400ex problems

[ridina400ex]

I recently put a twin air filter on my 400ex and cut holes in the airbox. Cut the exhaust baffle off and changed my main jet to a 52. It ran fine when it was cooler out, but now that is it warmer it sputters and doesn't run good at all. I changed the jet back to the 48, and still no difference. What do i do now?

[cals400ex]

i would clean the air filter, run the 152 mainjet, make sure you don't have any air leaks in the intake system.


also, take carb cleaner and remove your jets and spray the heck out of the carb.

[ridina400ex]

the air filter is brand new, only been used once, and its still clean. and as for the leaks there seems to be none, like i said the quad ran good a couple of weeks ago.

[daimon1054]

Re-jet! It tells you how in the tech section of the board.

[cals400ex]

i assume you oiled the filter properly?

[ridina400ex]

I'm not a moron, i did oil the filter

[cals400ex]

i never said you were a moron. the K&N's come preoiled but the foam filters don't. i was just making sure. we all have those monents sometimes. i can guarantee you many of people can't get their bike running because either choke is in the wrong position or the run switch is off.


like i mentioned earlier, i would try cleaning the carb out.

[PismoGuy400]

yea last week i pressure washed my bike and went to give it a little ride to dry it.. it wouldnt start.. i tried everything, then i look on the bench theres the kill switch tether i about wrapped it around my neck, we all have some moments when we feel stupid.

[cals400ex]

Originally posted by PismoGuy400
yea last week i pressure washed my bike and went to give it a little ride to dry it.. it wouldnt start.. i tried everything, then i look on the bench theres the kill switch tether i about wrapped it around my neck, we all have some moments when we feel stupid.


thats exactly what i was getting at.

several years ago, well before 400ex's even came out, i was riding my trx300 and it started missing and wanted to die. i had no idea what was wrong. at the time i was only 13 or so and of course i didn't know a ton about quads. i drove the bike home keeping on the gas to keep it running. when i pulled it in the garage i realized i had the choke on. ran great when i turned the choke off. :o
i guess it was a little rich when the bike warmed up. :)

[ridina400ex]

ok sorry i didn't mean to offend anybody, but what i'm getting at is that i have checked everything and it all seems good. Its not like my quad won't run and i gave up on it within 5 minutes and came running to my computer.

[daimon1054]

Once again JET YOUR QUAD! When the temp changed the density altitude changed and that changed you jetting needs. In the cold you were more than likely lean and now that it heated up you are way lean.

[ridina400ex]

I wouldn't be lean, i would be rich

[cals400ex]

Originally posted by daimon1054
Once again JET YOUR QUAD! When the temp changed the density altitude changed and that changed you jetting needs. In the cold you were more than likely lean and now that it heated up you are way lean.

as the air gets colder, it becomes more dense. thus you are taking in more oxygen. you compensate by increasing the size of the jets. when it gets warmer, the air becomes less dense and you need to go smaller on the jets.