KX100 & JMS powervalve by Eric Gorr

Hello all, just got me a 05 KX100 and I want monster low-end torque (I know, 2-stroke and low-end are mutually exclusive), so I called Eric Gorr thinking I would get the "we'll mill the bottom of the jug to lower the ports" that I read about so much, but instead he said that the hot ticket was a JMS aftermarket KIPS valve, saying it closes the exhaust port more, giving much more bottom-end. $150.00 and I send him my cylinder was the price. I did some research on the web and could not find one reference to this mod. Anybody heard of it? Is it the holy grail of 2-stroke bottom end?

I e-mailed the guy at JMS and he told me the PV is $169.xx for the part alone. It supposedly needs to be hand-fitted to the cylinder at an additional cost. Seems like you could just get the cylinder ported for that cost...:thumbsup:

BTW, at least as of a few weeks ago, JMS didn't have the PV on their website.

Yeah, I called him, and he told me the same thing, but Gorr told me $125 + $25 labor (give or take, I rounded it off in my head).

Eric Gorr knows fully well what he's talking about. If he says that's the hot ticket, you can trust that it is.

Yes his setup is very good for the 100's. Great setup for the woods guys. I prefer the +2mm stroker kit. Less machinework.

As for the PV, I ran a Pro Circuit with the matching governor spring.. World of difference. The stock piece is a cast steel POS. The aftermarket, JMS, PC, is chromoly steel. Much lighter and 10x stronger. After my son broke the 2nd stock PV, I figured it was time for something stronger. If I would have did it the first time, it would have paid for itself the 2nd time around.

But as far as milling the jug to lower the ports, yea it works great, but in the same concept, a stroker does something similar. Then you just have to have the head machined. Here, your best bet is to invest in a Phathead. they can machine the domes for you. Otherwise, if you choose to retain the stock head, give Bob a call at bobscycleslem.com. Mine was the first 100 head he did and I gave him all the measurements i wanted and he stuck with that.

Based on using a Wiseco prolite piston, stock bore, 06+ head, +2mm crank. It will yield you 1.25:1 more compression than stock. It was 10.05 lowside / 11.75 highside. And this ran great on pump 93.

But as far as milling the jug to lower the ports, yea it works great, but in the same concept, a stroker does something similar. Then you just have to have the head machined.

Would using the stroker crank and machining the bottom of the cylinder be a bad idea (or, just not work at all because too much needs be machined off the head)? The goal would be to increase the low/midrange power as much as possible.

yes, bad idea. It would then drop the ports way too low. you can machine the head as far as you need...to a point. But the ports are the critical point. There's a few on here that did a 103. They all loved it...or should I say their kids loved it. But there's even some adults (little guys) that still ride 100's. they did strokers as well and love them.

To put is this way, when I did my sons, way back when, he ran a kid that had a CRF150rb big bored to 174, P&P head, ferrea valves, etc etc. My son could pull on every straight away and out of every turn. The other kid was a better rider too. then we went out fun riding at an offroad park. My son drag raced my friend on his 08 KTM 250 SX-F and beat him every time..

But this was a 100lbs kid on a well built 103.

My son drag raced my friend on his 08 KTM 250 SX-F and beat him every time..


Well I called James at JMS and ordered up one of those powervalves. I was surprised to see it is made of aluminum, I am pretty sure he told me it was chromoly. It replaces the 2-piece steel powervalve with this one piece aluminum slug. It also slides in the aluminum cylinder slot. Seems this aluminum on aluminum is not a great idea for wear. I am also concerned about the powervalve expanding a lot more causing it to seize. Anyway I did install it, had to file a little on the exhaust bridge. I didn't think to take pics, sorry. I can see that it closes up the exhaust port much more than the original. Well, I fired her up and putted around, and I immediately noticed a HUGE increase in bottom end torque. I have an autoclutch and now the clutch RPMs go much higher when stalled due to more torque. I took it easy for 15 minutes or so enjoying the awesome bottom end response, I could just putt up this little 100 ft rocky hill now, where I used to have to keep my speed up.


I then decided to open her up, much to my disappointment, the top-end is way flat now, lost over-rev big time, would be much slower in a drag race. I made sure the PV was opening up by watching it with the KIPS cover off. I was hoping for more bottom with no top loss. I can see that when opened it is not nearly as aerodynamic as the original PV. Big ole 90 degree block in the way. This would be an awesome mod for a novice rider, super smooth and almost no hit. I think I still like the change for a trail bike, sure thought I could have my cake and eat it too.... hmmm, I might have to design my own PV!


I just found out that the valve is opening too late. I started power shifting using the clutch and all of a sudden she ran like a scalded dog. Seems that I needed the flare in RPM to get her to open up the PV, just won't do it under load. I think the PV gives so much bottom end that the top end of closed PV is not strong enough to rev to the PV switchover point, (or it could be sticking a little). I think I need a weaker spring so she comes in a lower RPM. I see that the Procircuit PV spring does just that. I think I will

try one. I can have my cake and eat it too....:):)

Edited by TurboStew

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