Ok guys heres the deal...i need your help... I have a 99 YZ 400 F and im having problems with the bike bogging over bumps and jumps, If i hit a set of whoops i can hit the first whoop hard but then the bike bogs when i go to give it some more juice to make it through the section, it sends me right into the handlebars...no fun! then over jumps it likes to bog mid air and on the landing...i thought maybe it could be that i was hitting the sections in to high of a gear so i dropped down a gear but it would still do it but it wouldnt be as bad...I feel so unsafe on the track now because i cant control the bike mid air or gas it when i land:thumbsdn: The only thing i have messed with on my carb is i put in one size bigger of a pilot jet to help with starting and i messed with the fuel screw a little bit but none of that helped with the bogging. The bike shop suggested i get the carb checked out for worn parts but i had the bike shop tear it down last year and clean it out...still didnt help...maybe the parts are worn now...i dont know...they also suggested the Quickshot Accelerator pump...Im thinking about getting it but wanted to ask for your guys input first.

Have you tried changing back to the original pilot jet ?

If this cures your problem you have the answer as it is possible the pilot jet is now too large.

Also carnurettor cleanliness is vital, could be you have some dirt in the passageways. Stripo the carb and blow out all the passages. Also flush your tank to ensure there is no dirt in there.

There should not be any need to consider adding after market components to cure this problem.

My 400 has stock jetting and throttles just fine.

Check your floats to make sure there set properly. Change back to your original jetting, and clean then hell out of the carb.

Float level should be checked first. Then be sure your carb is clean and jetted right, and that the idle mix is set correctly.

After that, you mighty want to look into this old trick:


Could maybe be that your accelerator pump diaphram has failed?? Or is seized?

Start with cleaning the carb, checking for broken parts, and set the floats as per the manual. If that doesn't fix the problem, and it has only started doing it since you changed the pilot jet, try going back to stock.

Throwing aftermarket parts at this sort of problem only leads to a lighter wallet.

Just my .02 cents and YMMV.

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