01 Oil in the airbox....

Okay, here are the symptoms...

Oil is coming into the airbox off the vent line out the back of the case,

Its a rebuild with 1k on it

101mm 10.5:1 wiseco

Hotcam stage 1

stock jetted carb

k&n (not over oiled)

white bros e seires pipe

Not a wheelie rider

My buddys 400ex did the same thing after build but stopped after a min, and we did a race build on it 11.5:1 416cc

I'm stumped with this thing.

I know i need to do a carb rebuild on it, vacuum diaphragm, but other than air fuel mix he's fine

no airbox blockage

not smoking out the pipe at all except when it loads up on fuel, then its just black. 

I dont know what psi it should be on compression with these upgrades, but it seems the rings are seated

I've got way too much money in the bike to start over. somebody please shed some light on this for me!!! :banghead:


Drain all the oil out of it,,,downtube and crankcase.........measure it,,you should only have 2 quarts or a little more,...


Either you have blowby or over filled the oil...


Unless someone removed the oil separator,is it still there???



Edited by brianhare

It was about a quarter qt low. And what is this oil seperator? I've never overfilled this thing

Should be a canister on the left side attached to the frame rail and blocks view of the carb....some people remove it when removing the emissions,some sites call it a charcoal canister,,,,,,,,,but it`s actually an oil separator...a hose from the crankcase goes into it and then one goes to the airbox,,,,,,,,,,,removing this oil separator and just running the hose to the airbox can cause oil to flow up the hose into the airbox..



Yeah.. its not there


Mine was missing the separator when I bought it as well. I had the exact same issue. Airbox would be a greasy mess in no time. I ran a longer hose up to the top of the airbox so it sits inside the airbox and capped the hose with a small K&N filter. Problem solved.

Thanks man! Will try that!

And for Gods sake man get yourself a decent carb. If the carb needs work why dump good $$ after bad. Get an fcr carb from fleabay and do the jet mods described here. The bike will thank you and run much better.

Thanks for the advice man, although can you give me a little more info on what carb to get?

Thanks for the advice man, although can you give me a little more info on what carb to get?

Look for an FCR-MX from a CRF250 or 450. The 41mm carb only came on the CRF450 for a year or two so they are harder to find, but the smaller bore FCRs seem to work just fine on the XRL.

Thats all i did when the smog equipment got ditched. I also ran a small k@n filter on the crankcase breather tube. Works great.

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