No throttle response 00' WR400F


Check to see if your accelerator pump is working. The rod on the side of the carb can get dirt etc. in its passage. After sitting its very possible to lock up. No squirt as well as to much both cause off idle bog. Sounds like you have covered must other solutions.


If I would have paid attention, sounds like you have done this. Do you have squirt?

Engine falls flat on its face when throttle is whacked wide open, or opened abruptly at low rpm. I have checked / cleaned the following: Sprayed contact cleaner through all jets and passages, including air jets in venturi, cleaned and inspected accelerator pump, and air cutoff valve, checked the float hieght, checked for air leaks around carb, and dumped old fuel from gas tank. The bike is running stock jetting at 1000 ft above sea level.

The bike idles fine and runs fine at steady throttle settings all the way up to high rpm. The bikes sat for a couple of months while nursing injury. Noticed problem on first ride after down time.

Have attempted to fix with all methods listed above, and now in need of help and ideas.



It squirts pretty good, but when I pulled it apart it was dirty. I will be keeping a closer eye on that in the future.

I just finished taking the carb apart one more time, to recheck the slow jet. I started thinking that when I sprayed cleaner through the air cutoff valve the cleaner was running out the slow jet, and maybe I sprayed junk down into it. I pulled the jet out and cleaned it again because it didn't look great. The bike is running a lot better, but still is not perfect.

I have a 42 slow jet in the bike, and Yamaha of Troy lists a 45 as standard. Now I am thinking I might have always had to lean of a slow jet in the bike.


Have you changed the fuel pump screw...if my memory serves me correctly it should be set at 3/4 of a turn out (CCW). This will cause a hesitation right off idle if not adjusted properly.

Have you ever removed the spark plug cap from the coil wire?

This caused me alot of grief. I reinstalled it by pushing it back on but it must be turned on because there is a spiral wire inside the cap that "threads" into the coil wire to make a good electrical connection. Without turning the cap on the wire my bike ran just as you had explained.

Good luck!

Blow the cleaner thru the passages in the carb body....they can plug up too.

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