Just one cylinder or both? Happen all of a sudden? Could be a number of things. I'd check air filter first. Could be a weak spark as well causing the mixture to not fully burn. Other possible causes are incorrect float level, float stuck open causing level to get to high (make sure to check your oil for fuel), jet dropped out. I don't know anything about these carbs, do they have a choke? If so, could be stuck closed.
What ever you do, make sure you just check one thing at a time though.
when the plug fowl its only one at a time....but not always the same one.....and yes its fuel injected.....when I change the plug it will last for a few days and then the same story all over again.....
take the fuel injectors out, and place them in the other cylinder, (injector from the front cylinder to the rear cylinder, injector from the rear cylinder to the front cylinder). if the problem follows the fuel injector, the fuel injector is bad, if it stays with the cylinder, then its prob a pcm problem. the fuel injectors rarely go bad so im wondering if it could be a coil/spark issue.
This is going to sound odd, but fueling can sometimes be counter-intuitive with respect to FI. If the fuel pressure is very low, the spray patterns will be lousy and can cause poor burning...even fouling as large droplets are getting into the chamber vs the finely atomized spray we desire. While troubleshooting the problem, a fuel pressure check should be on the list....at least to eliminate it as a potential cause.
Weak spark was my first thought reading this as others have mentioned, but it is unlikely that both coils are defective at the same time...unless the system voltage is very low. Even if the battery is good, making sure the charging system is up to snuff is another thing on the check list.
You're sure the fuel hasn't been contaminated? Solving the puzzle you have is one of the more satisfying things an owner can do with their bike. Good luck!
Thanks for all ur help...I charged the battery full two weeks ago and last Sunday again just to make sure its not the battery and sofar with a full battery every week its going ok...I really think u guys were right about the battery and the charging..thanks