KLX 250 ( 300 ) camshaft mod by Marcelino
Senior Member
1st Gear Member
Joined: Oct 2010
Posts: 277
From: PNW
I took my bike apart today to do this mod. Took the cam to a local shop and they moved the ACR for me for $20. Looking at the ACR (from the left side of the bike), they moved it 1/4" counter clockwise, per what I read in the first post.
So I came home and moved the sprockets, and reassembled. This is what it looked like:
You can (barely) see the marks I scratched onto the sprockets, pointing towards one another.
After putting the holder back on and redoing the tensioner, I rotated the motor a few times, then went back to TDC. This is what I saw:
The marks I inscribed are now pointing outwards, and the cam lobes are NOT pointing outwards. Yet the sideways "T" is in the little window. So... I'm wondering if I've done TDC right. Figured I'd ask before trying to start it.
I see on the flywheel, the sideways T, and right after it, an F. But I think when I set TDC the first time, there was just a sideways T and no F following it. If I spin it around to the sideways T with the F just past it, the marks line up and the cam lobes are pointing outward like they're supposed to.
So... did I do it wrong?
Rob
So I came home and moved the sprockets, and reassembled. This is what it looked like:
You can (barely) see the marks I scratched onto the sprockets, pointing towards one another.
After putting the holder back on and redoing the tensioner, I rotated the motor a few times, then went back to TDC. This is what I saw:
The marks I inscribed are now pointing outwards, and the cam lobes are NOT pointing outwards. Yet the sideways "T" is in the little window. So... I'm wondering if I've done TDC right. Figured I'd ask before trying to start it.
I see on the flywheel, the sideways T, and right after it, an F. But I think when I set TDC the first time, there was just a sideways T and no F following it. If I spin it around to the sideways T with the F just past it, the marks line up and the cam lobes are pointing outward like they're supposed to.
So... did I do it wrong?
Rob
Senior Member
1st Gear Member
Joined: Oct 2010
Posts: 277
From: PNW
Rob
Senior Member
1st Gear Member
Joined: Oct 2010
Posts: 277
From: PNW
Okay, so I went ahead and put it back together. It fires up and runs, sounds fine. So I put the tank and plastics back on and went for a ride with my wideband O2 sensor attached. I noticed it was going lean in the midrange, which I had pretty much expected to happen. It was just about perfect before.
So I came back and did a quick carb change. I moved the clip down to the bottom-most groove. It had been on the fourth groove with a shim under it. Went back out. It was back to how it was before... just about ideal. BUT... my odd "miss/surge" at 7000 RPM was back that had been cured the other day by grounding the regulator to the motor.
As the ride continued around my usual test loop, the bike started running worse and worse. It was missing pretty bad, and sputtering down below. The O2 sensor showed it a bit fat at light throttle, which it had been showing since the first test ride. But that just didn't seem like it. I stopped and made sure the spark plug boot was on good (it was). Then I played with the AF screw. I could turn the screw all the way in and it'd still idle (barely). It got a little better as I turned it out, around one turn total. And this is with the stock 35 pilot jet.
So to recap my jetting -- I have a 135 main jet (equivalent of a DJ126), the DJ needle on the bottom-most groove, and the 35 pilot jet. Mods are KLX300 pipe and exhaust, Twin Air filter, KDX snorkel, and the 351 kit. I knew I probably wouldn't see a lot of gain from this mod since I had the 351, but I mainly wanted to quiet down the intake noise.
Any ideas? Any possibility I might have gotten the timing off by a tooth? The motor sounds just fine. No odd clankings or other noises. It felt stronger in the midrange before it started running like crap.
Rob
So I came back and did a quick carb change. I moved the clip down to the bottom-most groove. It had been on the fourth groove with a shim under it. Went back out. It was back to how it was before... just about ideal. BUT... my odd "miss/surge" at 7000 RPM was back that had been cured the other day by grounding the regulator to the motor.
As the ride continued around my usual test loop, the bike started running worse and worse. It was missing pretty bad, and sputtering down below. The O2 sensor showed it a bit fat at light throttle, which it had been showing since the first test ride. But that just didn't seem like it. I stopped and made sure the spark plug boot was on good (it was). Then I played with the AF screw. I could turn the screw all the way in and it'd still idle (barely). It got a little better as I turned it out, around one turn total. And this is with the stock 35 pilot jet.
So to recap my jetting -- I have a 135 main jet (equivalent of a DJ126), the DJ needle on the bottom-most groove, and the 35 pilot jet. Mods are KLX300 pipe and exhaust, Twin Air filter, KDX snorkel, and the 351 kit. I knew I probably wouldn't see a lot of gain from this mod since I had the 351, but I mainly wanted to quiet down the intake noise.
Any ideas? Any possibility I might have gotten the timing off by a tooth? The motor sounds just fine. No odd clankings or other noises. It felt stronger in the midrange before it started running like crap.
