07 yzf450 carby problems

[Yamaha mad]

Hi all,

My mate has an 07 yzf450 and is experiencing a problem with the carby....as he is illiterate to computers I'm here to help him out if I can. His problem is that at about 1/4 throttle is has a bad splutter and it's driving him mad....it starts easy and idles and revs crisp but just has this splutter that won't budge...he's tried new jets and give the carb a good clean and going over but can't seem to fix the problem. Has any1 experienced this problem or know how to fix it. Cheers for any help.

[FORMA MOTO]

Replace the slide plate seal (prevents slide from sealing)

Replace the needle jet (it ovals when it wears)

Put in a good fuel screw like R&D and read up on how to adjust it.

Valve adjustment

New plug

[grayracer513]

Be certain that the slide plate is installed right side up.  This is a common mistake.  The "square" side with the hole near the edge, NOT the rounded side, goes down.  Also be sure it's not cracked or missing a corner. 

 

Most of the time, the slide plate seal is fine.  It will come out of its place swollen and wavy from the fuel, but if you leave it out overnight, it will usually return to its normal shape, and can be reinstalled without any trouble.

 

If the problem persists, try unplugging the TPS (throttle position sensor) on the carb.  When these get flaky or have been moved without calibrating them, they can cause the exact problem of which you complain.  If the stutter goes away, it may not mean the TPS is bad.  Check its resistance at both ends (open and closed positions), and watch the VOM as you slowly move it through its entire range.  The resistance should rise and fall smoothly and consistently.  Any glitches, dips, spikes, etc., are bad.