I know that with the KLX300, the stock crankcase vent hose is restricted, so out of the box you can gain a ponie or two by just replacing the hosing with some 1/2" dia. fuel line, popping a little bitty UNI filter on the end of that, and then routing it into the airbox to keep it dry.

http://www.planetklx.com/techtips/free-mods.shtml

Does the same hold true for the KLX250? I noticed that the vent hose itself doesn't really seem restricted at all (I managed to run a piece of wire clean through it without running into any sort of restrictor plug), but I did notice that the airbox outlet where it goes to seems to have an itty bitty hole about the size of a pinprick (could barely fit a piece of 24 awg wire through it).

So, if I do this, will it make any difference?

I'll probably do it anyway, just for the hell of it (since the whole shebang is so damn cheap to do), but I figure I may as well ask .

 

One of the free mods is to enlarge that hole on the airbox by drilling it out.

Others have added a small filter and routed it to up under the seat.

I used a small K&N crankcase breather filter (P/N 62-1020)and 19/32" I.D. hose (Goodyear 65187 19/32" PCV hose - Autozone stocks this).

Unfortunately, there's not enough room under the seat for this filter with the airbox lid on, so I cut out a bigger hole where the snorkle used to be. (and capped the hole on the airbox where the vent line used to go). Kind of sloppy but it works. Yes, there is a slight increase in power because there is less resistance when the piston decends.

Another associated mod is installing an inline PCV valve -- I'm not convinced that this improves anything.

 

I tried hand-drilling the airbox tonight........then tool the propane torch, heated my cheap-o drillbit and melted the hole through. Havent ridden it yet, but seems to run a little more free than it did.

 

yep, that's how you do it. heat up the drill bit red hot, lock it into the vise-grip tool and slowly push it through. much faster and cleaner than drilling.

sinko- no one I do not think said that this mod would add horsepower. I just think the claim is that it will help the engine rev quicker as it releases the compression or something on the piston letting it rev faster (not sure, I'm not an engine mechanic). don't worry about rerouting it and putting on a nifty little filter, just enlarge the airbox hole. why reroute it to the top when it's already routed to the airbox?

 

Here's why one might want to re-route it to its own filter:

The crankcase breathes dirty, oil saturated air out of its breather port. The crankcase breather port on the airbox is on the clean side of the filter. Therefore the clean intake air can get contaminated.

What's more is that after opening up the crankcase breather hole on the airbox, there isa less restrictive path for the oil from the crankcase to the get into the carb in the event you dump the bike.

 

I suppose logically that makes sense. But the chances of oil running into the airbox are pretty slim. It'd have to be darn near vertical or on its side for a long period of time. As far as the dirty air, isn't that what the filter is for? Keep it lubed up and cleaned and I'll take my chances any day.

 

He means that the vent vents right into the carb boot, on the side of the airfilter that the air flows through AFTER it's been filtered.

 

LOL, I know what he means. I did the mod nearly 2 years ago with ablow torch. Do you know what I mean? The dirty air from the cc is vented right in under the air filter. It just gets filtered like the outside air coming into the airbox on top of the filter. Just because it comes from the cc doesn't mean the air filter won't clean it. I would think it would be cleaner than the outside air since it's coming from inside the engine. It may be oily/greasy but at least it's not dirt/dust. Routing that with added parts to the top with it's own filter is a little overkill in my book and justserves the same function as the the oem setup. Really, why even have a small filteron the end of the added tubingif the hose is just on its own to begin with, what's the filter filtering the air from, the outside?
Some of the mods people do to this bike.............?????

 

Your incorrect IG, the crankcase breather enters the airbox inside of the main engine air filter so it wont get filtered. They would not put that just open to atmosphere like that, think of CC breathers on cars and trucks, there is always a filter, as with the klx, it enters after the air has been filtered, so anything coming out of the breather gets sucked right into the motor... i think over winter i am going to rerought mine and take the PCV valve out.

 

nah, I don't think so. I remember when I modded mine- I could reach my hand down there and take out the hot melted plastic leftovers. I wouldn't of been able to do this if it hadn't come out under where the air filter mounts. plus, what's this "engine side" of the airbox? it's not split, you're either on the backside of the filter or on your way through the filter. there's only one opening leading into the engine and that opening is covered by the air filter; the cc vent doesn't magically appear in the air filter mount.[&:]