefully that'll fill in that upper mid-range.

Thanks for the help. I just wanted to know whether I should be going down to 125s or going up to 135s.

Last edited by luckyduck; 11-16-2012 at 05:38 PM.
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Old 11-16-2012, 05:41 PM   #9 (permalink)
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2.5 turns is a lot from 1, take them 1/4 turn at a time and try it....when HOT only.
You should get the mains right before doing anything else.

The ticking is probably the valve gear, nothing to worry about. Make sure the oil level's ok.

Last edited by denbow; 11-16-2012 at 06:01 PM. Reason: Addition
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Old 11-16-2012, 06:14 PM   #10 (permalink)
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Lucky, Does the clicking noise sound anything like this? Popping noise starts about 37 seconds in on the first video. I cured my issue by replacing the pilot jets. Went from 42 to 45, those were too rich I think and went back to brand new 42s and I'm still not getting any popping noise. It still wants to sporadically hiccup, but I think that's has something more to do with the air mixture screw. I've got replacement springs, washers and rubber "O" rings in their way to me, once I get em, I'll replace them and see if I have any better luck. If not, Santa's going to be bringing me a new set of FCR39's. Oh hell, he may be bringing them anyways.

http://www.triumphrat.net/twins-talk...ml#post2416143
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