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black spark plug

  • Thread starter Thread starter nathan12
  • Start date Start date
N

nathan12

Guest
The second cylinder in from the left on my gs 1100 is fouling spark plugs like crazy. the coil seems to be ok, the plug wire shocked my pretty good when I was messing around with it. if i put a new plug in it is ok for roughly 38 seconds before fouling out again. When taken out the plug smells of gasoline badly. does anyone know a good starting point for figuring this out? thanks.
nathan
 
sounds like your fuel petcock is bad, You7 are drawing fuel throught the vacuum hose from #2 carb.
 
cool

cool

that had crossed my mind, any recommendations as to where to get one?? thanks !!
nathan
 
Since it only takes 38 seconds to totally foul the plug, I'd try an experiment before I replaced the petcock. Rig up a temporary gas tank and plug the vacuum port on the carb. Run it for a minute and see what the plug looks like. If it's fouled, your problem is with the carb. If not, get a new petcock.

If you want to do it even easier, plug the vacuum port on the carb and suck on the end of the vacuum tube coming from the petcock. Slight suction will allow gas to flow into the carbs and you can perform the same test. If the plug still fouls, you don't have a faulty petcock and the fault lies with the carb. If the plug looks good, you need a new petcock. (If that happens, you're going to end up with gas in your mouth....try not to swallow it; if you do, you'll taste it every time you burp for 2 days. (Don't ask me how I know.)

Simple and straight forward and it may save you buying a part you don't need.;)
 
Last edited:
paco13 said:
sounds like your fuel petcock is bad, You7 are drawing fuel throught the vacuum hose from #2 carb.
Click to expand...

Please explain why it sounds like a bad petcock. Is it not allowing enough flow of fuel and starving the cylinder or allowing the flow of too much fuel and flooding the cylinder? Or, is it some other reason.
Thanks!
GS750GUY.
 
ok

ok

yeah the petcock has prime on it. I will try the plugging the vent hose thing as soon as I can, though I suppose its time for a new petcock anyway since its like 26 years old. thanks!
nathan
 
GS750GUY said:
Please explain why it sounds like a bad petcock. Is it not allowing enough flow of fuel and starving the cylinder or allowing the flow of too much fuel and flooding the cylinder? Or, is it some other reason.
Thanks!
GS750GUY.
Click to expand...
There is a vacuum line that goes from the outlet on carb #2 that leads up to the petcock. When the engine is running (and creating vacuum), the vacuum pulls on a diaphragm in the petcock to turn on the fuel flow. That diaphragm will eventually develop a leak, which allows raw fuel to travel down the vacuum line and go straight to the #2 cylinder. Since air has already gone through the carb and gotten the proper amount of fuel mixed in, the extra that comes in via the vacuum line makes the mix for that cylinder only, far too rich.

There are petcock rebuild kits available, but the general concensus on this board is that the kits don't work. You might get a kit for $20-25 and will probably still have a leak due to faulty parts. Better to get a complete petcock for about $60 from your favorite supplier.

.
 
GS750GUY said:
Please explain why it sounds like a bad petcock. Is it not allowing enough flow of fuel and starving the cylinder or allowing the flow of too much fuel and flooding the cylinder? Or, is it some other reason.
Thanks!
GS750GUY.
Click to expand...

some other reason...

it's letting the fuel where it shouldnt - through the vacuum line
this has to to do with the gaskets inside the petcock and a general wear of parts
 
nathan12 said:
yeah the petcock has prime on it. I will try the plugging the vent hose thing as soon as I can, though I suppose its time for a new petcock anyway since its like 26 years old. thanks!
nathan
Click to expand...

Don't make us do the math!! List the year and model of your bike; it will make responses sooooooooo much more appropriate in the future.;)
 
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