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KLX 250 ( 300 ) camshaft mod by Marcelino


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We all know the KLX 250 has a lot of intake noise ( many users will not run the bike without the air filter cover ) , and also has verry little exhaust noise . It seams that it does not respond verry well to escape mods , mixture mods etc. The power and torque gains are somewhat marginal , 1-2 HP tops . The only mod that really wakes up some the KLX is the elimination of the air filter cover .

All of the above means that the KLX doesn´t have enough intake advance and has too much exhaust advance . I´ve got a service manual and when I looked at the camshaft timings I´ve seen that I was right . It has the top elevation at 110 degrees after TDC for intake and 110 before TDC for the exhaust . These angle are tipical for a Ducati , BUT the KLX cannot even dream with a engine tuned for 13000 RPM or more . We ain´t got desmodromic distribution , large vertical ports , ignition advance etc. The camshafts in the KLX should be tuned for a 8000 RPM engine , due mainy for ignition mapping , carburetor/FI diameter , ports shape and size , reliability considerations . That means we should have 100 degrees not 110 . We gain in lows and midrange and we loose in the top that we will never have ( 13000 ) . The ECU ( igniter in carb models ) downright cuts the spark at 10500 RPM .

Initially I wanted to get two camshaft sprokets and modify the screw holes on them , where they attach to the camshaft . But then one day looking at the picture of a distribution I realised I can do the mod without modifying the sprockets at all .

If we look at a KLX sproket we see that it has 34 teeth , that means one tooth corresponds to 720 degees / 34 teeth = 21.17 degres . Hmm we cannot move a tooth , it´s too much , it will make the angles 89 degrees , the engine will be like a tractor : bad ass up to 3000 and nothig but peace and tranquility after that .

I needed a half tooth , 10 and something degrees .

Well , if we look CLOSELLY at a sprocket whe see that the distance between the two holes that correspond to " for INtake " and " for EXhaust " is two and A HALF teeth .

Well the solution is at follows :

For intake we give it 2 and a half teeth more advance by puting the screws in the position that corresponds to exhaust and then we retard the camshaft 2 teeth in the chain . The difference , as far as the cam is concerned , is a 1/2 tooth ( 10-something degrees )

For the exhaust cam it´s the same , but in the opposite direction : we retard the cam by puting the screws in the intake position and then we put the sprocket 2 teeth more advanced in the chain . This cam will de 1/2 teeth retarded ( 10.5 degrees ) .

When everything is said and done it will look like this :

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Most of us know that everything good comes with strings attached :

Modifying the exhaust cam advance / retard modifyies the ACR advance/retard . In this case the ACR will release the exhaust valve it touches 10 degrees later loosing a little more compression . Instead of closing arround 50 degrees before TDC it closes arround 40 and the effects are : The cold start is ... Meh , like an old bike ; the hot start is near impossible . We learn 2 things fromm this :

1) The ACR in the KLX ( at least the new ones ) is EXACTLY AT THE LIMIT . Hey Kawasaki ! What if someone looses compression due to natural causes , old age etc ?

2) I HAVE TO REPOSITION THE ACR , it means i need a press and a custom made wodden clamp for the exhaust shaft , whe don´t want to break or chip lobes now do whe ? A friendly word of advice : Don´t do this at home ! take the camshaft to a head shop and have them do the ACR . The camshaft is hollow and the ACR can be pressed out using a rod , it needs to be turned 6-7 mm ( 1/4 inch ) at the edge counter-clock-wise as you look at the ACR .

This way it will be in the same position as it was initially . I put mine 8-9 mm more avanced , this way I´m left with a little more compression and my hot starting has improved a lot over stock position . Now y never have to crank more than a second for the bike to start . What I forgot to mention is that my ACR was rubbing , wasn´t smooth , like it was a little too tight from the factory so I gave it a little session of massage and tenderising with my friendly hammer .

Here are some fotos of the ACR with the engine at TDC :

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Loock relly well at the pictures :

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 ) . Use a verry straight , sharp edge to determine all this , I´ve used a cutter blade , it seamed perfect for the job . 1 mm IS A LOT arround these parts .

