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post #1 of 32 (permalink) Old 04-10-2009, 06:20 PM Thread Starter
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low speed misfire

Hi all,
I have a 2003 T/bird with stock carbs but with triumph O/R silencers and it has done 7700 miles. I have had it for about 12 months and it has been running ok (except for the bad popping back coz of the open pipes) until 4 weeks ago. I fueled up and within 200yds it started misfiring badly at low speeds so I changed the plugs, it seemed to run ok again and I covered about 100 miles with no problems. last week I took the bike out and the misfire had come back. So yesterday it went into my local motorcycle garage and they stripped and cleaned the carbs, refitted them and balanced them.(although the garage said there is no mixture adjustment on them?) I rode it today it is worse now, it just does'nt like running at low speeds i.e pulling away from junctions or powering out of roundabouts or just poodling at 30mph through towns etc. At high speeds it is responsive and smooth, and goes like the clappers. Can anyone give me any advice as to what could be the problem please?
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post #2 of 32 (permalink) Old 04-10-2009, 06:32 PM
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Sounds like copybook coil failure symptoms ?

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post #3 of 32 (permalink) Old 04-10-2009, 10:09 PM
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Originally Posted by IrlMike View Post
Sounds like copybook coil failure symptoms ?
That's a likely culprit.

The best way for a layperson to test them is to find someone with a T3 triple and swap the coils with the known good running bike.

That will not narrow it down to one coil but will either confirm it's a coil or eliminate them as a possibility.


Last edited by denny; 04-11-2009 at 03:52 PM.
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post #4 of 32 (permalink) Old 04-10-2009, 10:41 PM
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I once fueled up our car and within a couple hundred yards it started misfiring.

It turned out to be that the new fuel had water in it.
I had to have to tank pumped out, and presto the cure.

First off, try to change the fuel and buy it from somewhere else.
Just a longshot, but always try the simplest solution first.
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post #5 of 32 (permalink) Old 04-10-2009, 11:50 PM
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I would still suspect the pilot jets. Clean out the tank and fuel lines also.

They can't find the mixture screws because they are under a plug that must be drilled out. What kind of shop is this you took it to?

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post #6 of 32 (permalink) Old 04-11-2009, 04:47 AM
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Water in Float Bowls ?

Sounds like pilot jet problems alright. Water in the bottom of the float bowls would be my guess. This will effectivily prevent a smooth flow of fuel through such narrow tubes. Given that it happend so suddenly after a fuel top up.
Drain each float bowl via the small allen keyed head at the base of each bowl. Try to catch the contents into a container, any water in the bowls will then be evident.
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post #7 of 32 (permalink) Old 04-13-2009, 04:36 PM Thread Starter
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Hi all, thanks for the pointers, just got back from hols so won't look at the T/bird till tomorrow, hope its water in the fuel, PVL coils are about £54 each!
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post #8 of 32 (permalink) Old 04-13-2009, 10:58 PM
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Two points about fuel which probably everyone here already knows:
1- Never fill up at a station where the tanker truck is refilling the ground tanks, as this churns up any sediment and water in the underground tanks, which can then get pumped into your tank.
2- The worst season for moisture in the gas is not when it is cold, although this is the season when symptoms are most common, but when it is fluctuating between hot and cold, especially with lots of moisture in the air. In my neck of the woods, that is Spring and Fall.
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post #9 of 32 (permalink) Old 04-14-2009, 02:44 AM
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Gasoline contains always water, but problems starts when there is so much water that it separates from gasoline. Water is not soluble to gasoline, but to ethanol it is. If your gasoline contains ethanol, then water is no problem for normal amounts, ethanol burns even when 50%/50% mixture water/ethanol.
If you are sure that you have bought pure gasoline, without any ethanol in it, then you can add ethanol to it. I have preferred 5% mixture in winter time when water in gasoline causes carburetors to freeze (form ice)
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post #10 of 32 (permalink) Old 04-14-2009, 04:18 PM
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Hi, I am having the same problem, replaced pick up coil and igniter bypassed all the lockouts (side stand, clutch, alarm, etc) tested coils and still no go.
I noticed when it was stumbling the tacho was dropping and the alarm light was dimly flickering. Spoke to a motor mechanic friend and he suggested one of the coils was arcing internally and spiking the igniter through the live feed, causing all coils to cut out for a split second, after 4000 rpm or so the stumbling would disappear as the resistance in spark plug would drop allowing the spark in the coil to follow its normal rout. We found the faulty coil by running the motor, disconnecting and reconnecting each coil till we had a steady miss on one cylinder and the throttle could be whacked wide open without any hesitation or stumble.
I notice some people say their coils fail at low mileage ( mine 4700) and some folk say they have done thousands with no problems.
Could this be because the low mileage bikes don't like sitting around or do the high mileage bikes not have alarms fitted. Two reasons I wonder about the alarm, mine died and was replaced 2 weeks before the failure of the coil and the alarm light flickering in time with the cutting out of the coils.

Sorry about the rambling first post, great site.
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