Okay here is it I have a 2002 400ex, it is a 440 big bore with Yoshumere full system stock air filter with K&N air box lid,
The pilot jet is 38....my issue is I can not not get it to start off starter or idle if I bump start it unless I turn the idle up bu then it's a really high idle.....it runs hard and really strong take almost nothing to get it to fire right up with a bump start maybe a jogging pace it turn over 3 or 4 times hits the firing stroke with the throttle open it fire right up and doesn't have any issue what's soo ever till you pull in the clutch and let off the gas it just dies, you have to keep on the gas and rev it up and work the throttle to keep it running....you can come off the low end really hard and it revs up just fine not ruff or hard to get going.....I don't know what else to do anything will help soo please reply ASAP....also just bought 42 pilot jet hook to install and adjust the mixture screw to 3 & 1/2 turns out maybe it will finally start

 

sounds like your pilot jet is plugged/clogged. pull it and clean it.

 

I have already done that I even went up to a 42 pilot the main 170 do you think that would have anything to do with it.....it still won't idle other than when you turn it up really high to wear the throttle is a little open

 

Did you do an compression check with an gauge?

 

is the choke assembly stuck in the "engaged" position?

 

papa hogg, do you think that it ain't pulling enough vacuum due to the larger orifices of the jets or the compression is starting to wane and lose the necessary vacuum for the carb?

 

Wouldn't it have trouble running period if the compression was to low....because the piston and rings are bed brand new head gasket just resealed all the valves are in spec

 

Will run with low compression just hard to start with starter..If you have to push off to start IMO you forcing the fuel and compression to ignite instead of starter doing the job for you.Just an ideal to start trying to figure out atv problems..No problem here at all....Good luck