Acouple months ago i bought a mint shape 1990 CBR1000F for $1000, except it hasnt ran in 2 years so the carbs needed work. i brought it in to get worked on, and they got it running, except when u either give it full throttle or it goes above about 5000rpm, it starts to sputter really bad. it has a full system vance & hines exhaust, so the place i brought it into thinks that it just wasnt rejetted for the pipe. but i called the pipe company, and they told me what main jets i needed, and today i took the carbs apart and it has the right jets. so i was just wondering if anyone had any suggestions to what the problem could be? it runs fine at low rpm, but i would love to be able to rev itout![/align][/align][/align]

 

The only thing that I can think of (and it may not even apply) is that the ignition advance isn't working. What I would do is to download the service manual https://cbrforum.com/m_123412/tm.htm (Thanks Trips) and check out the troubleshooting section

 

id replace the fuel filter, check fuel pump also, definatly a fuel restriction problem

 

Yes the stock jetting will not cause sputter even with a free flowing system but the needles may be needed to raise, especially if you have a K/N filter.

If you still have the carbs opened, check the following:

- Remove the floats and check that the little spring loaded pin at end of float valve is not stuck. It is just to push on them if they are stuck, do it several times and also use WD40 to help cleaning.
- Remove the float valve seats and pull out the nylon mesh filters. You can discard the filters if you put an in-line filter on the fuel hose.
- Check that the rubber tips on the float valve pins are fine, replace them if they look not to seal properly.
- When assembling the carbs, check and set the float height to 9 mm
- Also blow brake cleaner or CRC true all passages in carbs
¨- Adjust the fuel screws 2 1/2 turns out from bottom position.
- Don’t forget to put back the rubber hats for vacuum measurements.
- Check that the intake rubbers are fixed by screwing the clamps a little.

If the problem remains, you have to raise the needles. It is just to remove the top cover on carbs, lift up the throttle unit and unscrew the needles with a 8 mm socket. Then rise the needles by a M3 washer and test run. If the bike runs better, put in another washer.

The problem can also depend in a cracked air box making the bike sucking air before the air filter that will give to little vacuum. If the air box is cracked around the tubes to carbs, clean it with some degreaser (e.g brake cleaner) and seal the cracks with silicone.

 

alright thanks a lot guys, ill have to try this out