So I'm removing the smog crap and see most are removing the breather hose from the gear box that goes to the air box lower right corner. Why not leave this one hose in place while removing the other items? One less hole to plug and lets the gear box breath.

 

Not sure but if it acts like a PCV system...which I'm sure it does...then I'd leave it hooked up. Your oil will stay cleaner longer and a slight vacuum will help reduce pumping losses on the piston. At least I know all that to be true on normal cars, maybe it's different on the little 250.

 

This makes little if any difference on the KLX. There were lots of experiments and efforts made with the KLR650 which does have decently high crankcase pressure that can sometimes affect oil consumption. The KLX has no such issue and isn't worth removing. Some of us have opened the airbox hole a bit more by drilling to ease a possible draw that might pull a tiny bit more crankcase oil/oil mist into the airbox, but even this is probably a marginal effect. I had my airbox off several years ago for another modification and drilled the hole bigger. I wouldn't pull it and drill it just for that modification.

 

No idea why in the world anyone would cap off a breather or disconnect the hose from the air box (a bit cleaner air). But some will disconnect everything they can, without a clue what or why, no rhyme or reason. Just the way some are.

I would heartily recommend don't do what everyone else is doing without learning why and wherefore. Learn what you are doing and why.

 

klx678,
Yes I agree and that is why I ask. The only down side I can see is any blow back mist from the gear box getting into the filter but hey, it is already set up this way so it should not be an issue to leave as is from what I see.

 

I disconnected mine and using my leftover PCV hoses - routed it to just out below the shock reservoir, adding a small K&N on the end. Its end cap sits more or less flush with the reservoir, and doesn't stick out from the side.

Not content with that, I replaced the oil fill cap in the clutch cover with a screw in spigot and ran a hose and small K&N up to just in front of the upper part of the air box.

That's why I'm so fast


I caught a mention of some late model MX bike that had a breather spigot/hose in its cam cover btw.

 

Well, you're knowledgeable enough to know to stick a filter on the end. Not everyone thinks that way.

The KLX650 has the breather in the cam cover, blows off oil a fair amount when set up as stock. The breather hose runs down hill from the head to the air box so any and all oil condensation will go to the air box and out the drain. I made up a little breather "box" of PVC tubing and extra coarse steel wool to set up a place to help with heavier mist to condense on the steel wool in the tube and flow down to the head since the "box" is above the cover.

Worked great, no more drips under the bike. Still blows off oil as virtually every one of them does. There is a KLR modification using a PCV valve from a Mazda, but I've never gotten around to trying it out.

I'd love to know if the plan is to try to promote a vacuum effect or a pressurized effect. I'm thinking vacuum, but really would like to know and understand more about it... why? I have thoughts, but never really discussed it with anyone and not sure I have a clue or not.

Any thoughts or knowledge Richard, TNC, anyone? PCV valve and why.

 

Yeah, I'm in the middle of plugging my air injection system now. Prolly not going to do anything with case breather either, but if I do, was thinking just loop a hose from bottom nipple to top nipple on airbox to plug those from being open to outside. The case, I would just run up then out to ground like older bikes did. I'd run up high enough for water crossings.

 

How much blow back mist could there be? The stock set up vents inside the air box and inside the filter. If lots of blow back mist then would it not get sucked into the carb?

Doesn't a PVC valve work in one direction only? Like a check valve. You would then need to know if this hose is a vent or breather.

Maybe I'm over thinking all this but as klx678 says know what your parts do and what the effect may be before yarding them off.

 

Part of the reason for venting to the air box is to suck in the fumes and burn them - pollution control. Don't want them dripping on the ground... like that is some big contributor compared to the grease monster construction equipment dripping about. But I guess every little bit...