wierd sparkplug problems

OK here we go. After i put a new sparklug in i ride about two rides and then my bike starts running wierd. loud poping and what not and not much get up and go. So i check my plug and it is all sooty and black. i changed the plug and it goes fine for a few more rides. It hasnt done this before but i did put on a new pipe this winter. All the riding i have dont with the new pipe is great till it the weather started warming up. I am at 2500 feet and ride up to 5000'. My jetting is 170, 45, needle 3rd position. I am assuming that wiht the blackness of my plug i am running rich. Or is there something i am doing wrong. Do i meed to go leaner on the main or what. thanks guys . I tried a search but i didnt find what i needed. Thanks.


Fouled plugs are (1) wet fouled, (2) carbon fouled, (3) oil fouled. (1) and (2) are caused by the electricity flowing from the center electrode to the plug threads across the center ceramic instead of across the gap--no spark. Oil fouled plugs insulate the center and top electrodes.

Wet fouled plugs can be cleared by drying them, either through a thorough flooded start drill (twist wide open and hold, push through with comp release 15-20 times, release throttle, and start) or removing and blowing on plug or sitting in sun. A carbon fouled plug is almost impossible to thoroughly clean. You have to scratch/scrape off a ring of carbon around the electrode (or have access to a plug sandblaster) just to get it to start but it won't run well at mid/high RPMs.

A not quite carbon fouled plug (one with some carbon on the center electrode) is far easier to wet foul than a cleaner plug. This is almost like a combination fouled plug. Dry thoroghly and it might work.

Carbon fouled plugs are caused by the last ride. A wet fouled plug is fouled since the last ride or while trying to start. This is why the caution about not twisting the throttle while starting. I'm assuming you have this down pat and haven't changed your starting drill or anything between rides.

That leaves being (1) too rich somewhere or (2) a weak spark. I'm assuming your jetting has not changed. The things to adjust for would be your pipe and the weather. Going to a more open pipe would cause a lean condition (i.e., you would enrichen to accomodate it). That is not it. It is probably cool now which is leaner than the hot last summer (again, you need to enrichen for cool weather) so that's not it. So I'm ruling out jetting (in the normal tuning sense).

The most likely thing is oil from the air filter plugging the pilot jet, the pilot air jet, or the main air jet. The pilot is the most susectible. Plugging the emulsion tube portion of the pilot will cause it to run rich. A carb cleaning and a new 'not too heavily oiled' airfilter would fix this.

Next most likely would be a weak spark. This would be caused by either the CDI, stator, or coil. You can find a 'bad' stator or coil using the electrical checklist. Ignore small out of spec conditions, they would have to be way out of spec to cause this. Swapping know good parts is cool but you would have to do it for at least a couple of rides. The weak spark isn't weak enough to not spark if this is the case, it's weak enough to have incomplete combustion and run cool enough that carb builds up on the center ceramic.

I didn't mention that some gas and some gas additives can glaze the spark plug, causing a poor spark. Are you running gas that sat all winter? Unlikely but worth draining. Even the same brand has different seasonal blends. If it is the gas, brightening the gap with a plug file, emery cloth, sandpaper, or even a dollar bill would clear the plug. It's worth trying next time it happens. If cleaning the gap helps, change gas and brands.

If you want to avoid the problem instead of fixing it, (1) run it harder, being hotter can keep the carbon burned off. (2) Try a CR8E if you run a 9E, the 8E is some hotter. (3) Try a different plug tip profile like the EK. (4) Try a precious metal plug like the EIX(? ERX).

Good luck,


Way too rich on the main jet for your elevation!!!

I would try a 160 main jet and a 42 or 40 pilot jet and then fine tune with the pilot screw. My $.o2.


Do the easy thing First. Close the fuel screw on the bottom of your carb...Open it 1/2 turn and try it...(Check) your Plug. Should be dry...Open the FS 1/4 turn increments until the idle and throttle range are smooth. Go out to the point at which you get 2 full turns on the FS if needed. If you have to go more than that then start changing your PJ first. Chances are that your MJ are fine. Most fouling occures on the PJ. Unless you are running mach 4 with your hair on fire most of the time, your going to be on the PJ much more than the MJ.

Anyway, give the FS a try first and let us know the result. We can better assist you with one piece at a time.

Bonzai :)


Unless (A) your jetting was poor and fouled plugs last summer, (:) you've changed something that we didn't hear about, or © some environment change occured that would dictate leaner, I wouldn't start with the jetting. In fact, I would always recommend a clean carb when starting to jet. Trying to jet away a glob of filter oil is pointless.

That said, if it weren't all of a sudden, Yamakaze is off in the right direction.

Good luck,


Lots of good info here guys!!

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