i have a 2000 400ex that i just bought a couple weeks ago , it keeps bogging down at 3/4 to full throttle in every gear. it wasnt doing this until today after i changed my oil and cleaned my air filter and air filter box, i dont understand why it would be doing this all of a sudden. the only aftermaket part on it is the k&n air filter with a prefilter. i thought it could be the jets but it wasnt doing it before today so i dont think its that.

 

I just went through this same thing with my wife's Polaris.

Sadly, there are just too many things that could be wrong that have nothing to do with what you did. It could just be coincidence.

If you're carb experienced, pull the carb - dismantle it and give everything a thorough cleaning. It could simply be that a bit of crud has gotten lodged in there somewhere.

Once you know it's not that, then we can start checking on other things.

 

try adjusting the valves

 

3/4 to full throtle is where the main jet kicks in. If it happened spontaneously, it is probably a clogged jet. Could be bad fuel or the K&N. I don't care what K&N lovers say, they do pass fine grit...I know from 1st had experience!

 

If it started after you serviced it, then you need to take a good look at the air intake system, check the airbox to carb seal, check the filter to airbox seal, check the airbox lid seal and make sure the airbox lid is installed correctly. Did you oil the filter properly? If the K&N is not properly oiled it will pass to much air. I agree with reconranger on the K&N filters, I dont like them for offroad machines.

 

thanks alot for your help. the filter was the problem, i oiled it some more like you said and it runs perfect.

thanks