skipping???

[flaneledholes]

OK im gonna be descriptive... I went and bought my 400 5 days ago... It was runnin rich so I took the spark arrestor out and I thought it hepled but it still stumbled a lil bit at 3/4 throttle but I was fine with that... Well me and my bud went and built a pretty big jump and I turned the quad off after hitting the jump bout 15 times... I went to pull out and it was sputtering all the way home Im talkin bout 1/5 throttle and on it would not go any faster than 1/5 throttle...I turned it off let it cool for bout 3 min. and it was ok... My ? is why did it do that???Any suggetstions on what to do??? How about going on ahead and grinding the welds would it help the rich problem???

[Striker49]

Originally posted by flaneledholes
OK im gonna be descriptive... I went and bought my 400 5 days ago... It was runnin rich so I took the spark arrestor out and I thought it hepled but it still stumbled a lil bit at 3/4 throttle but I was fine with that... Well me and my bud went and built a pretty big jump and I turned the quad off after hitting the jump bout 15 times... I went to pull out and it was sputtering all the way home Im talkin bout 1/5 throttle and on it would not go any faster than 1/5 throttle...I turned it off let it cool for bout 3 min. and it was ok... My ? is why did it do that???Any suggetstions on what to do??? How about going on ahead and grinding the welds would it help the rich problem???

If its running to rich your jettin is set to high. Need to go down 1-2 in the main jet?

[brian400ex]

Check your plug and see what color it is. If it is white go up in your jetting. If black you are running rich. Go down in your jetting.

[phatswinn]

yea check the plug then re-jet

I believe what happened is, you said it would stumble at 3/4 throttle, that is all main jet there. a stumble would suggest a rich condition and you continuing to ride it that way most likely fouled the plug which is why it wouldnt run very good on the way home. the pilot of a 400ex is known to be very lean so thats why it would run till you opened the throttle up and got out of the pilot circuit and into the needle circuit.

some fuel wont color the plug to give you a good reading so dont rely on that completely.

by pulling the spark arrestor out you opened the exhaust a bit which made it not quite as rich as it was before. opening the exhaust more by grinding the welds may help some but doubtful there is a big improvement. did both of these mods to mine and the combination of them plus removal of airbox lid,choke, and adding a new high flow UNI filter may a big difference.

If you have the airbox lid on then try taking it off. the person before you may have jetted it to run without the lid or something.

[skemp]

The main could have fallen out and caused that over 1/5 throttle bog. Since it was running like crap before that, it could have been loose and just hanging there letting a bunch more fuel in until it finally fell out. Take the plug out of the float bowl on the carb and I wouldn't be surprised to see the main jet laying there.