I was doing some pseudo-scientific research and experimentation during our ride today. My KLR650 has a lot of mods on it. I've done carb work, airbox work and other tinkering with the engine. It runs quite well for what it is.

Myself and another "tinkerer" got playing with something last week and I'm so impressed with the results that I might just give it a try on the KLX250.

Both of us are ex-drag racers and have built some great motors in our careers there. One of the things we had done was play with some crankcase evacuation pumps to get the pressure reduced inside the engine. We tried a stupid little idea and it is looking like it is doing what we thought it might do.

I installed a PCV on the crankcase of my KLR650. There is a tube that runs from the crankcase to the airbox - very similar to that on the KLX250S. Now, our thoughts are this; when the piston is on the down stroke, air is forced out of the crankcase, on the up stroke, air is sucked back in. That is what the PCV is going to correct. Now on the down stroke, air is forced out of the crankcase, but on the up stroke, the PCV prevents the air from being sucked back in. Our thoughts are that this air being pushed out of the crankcase is why there is a bit of a gain by enlarging the opening in the tube from the crankcase to the airbox on the KLX250. Bigger hole lets the air move quicker. Now, it we don't let all that air back into the crankcase, we don't have to worry about moving it all back out.

So this morning was my test ride of this theory. I noticed some interesting observations during my test ride today:

o The rider must be careful of the rpm's of the engine. With the PCV in place the engine revs almost too easily. I saw deep into the red zone this morning - before I knew it. The engine just revs so quick now.

o The bike seems to like 5th gear (top gear on a KLR650) from 2200 rpm up to the redline!

o The bike seems quite smooth!

o If the rider is not careful, upon shifting into 2nd gear with the engine at redline, the front tire pops up! [sm=icon_rock.gif]

Now, the BMW F650GS Dakar has about 12 more horsepower than the KLR650 and I have about 100 pounds on Mike, but the KLR stayed with the BMW on our single acceleration test! I was impressed with the way the bike ran.

Does this mean the KLX250S will respond as positively to Postive Crankcase Ventilation? I don't know until I try it. I found a "standard" PCV for $2.98 at Advance Auto Parts - PV895. I'm going to stop and get another one tomorrow, install it, test it, then takes pictures and post a report. Stay tuned!

 

sounds good.it will be interesting to hear what you find out.i'll be checking back.

 

Dollar for dollar, this could be the best and easiest mod yet! [sm=interesting.gif]

However, I'm not sure I fully understand how it works. If air is not able to reenter the crankcase after being pushed out on the down stroke, doesn't the up stroke create a vacuum situation which would impede the up stroke and tend to negate the positive effect of it helping on the down stroke? Are there any other concerns with the greater negative pressure inside the crank case - oil seals, etc? At any rate, the proof of the pudding is in the eating. I'm very interested to hear your results.

 

Keep us posted Marty, and pics, pics, pics.

 

Well...?? I've been chomping at the bit to hear about the results of this PCV valve mod!
You mentioned the engine revs almost too quickly... I wonder if one could somehow reduce the efficiency of the PCV valve to compensate?

 

a pcv valve with a stiffer( harder) spring in it would probably work, it wouldnt let it open as easy.

 

Kawi Wawi,

First off, please accept my apoligies. I chose to go riding this beautiful weekend instead of working on the bike. I know I'm not doing what I should be doing, but it was just too nice a weekend and Sullydirt needed a riding buddy on his trip out to Pensacola Beach this weekend.

I will now get right on it.

Sorry for the delay.

 

No worries Marty... Can't wait to hear your results.
@EMS_0525 - I was thinking a looser spring in the PCV, so that it lets air flow 100% freely in one direction and 50% freely in the other.
That would allow air to escape from the cases easily, and be drawn back in only slightly.
Or maybe a pin hole in the PCV diaphragm.

 

I was reading the owners manual last night and there's a paragraph describing the function of the smog crap (Kawasaki Clean Air System or something like that). It basically says that the little doohickey on top of the valve covers is a one-way air valve letting air only flow towards the exhaust from the airbox. So... Since we're all just removing that crap anyway, maybe it would fit onto the crankcase breather system and have the same effect as the PCV.

 

i thaught that the air was gettin out too quickly, is why it revved real fast, which is why i said a stiffer spring to not let the air out as fast.... is my thinking wrong?