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One cylinder fouling up

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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My #2 spark plug keeps fouling up. It started doing this intermittently a few weeks ago, and the frequency has increased to where I now can't take the bike more than a mile from home.

When I look down the plug hole there is a lot of carbon build-up so the bike is running too rich. Its fuel consumption has also made me think it is too rich. All the plugs are sooty, another indication of running rich.

However, there is also a problem with the spark-plug. When I pull the plug cap from #2 there is no change in the idle speed (pulling other plugs stalls the motor). If I hold the plug cap an inch or two away from the fitting then the plug tries to fire.

I get good spark from that lead. Put a screwdriver into the plug cap and it will spark about an inch to the motor.

The plug caps checks out a 5k ohm. I have reseated the plug lead into the coil and the cap. The paired #3 plug has no problems.

Any ideas about what holding the plug lead away from the plug indicates?

Any ideas of how I can get this cylinder firing so I can burn out the crap.

I'm already working on a new carb set so I can get the rich burn back to normal.

Thanks
Kim

PS Anyone know a good fuel additive for decoking a motor?
 
You might try swapping the #2 & #3 plug wires. If the misfire stays in the #2 cylinder, then it's probably just a bad plug. If #3 starts mifiring, then it's a bad wire or coil.
Sounds like leaner jetting is necessary either way.
Berrymans B-12 will help some with removing the carbon.
Mike
 
You say that when you pull the plug that the idle doesn't change. Well, that means that that cyluinder is misfiring but that would cause wet fouled plugs. If your plugs are sooty, then the cylinder is too rich. Are you sure that the plugs are not wet?
 
Since the vacuum for the petcock comes from the #2 carb (1980 newer w BS carbs). I would sugest that you disconnect and plug the vacuum line and operate the petcock on prime and ride it to see what happends. If plug doesn't foul. That tells you the petcock needs repair.As to it running rich? without knowing any history it would be hard to tell. May just need adjustment? Try to turn the air screw out 1/2 -1 turn. (on the intake side of the carb)
 
About the running rich, how old is your airfilter? If it's very dirty it will let less air through and richen your mixture resulting in the sooty plugs you discribed.
 
If one cylinder is being lazy (ie fouling) there may be a false reading on the other plugs. getting the foulin solved forst will allow a better look at any other problem.
 
I think Slopoke and Alwyn hit it with the petcock diaphram solution.

Broken diaphram -> #2 sucking fuel directly through vacuum hose -> #2 flooding

Pull off the vacuum hose from #2 to petcock. If it locks like gas has been going through it, there's your cause.
 
AHA, broken diaphragm flooding carb. My GFs bike has a similar problem. Guess I know where to start looking now. Never thought of that.
 
Elementry my dear Watson.
Well actually i read it on the old Q and A sometime aqo. Better yet ill bet one of the fellows put Al and I wise to it when we complained about the sudden and unexplainable poor running especially when we slowed down or was driving in traffic. :D
 
VStan said:
AHA, broken diaphragm flooding carb. My GFs bike has a similar problem. Guess I know where to start looking now. Never thought of that.
Click to expand...

ha yeah me too i even paid like 90 bucks at a shop just in labor and they told me my carb are dirty after i just rebuilt them and soaked the in carb clean dam its always where you dont look
 
micksdrunk said:
VStan said:
AHA, broken diaphragm flooding carb. My GFs bike has a similar problem. Guess I know where to start looking now. Never thought of that.
Click to expand...

Ha-- yeah me too i even paid like 90 bucks at a shop just in labor and they told me my carb are dirty after i just rebuilt them and soaked the in carb clean dam its always where you dont look
Click to expand...
That one is a standard fooler on most gs models. I imagined everything but the petcock when the bike started acting up. I used to marvel at how the floats didnt leak when i shut the bike down and didn't have to turn off the fuel. Old school thinking never heard of a vacume operated diaphram. My 600 elimiator was the same and i always bragged about the precision of the carbs because they never leaked either. WOW 8O 8O
 
Thanks for your replies, folks.

I tested the petcock, it's working fine.

The carbies have been worked over since my post and the float levels adjusted to run a little leaner. Also dropped the needle (raised the clip) one notch for a leaner mid-range.

I also tested the coils and plug leads, all OK. Swapping 2 and 3 did not make any difference. I made sure that the connection points of the leads into the coils were cleaned up with no oxidised wire etc.

Spoke with several bike riding mates and the common advice was that the crappy petrol we get these days fouls plugs and they advised running a hotter plug. One mate suggested a new on the market fuel additive that will clean up the carbon deposits in the combustion chambers and I'll be giving that a try out tomorrow.

One mate's first response was valve guide seals, which I know are on the way out and have been flagged for replacement as soon as I make up my mind to do the rings. That depends on how far I want to let the compression drop before working on the motor again. :? Until then I am using an oil additive that keeps the seals pliable and thickens the oil so it doesn't squeeze past them so much.

The other carby set I was working on has been on the bike and off again three times in this week, but I just can't get them running smoothly. The bike has a 4into1 header with straight through can and the existing carbs have larger jets. Perhaps the standard jets in the other carbs just don't give it enough juice - which seems odd considering that it's running rich. Perhaps I haven't cleaned them up sufficiently and something is blocked up somewhere. So I'm back on the old carbs but they have had some TLC this last week.

On top of all that I put in a new plug for #2 pot and the bike decided it liked it. (All plugs are less than five thousand kilometres old) Now's it's running OK again. This weekend I'm riding both days so with the clean-up stuff in the tank and leaner carbs, and with several hundred touring miles, I hope that the motor comes home happier than it was last week.

Best wishes
Kim
 
glad it worked out i had a simular problem with my 850. I was having trouble with the petcock and flooding one cylinder. After i rebuilt the petcock another problem arose with one cyclinder not fireing consistantly. I changed the plugs...no help, after swapping the wires i found it was a faulty wire. Now it runs good again :D
 
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