As a result of sitting around up in Tellico Plains, Tennessee one evening around the campfire, drinking a couple of "adult beverages", telling war stories and discussing bikes, I got an idea. One of my friends was there and we got off talking about engine mods. Back when I was drag racing, we used crankcase ventilation pumps to clear the crankcase of power robbing pressure. KLRCARY, who is a top wrench for Schnitz Racing told me about just the thing he was playing with on his bike. "It will give you about the same results as you're currently getting from removing the snorkle, shimming the needle, drilling the slide and opening up the pilot jet." I was already planning on playing around when I got home.

Another friend called me up one night and he sounded like he just put nitrous on his bike and had sniffed a bit of it in the process. "You won't believe the difference in your bike - Ya' gots to try the PerCiVal Mod!"

The PerCiVal Mod is so named as we are installing a PCV valve from a car into the breather hose that runs from the crankcase to the air box. The idea is that when the piston comes down, it forces the air out of the crankcase and then the valve closes and keeps air from coming back in.

Well, I did the PerCiVal Mod on my KLR650 and I was very impressed. The bike had a new issue, the tach was wrapping up to 9500 rpm before I could shift! The redline on the bike is 7500! Yikes! So, I'm kind of careful when I ride it now.

One of the characteristics on the KLR now with the PerCiVal Mod installed is the front tire likes to life itself in 1st gear with a quick twist of the wrist. It has a lot snappier bottom end and great throttle response. Now, with shims, slide drilled, snorkle removed, pilot adjustment set to 2 1/8 turns and the PerCiVal Mod installed, it bike, quite frankly will run away and hide from any other KLR650 out there.

I was very happy with the results, so I decided to put the PerCiVal Mod into my KLX250S. But I accepted a new position in June and have also switched my MSF sponsor and have wound up working 7 days a week with this being the second weekend off since mid June.

Well I said I was going to do some semi-pseudo-scientific-research and tinkering when I had the time off, so here goes:

The PerCiVal Mod

To begin the mod you need to remove the hose that connects the crankcase to the airbox on the KLX250S. Once off, it will look like this:




For the PCV to work properly, it must be oriented vertically. To make a spot to put it, I sliced the hose here:




Next, I test fit everything and noticed that the top of the PCV valve needed a bit of and adaptor made.




So I hunted in the scrapbox and found a piece of gas line and cut about 1/4 inch piece and slipped it over the top end of the PCV. It fit like it was made for the job!




A couple of cable ties and the modified crankcase hose is ready to go back on the bike.




Here it is, back on the bike ready to be ridden.





How well does it work? I don't know, but that's where I going to go right now. I'll be back with more info. Stayed tuned!

 

Marty...your killing me! TEASE!!!!!!

 

Thanks Marty! Great photos and explanation. Two questions:

1) did you reconnect the free end back into the air box or did you cap off the air box and leave the free end open to the air?

2) what PCV valve did you get - do you have a part number? I know the ones for my Pathfinder don't look quite like that - it is metal and threads into the engine so it would not be condusive to fitting inline in a hose. I'm just curious as to what to ask for at the parts counter and know it will work when I get it back home.

I can't wait to hear your results.

 

OH MAN!!!! More mods? Alright Marty, if you say so.

 

Well, I just got back from riding some dirt roads.

The little bike with spin the tire THROUGH 1st and halfway through 2nd gear when you whack the throttle!

The bottom end is awesome, mid range is way cool, but I think I'm going to have to go up to a 128 main jet as I'm getting a bit of lean surge on the top end now.

On the "What PCV did I use?" question, I'm not sure. I went into the local NAPA (one of the benefits of a small town) and searched for something that would fit. No, it did not have a box, so I don't have a part number. I'll drop down and see if I can come up with a part number. However, it's not expensive, I believe less than $3 for the part, which at my local NAPA store means you can get it for about $1.50 at Autozone! [sm=boohoo.gif]

I reconnected the hose just like stock. No flying end!

I'm going to play with the jetting - not now as it's HOT ! How hot is it? Too HOT to enjoy riding! Now that's HOT!

 

Thanks Marty - sounds like the best $3 you can spend on this bike

This one is definitely on my list.

BTW, when is that Tellico rally I think you mentioned a while back? Not to get off-topic here, but maybe you could start a new thread on that. I'd like to try to make it if at all possible.

 

Hey Marty that sounds like a good mod to do If you could let us no what part number or car it fits my local auto stores SUCK they won't help with anything if you can't give them a part number or car model and year they just blow you off...... I like the old days when you had service from people not just computer button punchers

 

I started thinking about it and know that the part number is very important. Once again, thank God for living in a small town. I called my buddy and asked him about the part. We went down to his NAPA store, opened up the back door and went hunting. Matched the parts up and here's what we got:



And here what y'all are looking for . . . . .

 

HUH? I can't tell what this means from the picture, can you elaborate??

 

Thanks for going through the trouble Marty I will pick one up at Napa tomorrow.....

Again Thanks