hey peoples, i need some info here. im having issues with my 99 900RR, the problem is that my spark plugs are getting BLACK, and these are new from a dealership, i have an Keihin FCR39 carburator on it and i wanted to know why this is happening??? and how can i fix it.

 

Maybe you have oil fouling the plugs.

Somehow oil is seeping into thepiston area. How many miles on the motor?

Bad piston seals maybe?

 

bike has about 15k miles on it. when i took one of the spark plugs out, it did have residue not sure if it was oil or gas, forgot to smell it, but it didnt look thick enough to be oil, not sure, ill look into it.

 

What is theeffect to your engine??

 

http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm

Sounds like it's rich--too much fuel, not enough air. What kind of air filter is in the box? Does it need replacing?

If it were me, and nothing else was different on the bike, I would yank those 39's and buy a good set of used OEM 38's.

Otherwise, read up on how to adjust fuel-to-air mixtures (jetting) on carburetors and give it a go...

 

ya with bigger carbs you prolly need to lean it out a little try a jet kit ( if you can find one for those) and try that also what was the bike doin to make u pull the plugs?

 

Keep in mind, what you were doing immediately before you shut the engine off. Were you letting it idle? Or did you run it at WOT and then hit the kill switch and then pull the plugs? But I agree, intially, it sounds like it's to rich.

 

oooooh, thank you for thet diag site, yeah the bike is running way too rich, ill have to adjust the air-fuel jets apperently.

the plugs got fouled rather quick though, because yesturday i just put the bike back together from the same problem before,
and i was running it idle for a bit to let it warm up and what not, and it kept turning off after 1-2 mins on idle. It seemed as
if it were losing power when it happened and so after maybe 20-30 mins of me turning the bike on after it shut off everything,
it didnt want to turn back on so i took out one of the plugs to find it fouled =/.

does anyone know where i can maybe get the right AFR settings for this carb ?

 

Carb tuning is almost a black art. LOL. It is a lot of trial and error and it takes a lot of time to get perfect.
He is right, without an A/F ration sensor (such as on a dyno) you have to run the bike at WOT and kill it, then look at the plugs to see how they look. They should be a milky brown when the mixture is right on. That will get your main jets set right, but may not fix any part throttle issues (if you have any). Your intermediate jets and to a certain extent your idle jets will play a factor in the part throttle response as well as needle height.
Again, it takes time, but it's VERY hard to beat a perfectly metering set of carbs.

 

aint that the truth man all i had was probs when my brother "upgraded" his old CB700 with bigger better carbs and it ran like crap for the longest time until we finally got it running right with a pair of OEM carbs.