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Triumph TR6 - Misfire prior to power band

I've adjusted the timing to every possible setting and still, I get misfiring at start up and just before I get into the power band around 2400 rpm. She farts and burps from the front three from 2100 to 2300 and I can't seem to solve the problem. Any thoughts? Could it be the centrifugal weights misbehaving? Would the Petronic electronic ignition solve this problem?
Bryn

I doubt only the front 3 would be effected if it were anything in the ignition. How do you know it's the front 3? Sounds like a carb problem, though - give more info, does it happen all the time, only when hot, only when cold? There have been lots of suggestions here:
1) Check the diaphragms for holes.
2) Check that the air valves have about the same opening resistance and fall back down with a good "click".
3) Check synchronization at 2000-2500 rpm
4) Does it stall at idle from flooding? Bad needle valve
5) Manifold, carb connection and hoses for vacuum leaks

Recap all that you've done.
Brent B

Brent;

I thought perhaps it may have been a carb problem as well. The plugs all look good after a good run but after a rough start up, the front three looked black (rich running). The needle valve was indeed off centre (I though caused by the repeated misfires through the carb) and showed signs of wear on one side. I attempted an adjustment and now have both valves rising and falling similarly and dropping with a good click. The misfire problem mainly occurs when cold; cruising speeds are not a problem except for the very occassional hiccup which I can live with. It does not stall at idle from flooding and I'd rather not attempt syncronization myself but I will give it a listen at 2300 rpm.

So, thus far I have;
altered the timing fore and aft
checked the carbs, diaphrams, valve movement,
checked the vacuum advance (suction at distrib end, although movement seems a bit hard).

Today I will;
check hoses,
listen for equal flow through both carbs.

Any thoughts on the electronic ignition option?
Thanks,
Bryn
Bryn

I put a Crane XR700 in mine about 2 years ago and it works very well.

Synchronizing the carbs is really very easy with a Unisyn or other flow meter - you really need to learn that task.

A worn needle is bad news - it (both) need replacement. The needles SHOULD appear off-center when you remove the air valve. They are "biased" by a spring load to lightly drag on the back of the jet, I believe. A much better set-up than trying to align a fixed needle. If one of them is not biased such as the spring being jammed it could cause a problem if it bound in the jet somehow.

Just a guess, but it sounds to me that you're too lean on the back carb, a bit too rich on the front. I base that on the pops & misfires that happen if you try and run cold without enough "choke". Those generally go away after the engine comes up to temp. Good luck.
Brent B

Found the problem(s):
Choke cable had become frayed and was not returning all the way on the front; distributor lock down nut was loose; after I fixed those little nastiest, I accidentally reversed # 3 & 6 spark plug cables. So now it seems fine!
Bryn

Good to hear you got it straightened out, Bryn.

For your info - there are a bunch of bad stories about the Petronix (sp?) ignition in the new July 6-pack archives.

http://www.team.net/archive/6pack
Brent B

This thread was discussed between 30/06/2003 and 02/07/2003

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