I'm re-routing the crankcase vent out of the airbox as described by DirtSurfer about halfway down this post https://www.kawasakiforums.com/forum...ead.php?t=8886. Using a 5/8" hose with crankcase filter on the end located up high under the seat somewhere.

I plan on using this K&N crankcase filter: http://www.knfilters.com/search/prod...x?Prod=62-1560. It has a 3/4" ID on the intake flange, which I think is larger than what I've seen used before. Along with the 5/8" hose from the crankcase, this thing is gonna BREATHE.

So my question is can it breathe too much? Should I be considering some kind of restriction, such as a smaller adapter fitting, somewhere along the way? I also know if it dumps over, the larger hose and filter could allow more oil to escape compared to stock conditions, which may be another reason to narrow things down somewhere along the way.

Thanks,
IDRIDR

 

Here's the funny thing about crankcase vents. The vent, overall, only lets out a smallish amount of blowby gasses. That's right, out. There's no need to filter this air and many OEM applications (ie the XR400) just dump these gasses to atmosphere up under the seat somewhere.

As such, you can't have a filter that's too big.

 

I have seen that many people do this breather mod. Does it make any noticable difference? Other than a larger piston/carb change I feel like I've done everything that I can to gain hp. Has anyone done the breather mod and had a seat of the pants dyno improvement?

 

I think the reason for the mod is to minimize crankcase pressure. The factory chose to use that nice big CCV tube and then put a tiny orifice in it before feeding the vapors to the clean side of the air filter. The orifice might be too tiny.

I believe that if it weren't for the emissions requirements that the CCV tube would be open ended up under the seat allowing the vapors to escape freely.

 

Highbeam - thanks for your input!

Jim - I don't know if anyone's really claimed a noticeable power increase. I was surprised at the amount of apparent blowby when taking off my oil fill plug when running, but I'm guessing that only some of that was actual blowby and most of it was oscillating pressures (in/out from piston motion).

And if I recall correctly, some just drill out the orifice in the airbox to allow more flow. The downside to that is if the bike is turned upside down, which apparently happens to some folks , the crankcase oil has a free run down the tube into the fresh air side of the air box and then into the carb. So the re-route hopefully lessens the chances of oil in the carb during yardsales, and a filter on the end should lessen the chances of crap getting back down the tube into the crankcase (my wife's grandma once said somewhat innocently "boys just like to stick things in holes"), and could reduce the amount of oil loss during said yardsale.