My sons 98 cbr600f3 has a lean condition. It has no power in 5th & 6th gear & wont go over 6k in those gears. It has a 2 brothers exhaust & k&n air filter. My question is what kind of carbs do they have, what is the standard jet size & what size should i get for the mods on the bike. Does anyone know a good place to buy just the jets, instead of a dynojet kit for 120.00?

 

I tore into the bike today. I see they are Keihin carbs. The 2 outer main jets were 138 & the inner carbs were 140. I didnt see anything in the carbs. They were clean. No vaccumn lines were off. The 2 ducts from the airbox to the snorkel are gone. I am at my wits end with this bike. I dont know whether to put bigger jets in it or just spend the money & let somebody fix it? Anybody have any ideas???????

 

there's your problem.these bikes are VERY sensitive to mods done to the airbox/ram air tubes.replace those.jetting sounds about right

get rid of the k&n filter,you're losing power.paper works best.the only time a high flow air filter works well is with a highly modded motor.I have spent thousands on the dyno to learn this.

EMGO makes one for 25 bucks retail,so does Hi-Flow,both are available from Parts Unlimited.

 

Thanks for the info. I will check the 2 local mc salvage yards for the tubes & see if they have a stock air filter for the bike tomorrow.

 

there is one advantage of the K&N or others, they are reusable. The filters from the factory are expensive and can only be used once. I am running a similar setup, a slip on, K&N air filter, and stock jetting. My high speed circuits are pretty good, but the idle circuit is a little lean.I second what kjohnson said, these bikes are sensitive when it comes to mods. Set the bike up to the original setup and that should help. Then other thing is to make sure you have no air leaks in your current set up. I had an issue that was similar and it turned out to be the bands on the carb insulators were all loose. So, look around for any potential air leaks.

 

Kjohnson. You were right on the money. I went to Lees cycle salvage & bought 2 used ducts & M.C. salvage & picked up a good used stock air filter for now. Put everything back together & it seems fine. It pulls hard through all the gears. Thats a bunch for the good advice. I appreciate it a bunch.

 

I got my bike for super cheap because the previous owner tore the bike down and coudln't figure out why it ran like crap. I didn't either for a long time and even had posts about it. But I put them on and it ran awesome.

I just replaced the jets on my bike because it was running rich (Dyno verified). I had 138inner and 135 outer. I put the 135 in the inner and 132s outer. But yours is running rich (Where do you live? Elevation/Climate can affect it sometimes). I have BMC filter, Full V&H exhaust and Factory pro needles. I think I need to shim the needles back one cause it's running rich but I'll throw it on the Dyno next tuesday to know for sure.

Which get hte bike ona Dyno if you can. They can tell you exactly where you are rich or lean and what needs to be done. Just do a Base Run Dyno and do the work yourself. That is what I do with my shop. Infact a lot of shops prefer that and will cut you deals on the dyno because they don't want to deal with carbs after being spoiled by new EFI bikes and their Plug and Play Power Commanders.

Don't get the Dynojet kits. Heard nothing but bad about them. Go with Factory Pro