'99 YZ 400 Air box problems?

Heres the story, my bike will start just fine but when i put it into gear it will die as soon as I give it a little gas. i keep digging junk from the drain bolt in the crab but i keep getting more and more. i even sent the carb to the bike shop and they deep cleaned it. they told me found a whole bunch of junk and were surprised it even ran. so i went home and cleaned out my air box till ther was no more dirt and i also cleaned the air boot. my air filter wasn't too dirty so i just left it. i get it back together and go ride at a pretty water infested track and it starts doing the same thing. so i quit riding in the mud and it runs fine. so tonight i pressure wash it and check the drain bolt to see how much dirt was in it. it was filled up... my dad and i think that its getting in through my airbox cuz the guy who owned the bike before me took off the top of the airbox ( the cover). anyways just wondering what you guys thought? i also thought dirt could be getting into my engine through the breather hose for the head. but i am really worried cause i think there is a good chance my engine may seize. i mean it still has great compression and power but it worries me. what do you think? this is the first bike i bought by myself and i am really frustrated that its running this way. where can i get an airbox cover?

any suggestions or replies would be appreciated. thanks


Is there somewhere on the carb side of the air box where it is letting in unfiltered air? Possibly one of the boots is cracked and you don't see it? Maybe the boot isn't on as good as you think it is?

Just some ideas.


both my dad and i checked to make sure the boot was secured on. but i didnt check for holes. that may be possible but i did clean inside the boot and it didnt seem to have one. also the amount of stuff was just unbelievable. i think the dirt may be gettin through the side panels and the filter because i dont have the cover for the airbox.

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