Fouling plugs - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 27 (permalink) Old 07-26-2019, 06:57 PM Thread Starter
Grand Prix 125
Main Motorcycle: 71 - T120R
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Fouling plugs

71 Bonneville.
It starts instantly with new plugs and runs great. When the plugs foul, it runs poorly and usually will not start. The plug in the picture was new and ran for about 10 min. Bad carbon fouling. Both plugs look the same. I have been thru the carbs many times and have replaced the floats, seats, jets. I have tried moving the clip at all 3 positions on the needleto lean it out and nothing changes. I tuned the carbs by shutting down a cylinder and tuning the opposite side. And it still fouls the plugs.
If the timing or the valves needed adjustments, it would not run as well as it does - correct?
Suggestions would be appreciated.
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post #2 of 27 (permalink) Old 07-26-2019, 08:11 PM
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what plugs are you using?

i be kevin
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post #3 of 27 (permalink) Old 07-26-2019, 08:49 PM Thread Starter
Grand Prix 125
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NGK B8ES 2411

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post #4 of 27 (permalink) Old 07-26-2019, 09:43 PM
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Iím not saying this is you, but : Sometimes when you are trying to figure out something like this it helps to figure out what isnít wrong to narrow down the possibility of what could be wrong. Like stating what has been done to the carbs already. The other thing that really helps is to do a complete tune up and check the compression. What could be wrong ? Anything that youíre not sure is right. If I ask a question on this forum it will help everyone if I do all of the normal adjustments first. It will save days of trading questions and answers back and forth. This is because when someone tells me their bike isnít running right, Iím going to ask when was the last tune up, because that usually gets rid of half the problems.
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post #5 of 27 (permalink) Old 07-26-2019, 11:27 PM
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B8's are a little on the cool side. Try some Champion N3C's. Any evidence of oil fouling?

Htown16, Houston, Texas
1978 T140E Bonneville, 1974 Trident, 1972 Commando, 1971 Commando
1974 Commando, 1970 BSA Thunderbolt, 2004 XL 1200R Sportster
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post #6 of 27 (permalink) Old 07-27-2019, 02:36 AM
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The needle position has little to no effect on the mixture at idle. How are you setting the air screws?

Rod
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post #7 of 27 (permalink) Old 07-27-2019, 05:09 AM
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+1 to redmoggy above.
Had similar in my 77 T140 recently, plugs a sooty black as in the picture. Air screws set a 1.5 turns, so have just taken them out to 2 turns. after a couple of miles plugs were brown. Need the opportunity to put a few more miles at highway speeds to check all is still good.
Good luck.
Andy
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post #8 of 27 (permalink) Old 07-27-2019, 05:23 AM
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Three things to check:
Float levels:
Using aluminium, viton-tipped needles, set the float level to .080" below the cusp by pressing lightly on the TANG only. 'Stay-up' floats are easy to adjust.

Pilot jet
Get a .016" guitar string and insert through the jet (about 1 1/2 inches in) and file the end to remove any burrs. You may need a flashlight to see the jet hole. Spray carb cleaner through the jets afterwards.

Air filters.
Clean them in a bath of paraffin (kerosene), and leave to dry.
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post #9 of 27 (permalink) Old 07-27-2019, 05:35 AM
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I tried every method I read for setting my mixture at idle, I simply never managed to get it right. I eventually gave in and with some scepticism decided to try a Mates Gunson Colortune. Brilliant bit of kit.

Rod
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post #10 of 27 (permalink) Old 07-27-2019, 07:41 AM
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Yes
Had a colourtune for 40 odd years

Anybody tried a twinmax balencer?
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