Rob
Senior Member
Joined: Feb 2011
Posts: 628
From: Northern Kettle Moraine
1st Gear Member
You should have read the whole cam mod thread. The cam mod does not work with the big bore. You can just retime the intake cam and should be ok. I had the cam mod with stock bore, when i went BB I retimed intake and left the exhaust as I did not feel like dicking with the ACR at the time. It runs great and one day I will retime the ACR and put the ex. Cam to stock. Sorry to be the bearer of bad news. Edit..you may try a larger main before throwing in the towel. I have a similar setup and it really likes the DJ132. I tried alot of combos and it seems to like running a bit rich. Best of luck.
Last edited by 2veedubs; Jun 22, 2013 at 02:48 AM.
Senior Member
Joined: Jun 2013
Posts: 3,315
From: North Texas
1st Gear Member
Did Marcelino's cam mod today... New 2012 KLX250S with 320 miles on odometer. Only mod is a DG slip-on. 101% stock otherwise.
750ft ASL , 101F , Dallas Tx.
The instructions on how much to reposition the ACR is absolutely correct.
I gave my ACR a few more millimeters as Marcelino did just for good measure. Bike starts hot with one or less revolution - it's instantaneous, far better than before the cam mod. If you have to ask how I performed the ACR removal and reposition you probably are not equipped to do the task yourself.... I created a somewhat crude collar for the cam in my garage machine shop and drifted the ACR out with a big hammer.
Bike runs stronger. Very noticeable increase in power even with stock induction. Stock carburation calibrations are sufficient as there are no flat spots during acceleration.
Tomorrow I am installing a Stage 2 Dynojet kit as per its' instructions.
I hope the stage 2 will allow me to run with the airbox lid off as well.
750ft ASL , 101F , Dallas Tx.
The instructions on how much to reposition the ACR is absolutely correct.
I gave my ACR a few more millimeters as Marcelino did just for good measure. Bike starts hot with one or less revolution - it's instantaneous, far better than before the cam mod. If you have to ask how I performed the ACR removal and reposition you probably are not equipped to do the task yourself.... I created a somewhat crude collar for the cam in my garage machine shop and drifted the ACR out with a big hammer.
Bike runs stronger. Very noticeable increase in power even with stock induction. Stock carburation calibrations are sufficient as there are no flat spots during acceleration.
Tomorrow I am installing a Stage 2 Dynojet kit as per its' instructions.
I hope the stage 2 will allow me to run with the airbox lid off as well.
Senior Member
Joined: Jun 2013
Posts: 3,315
From: North Texas
1st Gear Member
Did the cam mod yesterday - see my post above...
Elevation approx. 750ft ASL ..... Air temp 100F
Today I installed the DynoJet kit using stage 2 components exactly as per the instructions. Removed airbox lid.
The bike starts instantly and runs flawlessly throughout its' RPM range. Stage 2 without airbox lid works perfectly.
Power increase is incredible. The bike will pull clutch unassisted acceleration wheelies in first gear.
Want proof ? HERE IT IS - http://www.youtube.com/watch?v=iJEF5...ature=youtu.be
2012 KLX250S , new with 320 miles on odo , cams re-time mod with ACR reposition , DG slip-on , Dynojet stage 2 , airbox lid removed
Elevation approx. 750ft ASL ..... Air temp 100F
Today I installed the DynoJet kit using stage 2 components exactly as per the instructions. Removed airbox lid.
The bike starts instantly and runs flawlessly throughout its' RPM range. Stage 2 without airbox lid works perfectly.
Power increase is incredible. The bike will pull clutch unassisted acceleration wheelies in first gear.
Want proof ? HERE IT IS - http://www.youtube.com/watch?v=iJEF5...ature=youtu.be
2012 KLX250S , new with 320 miles on odo , cams re-time mod with ACR reposition , DG slip-on , Dynojet stage 2 , airbox lid removed
Last edited by Klxster; Jul 13, 2013 at 07:17 PM.
Senior Member
1st Gear Member
Joined: Mar 2013
Posts: 866
From: SE Asia
I would probably go for this cam mod instead of going thru the international shipping of a big bore. But I don't understand the OP's instructions about how to determine the new positioning of the ACR..
The round end of the ACR appears to be neither level with the head nor with the box cutter blade. Which appears to conflict with his instructions:
"1) If you can´t see ALL the round piece above the edge of the head your ACR is too advanced , it leaves too much compression and you may damage the starter and/or the starter torque limiter ( the piece that the starter engages )
2) If you can see 4 mm or more of the piece below the round one the ACR is too retarded , you loose to much compression and will not start .
I think if you can see the round piece and only the half moon fromm the piece fromm below you´re allright . If you want a little more compression ( like me ) you can leave it so that only the round part is visible ( all of it , and the very tip of the half moon ) ."
Can someone clear this up for me?
The round end of the ACR appears to be neither level with the head nor with the box cutter blade. Which appears to conflict with his instructions:
"1) If you can´t see ALL the round piece above the edge of the head your ACR is too advanced , it leaves too much compression and you may damage the starter and/or the starter torque limiter ( the piece that the starter engages )
2) If you can see 4 mm or more of the piece below the round one the ACR is too retarded , you loose to much compression and will not start .
I think if you can see the round piece and only the half moon fromm the piece fromm below you´re allright . If you want a little more compression ( like me ) you can leave it so that only the round part is visible ( all of it , and the very tip of the half moon ) ."
Can someone clear this up for me?
