Ive got a 04 cbr f4. Great shape, only 5k miles on it. It has a 2 brothers slip on, k&n drop in filter, and the baffels to the intake have been removed. Other than that, its stock. Whenever i get on it hard it feels like the bike is holding back, likes its stuttering and surging a bit; like its not really going like it should be. It feels like i have a 250 and not a 600. I've looked at the carburetors and they look clean. My only other thought is the spark plugs are bad, or the jets are not giving the bike enough fuel to really make it run like it should. Anyone else got any suggestions or had similiar probelms?

PS The exhaust was already on the bike when i bought it.

Mike

 

Is it a F4i or F4 sounds like you might have fouled plug

 

I dont think they made the F4 in 2004, but he's talking carbs so definitely not an F4i.

I had a similar problem with my old F4, but it was fixed with some fuel system work. Carbs may be clean and everything, but the bike may not be properly tuned to handle your mods... filter/exhaust

 

more than likely you need to rejet the carbs.... before spending that cash though install new plugs, and definately put the stacks back on it, they wont work right without them. after doing the cheap easy things then get the carbs jetted if it still wont run right.

 

I was just typing too fast, yeah its an 00 f4, my mistake. What you mean stacks? Could you please direct me to a good website or reputable source? Dont they sell jet "kits" for bikes with aftermarket filters/exhaust? What about my fuel filter? Could my filter be bad also?

Mike

 

you are correct Dynojet makes a jet kit, as well as several others.
For online parts ilike bike bandit.,they have an awesome selectiion.
baffles removed??? i figured you meant the velocity stacks inside the airbox

 

Yeah i did mean the stacks, baffles, whatever the hell you call them lol. One of my buddies removed his and it actually ran better, but i think I will put those back in. They are at a damn friends house so I gata go back and get them. Thanks for the input guys. Its got to be either my plugs or the jets. Cheers!

Mike

 

i am going to put $1 that's you need to get a jet kit. is your fiends bike that took his stacks out of jet-ed?

 

supposedly not, which makes no sense to me either. but if you think about it, if you change the air/fuel mixture and the factor jets are only programed to put out so much fuel, then when i yank the throttle and the bike doesnt go where its suppose to like its suppose too, then bigger jets seems like the only most logical solution...but who the hell knows!!!!

mike

 

Well I can only say that its been my experience that if you make filter and pipe changes on a carbed bike you will have to rejet it.
that being said..... there is always exceptions...just hasnt ever been my luck to not have to do it the hard way lol.
I also have seen carbs not act right if the stack/baffles arent in place because it changes air velocity..speed.
id put them back on and change plugs, then plan on gettin a jet kit, probably a stage one dynojet or factory racing kit will be ok.
they come with instrucyions and specs as well as a tech line, check it out you can probably do it yourself its really not hard.

 

ummmmm........just a thought......... you do have the ram air hooked up right? not being hooked up will cause accelleration issues also

 

If your still running stock jets with your mods, your bike should still run fine, but you won't be making the most power. I bought my bike (600 F3) and ran it for a short time with a filter and full exhaust with stock jetting. It was a little lean, but still pulled strong.

You need the velocity stacks on the carbs. Also you need good spark plugs. I'd suggest pulling the carbs and cleaning them, how did you check them to see that they were clean before? Also make sure your vacuum lines are all hooked up, your ram air and intake is all hooked up, and that your fuel filter isn't clogged, and that the carbs are actually getting enough fuel.

 

yeah, im going to get the stacks/baffles tomarrow. i defnitally never should have taken those out. my buddy with the same f4, same color and same year took his out and had amazing results which is why i took mine out..

Im a newbie at all this carburetored bike stuff so excuse my stupidity!!!!

Gata learn some way eh?

Mike

 

ok check this out.....in my opinion..... the only stupid question is the one you didnt ask dude, no need to apologize.
I didnt look to see where everyone lives, but another factor in jetting would be altitude.... its possible that a bike in one part of the country would run decent with stock jetas and mods and not run worth a flyin rats *** in another...

 

You need new plugs and to clean the carbs.
I know tons of people who run slip on pipes on carb bikes and to nothing to the carbs, meaning no jet kit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ktmoffroad72901 &raquo;</TD></TR><TR><TD CLASS="quote">ok check this out.....in my opinion..... the only stupid question is the one you didnt ask dude, no need to apologize.
I didnt look to see where everyone lives, but another factor in jetting would be altitude.... its possible that a bike in one part of the country would run decent with stock jetas and mods and not run worth a flyin rats *** in another...</TD></TR></TABLE>

You know what I did not even think about it, but the guy that had the bike before me lived in Ashville, NC; aka in the mountains...but everything is stock besides the intake and exhaust tho. What would he have done to make the bike run fine at his altitude or did it just get used to it or something?

Mike

 

F4i's have a pressure sensor in the airbox - and the stock ECU is pretty good (at least for rideability with changes in intake/exhaust/conditions). If you had carbs, you probably would need to make some changes.

Sounds like you've got a spark plug or fuel pump problem