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 doesnīt have enough intake advance and has too much exhaust advance . Iīve got a service manual and when I looked at the camshaft timings Iīve 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 ainīt 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 , itīs too much , it will make the angles 89 degrees , the engine will be like a tractor : bad *** 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 itīs 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 :







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 donīt want to break or chip lobes now do whe ? A friendly word of advice : Donīt 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 Iīm 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 , wasnīt 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 :





Loock relly well at the pictures :
1) If you canīt 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 youīre 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 , Iīve 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 , itīs 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 !
Owners of carburates bikes may / will need rejetting the carb .
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 .



2) The same but with power and speed .



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



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



Ladies and gentlemen ( and those who arenīt sure ) : WE HAVE 25 HORSIES ! .
And a big fat and flat layer of torque to go with it

Edit : Due to the shape and especially the size of the intake duct this mod will yeld the best results on a KLX250 , only moderate results on a KLX300 and it provides little to no benefit on a 330 or a 350 . The 330 and 350 allready makes more lows and mids so the cam mod is also pointless on these displacements .
07-21-2011 Update
The measured piston to valve clearance is 3,2 mm for the intake valves and 2.6 mm for the exhaust valves with the mod . Without the mod is 3.4 and 2.8 mm . More than enough .

 

I run without the lid and snorkel. It's seat of the pants dyno for me, but I always knew the bike went better without the lid. Interesting that it makes about 1.5 HP more between 4.5K and 5.75K.

Good job with the cams too. I'll have to look into my AUS spec KLX250R as it's well know we get somewhat of a 'frankenbike' complete with KLX300R parts to boot. (no pun intended.) I see from the rads in your pic, the bike you have is an late model KLX250S. Interested to see if these mods go for the 07 and earlier bikes, and those 'special' models reserved for Australasia.

 

Awesome write up, I need to spend more time. Could you or some one show me how to convert to horse power or watts?

David

 

Australia and Europe bikes are almost identical , cam timings on the KLX are the same sience the 90īes , on the older or carburated bikes one will have to do a rejetting as well ( you need rejetting for just abbout every change ).
Apart from gaining 4-5 horses , the fat and flat torque makes the bike joy to ride . Iīll put later some graphs with the stock KLX , WR and CRF 250 so the difference will be clearer .

 

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







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 .

 

Really interesting, i would do it but the acr has me a little hesitant. Tremor has aftermarket cams and doesnt run the acr at all. Im thinking to make the timing adjustments and just have the acr removed. mmm....

 

I didn't read the whole thread because I am a lazy a$$.. but you get 1.5 extra hp from not having the lid on the airbox?

I have my snorkel removed, but with the whole lid of it decel pops like a mother effer.

 

Did I read this correctly or does this camshaft mod along with the air filter lid removed boost your horsepower all the way up to ~25HP?

 

Excellent write up. I was wondering why I felt such a difference when I cut out my air box screen. I thought it was just my imagination. Thanks for posting this.

 

@ EMS 0525 :Removig the ACR may be all fine and dandy but there are quite a few peple who have a bone to pick with the idler gear on the kick start . I donīt have one , mine itīs only electric start but if I would , I would have put a needle bearing in the sucker and be done with it .
Iīve had 250īs and 350īs before , one with no decompresor ( compresion ratio = 11 ) , the other ( C.R. 9 ) with a broken manual one and never had a problemm with starting , idlers etc.
@ Matasickle & jhoffy22 :Thatīs right , you go fromm 19,6 stock to 24.5 with the lid or 25.5 without it .