400ex cutting out

[honda729]

I have a 99 400ex mostly stock, it runs great for most of the time but sometimes when i run wide open and my back tires leave the ground, when i comes back down it stalls out like im in too high of a gear. It only does it sometimes and tends to do it on long hill climbs. I havent tried a new jet yet but if it is a jetting problem why dosent it cut out all the time?

[Rip_Tear]

first what does mostly stock mean? is there anything done to the motor/carb/intake...

maybe you just need to gear down? clean the air filter...?

[honda729]

cobra slip on, uni foam filter.

it runs great most of the time and i can do the same thing twice, once it will cut out and once it will run fine. i have plenty of rpms and once it does cut out i have to pull the clutch in and pump the gas to save it, sometime that dosent work and it will still stall out as soon as i let the clutch out

[Rip_Tear]

Did you jet it after the slip on and air filter? Those are probably enough to throw the jetting out. Even just at top end the jetting could be off enough to make it stall out if it's not getting enough fuel. Since it doesn't sound so bad you probably only need to go up a single jet.

[honda729]

ill try that, I dont know if it has been jetted or not i bought it this like this. the guy said it was but he also tried to tell me there was a 440 kit in it

[QuadManiac]

I think your float level is too low, so on long WOT climbs, the float bowl level drops and you end up starving for gas... pumping the throttle to recover explains it - your throwing some gas from the accelerator pump to overcome the loss from the main jet.

Adjust the float a little higher and I'll bet the problem goes away!

BTW, you may be running lean, due to the free flow mods added to the quad, and jetting is a good idea to prevent damage due to overlean conditions. BUT, that doesn't explain the loss on long, fast climbs. Float level does, IMO.

Good Luck!