Before I forget :

The bike really goes now

Have no intake grawl , even with the filter cover removed , just regular intake noise , no grawl , it´s imperceivable while the bike is moving .

My bike has the factory air filter , factory escape with catalitic converter , O2 sensor and all the other emission parts conected . I HATE POLLUTION !

For the best experience owners of carburated bikes may/will need to rejet a little . Mine is EFI so I didn´t .

Here are my dyno runs from yesterday with the cam mods :

1) Power and torque graph ( in Kgf·m ) . Red and blue with the air filter cover and snorkel on , green and yellow without .

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2) The same but with power and speed .

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3) Two power graphs , one with cover and snorkel and one without .

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4) Two torque graphs ( in N·m ) , also with and without air filter cover.

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Ladies and gentlemen ( and those who aren´t sure ) : WE HAVE 25 HORSIES ! . 👍:ride::ride::banana::D:D:D

And a big , fat and flat layer of torque to go with it :D :D :D

Edited by Marcelino
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These are the power and torque graphs for the STOCK KLX 250 , CRF 250 and WR 250 :

dynoklx250stock.jpg

crfwr250power.jpg

crfwr250torquet.jpg

Translating a bit from spanish to english :

CB or CV means caballo / cavallo = horse or horse power / HP

Torque equivalence goes like this :

10 ft / lbs = 1,38 Kgf·m = 13,5 Nm

15 ft / lbs = 2,07 Kgf·m = 20,Nm

13,86 ft/lbs = 1,91 Kgf·m = 18,8 Nm

15,91 ft/lbs = 2,2 Kgf·m =21,5 Nm

If one needs to go in the dirt like a CRF or a WR it will need a final ratio like these two have : 13 X 48 or 13 X 52 , not the 14 X 42 for asfalt duty like the KLX has .

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Ok I'm no engine guru so bare with me here. It looks like you switched which holes you use when bolting the cam gears to the cams? This changes the cam timing favorably and adds power? Also, ACR is auto compression release?

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I really don't think you'ld suffer any ill effects from just removing the ACR completely.

I did it on my XR650L when it failed and the bike ran fine after that. There was a noticeable strain starting but the bike usually fired on the first crank so it wasn't an issue. If you had to crank it for many rotations, the starter would probably overheat quickly. On the plus side, it sounded awesome. Straining against the compression then exploding with life. 👍

Nice write up.

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I generally like the sounds my bike makes as well (I also have the Q4) but noise be damned, it seems like this is a almost free ($ for gaskets and possibly modifying the ACR) mod that can gain you what, 5 or 6 horsepower at the wheel? You would usually have to get a big bore kit to be dyno'ing 25 horsepower. Makes you wonder what this mod plus a BB kit would do. Hey Marcelino how did this mod affect your gas milage?

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Never2old2learn : The intake noise denotes a restricted intake due to cam timing . I didn´t like the "intake" noise my granpa was making after 50 years of smocking . It did match his coughing ..

PTECH : It did´t affect the gas mileage at all , it´s neither better or worst , it´s because you tend to use a higher gear more and you don´t need to twist the accelerator as much . You only need a valve cover gasket if your old one is mesed up ( old , torn etc. )

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This sounds a great mod. The cam bolts and removal I can handle, but I'm not sure I understand the details of the ACR mod, either to do it myself or enough that I could convey it to a mechanic to get the result I need.

Perhaps with a bit of spelling and grammar cleanup it will make more sense 👍

Edited by Yamezz
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Before doing the cams take a good look at the position of the ACR ( take a photo ) in it´s original poistion . After you do the mod you need to put the ACR exactly the way it was .

Hope that was clear enough and free of grammar mistakes for you .

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Before doing the cams take a good look at the position of the ACR ( take a photo ) in it´s original poistion . After you do the mod you need to put the ACR exactly the way it was .

Hope that was clear enough and free of grammar mistakes for you .

