hand full problem

I've got a problem.

98 yz 400, new plug, clean air filter, oil changed, cleaned the carb, all regular maint.

Every time i'm out riding, when I grab a handfull she falls on her face. Sometimes it will stall, sometimes not. This bike idles fine, sounds good and all, but when I need that handfull & its not there, big trouble..

Hope someone can help.

Sounds like a clogged or partially clogged main jet. Is the accelerator pump operating correctly?

Check your accelerator pump. This past weekend, my '01 did the same thing. After putting in a new plug and messing with the fuel screw for about an hour, I noticed my acc. pump arm wasn't moving with the throttle wheel. Took the carb off, unbolted the acc. pump cover and found dirt. Cleaned it with carb cleaner and it was fine. Took about 15 minutes.

Ive checked the jets, and cleaned the acc. pump.

I realize you cleaned the accelerator pump, just remember the non fuel side (top)is the side that fills with dirt. Also make certain the pushrod is not sticking. I've worked a '98 that had dirt jamming the diaphram and also the pushrod, both had to be cleaned to get good operation. It could also be that you have not bled the pump chamber full with fuel. Did you ride the bike or test it on the stand?


Did you verify that the accelerator pump is squirting fuel? You can check by removing the subframe and airbox. With the petcock on and looking inside the carb venturi, twist the throttle and see if fuel is squirted toward the throttle valve(slide). This would be a good time to also check to make sure the the squirt of fuel misses the slide plate and should have a duration of about .3 seconds. Yep, it's just a quick squirt. It's very important that it barely misses the slide plate or you won't get the benefit of this little squirt of fuel.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now