Carb settings

Joined
Jan 2, 2009
Messages
280
Can anyone assist me.
I have a Triumph T110 with a splayed head 3134 cams both sides and Amal monoblock 389/689 carbs
What Jet sizes should I be using? Also what groove should the Tapered needle be on?
I have maucked about abit as this bike seems to not pull weel from low revs, probably to do with the cams?
It also 'pinked' really bad until I went up to 260's..now I have 280's, with a missfire...
Thanks,
Stu
 
Joined
Feb 10, 2009
Messages
1,928
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I’ll reply here to your query in the new Norton thread.

I tune the carbs like this. Other prefer to do more plug reading and they’re not wrong- especially for full throttle tests to find best main jet size.

Engine good and warm but not so roasting that smoke comes from the cylinder head!
If the needle clip is in the wrong notch, the mixture will be very rich or very weak. If you’ve got any pinking, try lifting (enriching) the needles. If it’s blubbery and fluffy pulling at low revs, you may be too rich on the needle.

If the main jet is too big and the needle is fairly ok, the engine will hesitate for a moment when you close the throttle very slightly after running on full throttle, that is from fully open to about 7/8 open. If the main jet is too small, it may feel faster at 7/8 throttle than full throttle, but I keep putting in bigger and bigger jets until I know it’s too rich, then lean off until correct. If plugs soot up at full throttle, you’re too rich on the main jet. If it seizes at 90mph into a headwind, you may have been too weak!

Slide cutaway: I just experiment until I find ones that run without richly blubbering or weakly spitting and banging at just off-idle. Fine tuning at a very small throttle opening can be done with the idle mixture screws, although that can spoil your idle.

Throttle stops are about right if it idles at about 1000rpm, firing on both cylinders and if temporarily screwing either throttle stop in 1/8 of a turn makes it speed up.

Sometimes I can do the slow running adjustments by ear but sometimes I seem to lose my touch and use a Colortune, to ascertain that a cylinder is firing regularly and not madly rich.

I wouldn’t say lack of low-end power is a characteristic of E3134 cams, but it depends what you call low revs- mine is certainly happy fro 3000rpm upwards.

1955 T110, still with iron head;
Twin 28mm Concentric Mk1 carbs mounted parallel, single big K&N filter;
1970 TR6 cams, which I believe are E3134 profile;
Late unit 650 “9:1” pistons 60 thou oversize, which appear to give about 8:1 true compression ratio in the old head.
All lashed up in a 1957 Dominator 99 frame, with dual seat and Slimline road tank chopped to fit the Wideline frame.

Can’t post a pic until I get home, away from work’s Big Brother blocking devices, but it’s certainly a bit scruffy.

Running well, although the idle and just off-idle has gone a bit funny again. I don’t have any settings to copy, but when I had a single 1+1/8” Monobloc, I ended up with 340 main jet. I think I have 240 main jets in the 928s
 
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