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post #1 of 9 (permalink) Old 07-15-2012, 08:45 PM Thread Starter
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carbon fouled plugs

Suggestions about how to proceed in tracking down the cause for carbon fouling the plugs on my 72 Bonneville? It is a recent problem....plugs foul out after only a few miles of riding. I drained the tank, installed lower octane fuel, but the fouling continues. Any ideas? Mike G
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post #2 of 9 (permalink) Old 07-15-2012, 09:20 PM
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Please add your location. How Octane is rated differs across the world.
<------

In N.America NO lower than 91. 93 is best if it's available in your area.
It's not likely a fuel problem but a Carb problem. The air screws should be your starting point.
You might find this helpful.
http://www.jba.bc.ca/Bushmans%20Carb...g.html#SYNCHRO

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post #3 of 9 (permalink) Old 07-15-2012, 09:53 PM
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Low-octane fuel is not a great idea.It will still run rich,but you could now burn a hole in a piston crown,from detonation.
It could even run slightly richer with low-octane fuel.

The most likely cause of richness is dirty air filters or worn needle-jets.The needles don't wear much,and the parallel part should measure 0.0985" diameter.The jets are usually worn out at 10,000 miles,and a worn jet causes richness.It's not so easy to measure the diameter of a needle-jet.A 106 needle-jet should measure 0.106" in the orifice.If it measures 0.1065",it's worn out.
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post #4 of 9 (permalink) Old 07-16-2012, 07:57 AM
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As mentioned, check your carby settings to eliminate mixture & synchronisation issues. How old are the coils ? How good is the spark?
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post #5 of 9 (permalink) Old 07-16-2012, 09:46 AM Thread Starter
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Thumbs up carbon fouled plugs

The bike is being ridden in the MidAtlantic region and used high octane successfully until til this recent problem. I'll go through the carbs next and look for issues there. Thanks to all who replied.
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post #6 of 9 (permalink) Old 07-17-2012, 01:31 AM
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[QUOTE=shrugger;2301354]Please add your location.

<------




Where You at? Where you from?????????

Check float height and carb settings ------ Its tooooooooooooooooo Rich.................
Make sure you using the correct plug!!!!!!!!!!!!!!!!!
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post #7 of 9 (permalink) Old 07-17-2012, 10:19 AM Thread Starter
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carbon fouled plugs

Went through carbs, cleaned pilot jet, blew out main jet, checked float, checked dual carb cables for synch action. Someone suggested the air slide could be hanging up, but it appears to move freely with the cable. Can anyone please explain its proper operation? Air slide fully up means.....? Slide fully down means? Thanks for all your replies.
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post #8 of 9 (permalink) Old 07-18-2012, 05:20 AM
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Air slide fully down means you're choking it and making it very rich.
Air slide fully up for normal operation on a warm engine.It should be right up inside the throttle slide.
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post #9 of 9 (permalink) Old 07-18-2012, 09:26 AM Thread Starter
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Thumbs up carbon fouled plugs

Thanks.....I really appreciate all your help.
Mike G
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