[dplantz]

2004 CRF250X
Over the weekend, I pulled my tank for the first time ever, to make it easier to change out the spark plug for once.

I found an air hose that sits right above the spark plug that I cannot figure out where it goes. I can see no connection on the tank, on the area around the head, anywhere near the carb, etc... Appears to vent out under the bike. What is/was this for?

[Back2-2]

You may have found the formed line from the "T" to the transmission vent ?

Fairly small diameter 1/4" or less ?

It could also be crank cse vent line that someone removed from the head to the air box and routed it up and around the top of the valve cover ?

Larger diameter 5/16" or so ?

Try to follow it back and I'm sure you will see what and where is goes.

[dplantz]

Its is a small rubber line that has an L bend to it and just sits above the spark plug

[Back2-2]

Just guessing but that sounds like the trans vent tube.

[Leardriver]

Does it plug in to the top rear of the cam cover?

I've never changed the spark plug on any of the 15 CRF's that I have owned. They last forever.