Marcelino

I understand the ACR mod and this explanation is less clear than the original. There are a few details left out. This only confirms that you moved the ACR the correct amount and in the correct direction. It's not helpfull in marking the ACR and camshaft with original and corrected alignment locations.

1. This only applies to the "newer" version of the 250 and 300. A different amount of rotation could be done to the older version of the 250 and early 300 to postion the ACR in the "easy kick" position.

2. Take the picture before you remove the cam shaft from the head, while the flywheel is set to the TDC mark. You could put some sort of alignment mark on the ACR as a referrence.

3. When every thing is back together, the ACR should be in the same position, referrenced to the head, with the flywheel set to the TDC mark.

......................

It's time to use a little math.

You know how many degrees you will be changing the cam timing, 10.5degrees according to Marcelino's information. You will be moving the ACR that same amount in the opposite direction, on the "newer" version of the 250's. 10.5 / 360 = percentage ( % )of a full rotation that the ACR needs to be moved.

Measure the diameter of the cam near where the ACR is located. Multiply by pi to get the circumference ( C ).

% x C = measureable distance on the circumference of the cam to move ACR.

Mark a referrence spot on the ACR and the cam circumference. These two should be lined up.

Measure the distance from the above equation IN THE CORRECT DIRECTION from the stock mark on the cam and make another mark.

Separate the ACR from the cam, rotate it to align the marks and press the ACR back onto the cam.

I hope that doesn't add to the confusion.

Ride on

Brewster

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Showing my ignorance here, but what is the definition of 'newer' version? I have a 1999 250.

The "newer" version of the 250 starts in 2006, at least for the dual sport shipped to the USA. I'm not familiar enough with the Ausie versions to say for sure about them.

Ride on

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I have an older KLX 300 and I decided to give this a try. Doing a little thinking I realized this would re-time the exhaust cam to position the ACR in the easy kick position on the older KLXs. The process took exactly 30 minutes from the time I shut it off after my "before" test ride untill I put the last tool away. It will start by pushing the kick starter with my hand now. Much easier to turn over. Performance is a small improvement by the seat 'o the pants meter with no noticable loss of over-rev and what I thought was improved pull thruought the useable rev range. I will post more about performance after a few hours of tight single track and hill climbing.

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I have an older KLX 300 and I decided to give this a try. Doing a little thinking I realized this would re-time the exhaust cam to position the ACR in the easy kick position on the older KLXs. The process took exactly 30 minutes from the time I shut it off after my "before" test ride untill I put the last tool away. It will start by pushing the kick starter with my hand now. Much easier to turn over. Performance is a small improvement by the seat 'o the pants meter with no noticable loss of over-rev and what I thought was improved pull thruought the useable rev range. I will post more about performance after a few hours of tight single track and hill climbing.

If you bike is a 300 than it´s carburated , you need to redo the jetting / mixture on it because after the mod the bike rus a little leaner .

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If you bike is a 300 than it´s carburated , you need to redo the jetting / mixture on it because after the mod the bike rus a little leaner .

Actually, I think the jetting was pretty close. A little more time on it will tell, though. There was no lean hesitation, popping, or anything of thar nature. It ran smooth and steady at constant throttle, but I'll check the plug color and see if any changes are warranted.

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Would a kawasaki shop know what to do if i told them or would i need to bring in Marcelino's instructions for them to understand what i want done to the bike? I am not about to attempt this by myself. I'll re-jet along with this mod, i'm wanting a 'lil more poewr outta this thang!

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Would a kawasaki shop know what to do if i told them or would i need to bring in Marcelino's instructions for them to understand what i want done to the bike? I am not about to attempt this by myself. I'll re-jet along with this mod, i'm wanting a 'lil more poewr outta this thang!

I don´t think they will have any problem understanding the mod , I´m not sure if they will be willing to do the mod ( think there might be some legal issues with that ) ; a regular bike shop is a different story . You could always ask , it does not cost money .

I think it´s better if the mechanic can have a look for himself at the post ( you may need to be logged in to see the photos ).

Then , you can take the bike to the dealers , put it on the gas analizer and have it rejeted .

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