WR400 Splutter Problem

Hi i have a 1998 WR400 and have a problem with spluttering. when accelerating it splutters and then suddenly goes, if you keep the bike in high revs changing through the gears it dosent seem to splutter. If you try to accelerate from low gear it splutters.


1st. I'd jet the pilot circut to make sure its not clogged and the fuel screw is adjusted correctly.If that doesn't correct the problem then your next most likely candidate is your AC pump. If the bog is a fairly new condition then there's a good chance that your diaphram may have corroded or have a small tear in it. If this has been happening since day one then the AC pump timing may be off. There is plenty of info here at TT to find out how to adjust it. Good luck.

are you dumping the throttle or rolling it on

at our last yamaha class they said it was normal when you dump it

only evident at 1500-2500 rpms

sounds like to big of a main jet or if your needle if adjustable,needs to move the e clip up one notch on the needle.

so you can lean out the fuel being burned. i think the pilot jet is for idle plus some throttle.maybey it's a little to big for you temp. and elevation.

Where on the throttle does it sputter?

If it's within the first 1/4 it's the pilot circuit - too rich. Smaller jet or adjust the fuel screw (turn it in 1/8th of a turn at a time.).

If it's above 1/4 and below 1/2 try dropping the needle 1 clip before changing out the main jet since it seems to run fine in the higher rpm's.

If it happened suddenly, try a new plug.

Check the accel pump shaft. They get corroded and don't move.

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