HELP! CUTTING OUT OVER BUMPS!

I have a stock 99 YZ400F with FMF powerbomb

and stock exhaust. I ride at 5,000 to 8,000

feet. Jetting is as follows:

170 main

45 pilot

Needle dropped one position

Air screw two turns out

The bike runs awesome except it cuts out over

bumps and jumps. Please help!

Jay

Does your bike cut out on every little jump and bump? Or does it vary? I had a XR400 which had the same problem you are having...after many hours of jetting frustrations, I came to the conclusion that my float was sticking open and sometimes shut :) ! So I took my carb off and gave it some treatment with carb cleaner and compressed air :D ! I also checked my float level (which was fine) and the bike ran great afterwards!

I also have heard of guys with 98-99 YZ400's having dirty accelerator pumps...I have not had this problem so I cant help ya on this (but im sure others can like: Boit, Hick, James Dean, mikeolichney, etc since they are experienced with the YZF's carb) !

If you have never taken the carb before...just lay out some white towels on the floor of the garage or workbench and start disassembly (sometimes it gets hard to see those little parts)! And just follow the manuals procedures (since it is pretty straight forward on the directions)! Hope this helps you solve your annoying problem!

Garrett

------------------

I get my kicks on a 2001' YZ426!

Friendswood, TX

Thanks. I'll act on the advice and repost tomorrow!

Originally posted by motoman393:

Does your bike cut out on every little jump and bump? Or does it vary? I had a XR400 which had the same problem you are having...after many hours of jetting frustrations, I came to the conclusion that my float was sticking open and sometimes shut :) ! So I took my carb off and gave it some treatment with carb cleaner and compressed air :D ! I also checked my float level (which was fine) and the bike ran great afterwards!

I also have heard of guys with 98-99 YZ400's having dirty accelerator pumps...I have not had this problem so I cant help ya on this (but im sure others can like: Boit, Hick, James Dean, mikeolichney, etc since they are experienced with the YZF's carb) !

If you have never taken the carb before...just lay out some white towels on the floor of the garage or workbench and start disassembly (sometimes it gets hard to see those little parts)! And just follow the manuals procedures (since it is pretty straight forward on the directions)! Hope this helps you solve your annoying problem!

Garrett

I have not had this problem on my WR, but did on a previous bike. The float level increased with hard square edged impacts that were in long stretches. You may want to lower the float level to 1mm below stock.

James

You might also want to check that your carb vent lines are not kinked or clogged with dried mud....only takes a couple of minutes and requires no tools. Sometimes, it's the simplest of things.

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