My bike has been on its side plenty of times ad I've yet to see any oil come out of the airbox overflow!

 

I've got a stupid question. What does the breather mod do for the bike anyways? I've read about the mod and wanted to do it to my bike, but I cant find any place that explains what is being accomplished. And an off topic question, I got a klx 300 header off of glebay for 40$ US shipped. Is it going to make any difference in performance that I will feel? Read my sig line for current mods

 

Absolutely NOT a stupid question.

The performance gains of this mod are ZERO, nada, zilche.....it is the only mod I did to my klx that showed no gain. Total waste of time and wish I never did it.

But shoot that was back in early 06 ..... what did I know


Edit: Regarding your header question.....it will make no difference in performance (same inside diameter as stock 250) but if you use it you can use a slip on klx300 muffler.....which will really help performance with proper jetting, and those slip on's can be found easily cheap used.

 

Same here. Don't think it made any difference.

But, WTF is it for then?
I'm assuming it's an enviromental thing but if the gain is less pollution, what's the loss if its not power?

It's "supposed" to reduce crank case pressure on the down stroke and allow air more air in on the up. So it's spins up quicker.
But is that just a crock? I don't know.

 

Supposed to give a little more RPM in the upper end of the range. This mod comes from the KLX300 guys, as most do actually. Does it help? Probably. Will you actually notice it? Probably not.

 

When riding right side up the vapor and oil droplets get sucked into the intake and are burned.

I hadn't even considered oil draining into the air box with the bike on its side.

Ron

 

There's really no net gain or loss. Here's why.

If the engine were turning over very slowly (maybe by hand?) it might be possible for the entire volume of the cylinder displacement to be exhausted through the crankcase vent.

But when the engine is running at speed, there is not enough time for the crankcase pressure to equalize through the crankcase vent (even an enlarged one) during a down stroke or upstroke. The result is that a pressure equilibrium is reached. The energy used to compress the volume in the crankcase on the down stroke is given back on the up stroke. Hence there is no power gain or loss.

Ron

 

Then why is it so?
Why are they just small to start with?
Why a big vent?
Why vent at all?
Why not have it the size of a pin?

Gotta be more to it.

 

Gotta let the crankcase breathe a little mate.

Your piston rings do not make a 100% perfect seal, so every time your cylinder detonates a little blows by the rings into the crankcase......gotta let it out or the pressure would slowly build up and eventually come out somewhere....could make your kick starter pop off

 

Yeh I understand that.
What I don't understand 100% is why make it bigger than it needs to be to relieve this pressure?
Kawasaki initially made the aperture big and then, presumably to reduce emissions, put in a restrictor.
If there is no consequence to the reduced vent diameter, why was it ever big?
If it does help, how and by how much?

Somebody needs to call the Myth busters .