I know others will disagree with me. The crankcase breather lets the air in and out of the motor thats below the piston, when the piston comes down the air just pushed out of it, when the piston goes up air gets sucked in. Might it help to make it a little bit bigger, maybe, but the pain in the *** of doing it isnt worth it in my opinion. I would challenge for anyone to be able to tell if it is done or not on a bike. I take all mods with a grain of salt... i have pretty much done everything/anything i can to my bike. Some mods help others didnt notice a difference. Too many people look at things like this is a race bike... its not. I havent enlarged the hole in my airbox for the breather. i have ridden bikes that have had it done. Save the time and just ride...

 

I don't think any mods to the crankcase venting on most motorcycles have any performance/power impact, but it clearly might have some influence on oil consumption...especially on some engine models. There's a lengthy discussion mainly contributed by a guy with the forum name "KLR Cary" over on the KLR World forum. This guy was with Schnitz Racing who developed the 685/705 KLR big bore kit, among other products for that company. His indepth descriptions on crankcase pressure as it applies to both performance and oil consumption in internal combustion engines are very enlightening. He was a pretty knowledgeable guy. Relieving crankcase pressure in certain ways and at certain times can affect performance in some engines and benefit most engines in the vein of oil consumption to some degree even if it's small. Read some of his assessment on it and make your own mind up.

I did the PCV valve/crankcase mod on a low mileage KLR650 that was prone to using oil, and it reduced oil consumption by about half over a long period of use and observation. All KLR650's don't use excessive oil, so apparently the mod isn't necessary for all of those models and is a slight bandaid for another debateable problem in that engine. Our KLX's don't seem to have any high oil consumption issues as a trend. A smaller bore and therefore less fluctuations in crankcase pressure may contribute to that. We do have somewhat higher rpm, but the smaller bore and other design issues probably alleviate the pressure. I didn't put a PCV valve on my KLX crankcase vent, but I did drill out the vent hole in the airbox to a larger size. I had the airbox off during some other extensive servicing when I got the bike, and I drilled the airbox conveniently at that time. I wouldn't pull the airbox to just drill the hole larger, as I don't think it's a critical necessity on our bikes. Though not necessary, and I wouldn't obsess over it, maybe you can drill the breather hole out at some point when you have easy access to the box. Otherwise I wouldn't lose much sleep over it.

 

It's purpose is to vent blow-by pressure, exhaust gasses and some air/fuel charge that leaks past the piston rings and builds up in the crankcase. Routing it to the airbox is just an EPA deal added on later.

 

Okay.. I don't think I will be doing that mod necessarily..
Any other mods that can be recommended that are on the easy DIY side?
I have my DJ kit and HMF exhaust on order..
What's next?!

 

stock gearing is 14/42, mine is at 13/45.... it is worth it. Makes woods riding better, you do loose some top end on the street.

 

I have a 2009 SF.. is the gearing different for the motard setup? (I also do 90% street..)

 

Ignore my comment. If you do that much street get a K&N air filter.

 

Good call.. will look up and get that ordered..

 

Again, I wouldn"t put a K&N air filter on. I work on bikes, the damage done by ingested dirt on this type of motor is VERY costly. A properly maintained stock/twin-air/uni foam filter is way better.

 

Okay.. scratch the K&N.. didn't know there were issues with it..