Hi people, it seems the humble KLX has a number of interested followers. The secret is out. I've found them to be light weight, handle better than most bikes of that era and if you can coax a bit more power out of them they hold their own on a motocross track.
Below for what its worth are some of the lessons I learn't and sources for parts I found when making the KLX engine go a bit harder.
As said before if your going to ride it hard get a Megacycle cam with the roller bearing mod or at least rebush the head where the cam runs using suitable bronze bushes.
If you do nothing else, get a piece of 12.5mm diameter aluminium rod 36.65mm long, take out the tacho drive in the head and put this in its place.(Comes std with a megacycle cam) You will have to cut down the spiral gear on the end of the std KLX cam that usually drives the tacho drive, but once done all the oil will now go to the rockers and cam.
With your new or reground cam only ever use new or reground rockers. While on the subject of oil, I found out the hard way that oil companies over time reformulate oil blends and while they sometimes put in better additives and also remove some of the old ones that were there to protect rocker pads rubbing directly on cam lobes. I now only use Belray Thumper oil and into 4 litres of it I pour a bottle of Comp Cams engine break in oil additive. ( it puts back all the good stuff) Its available from most performance engine shops.
Don't skimp- put in a new oil pump and very importantly put a new mesh screen that filters out any big bits (relatively speaking) before the oil goes to the pump.
Replace the head bolts with new ones. I have a number of engines and not one of them did not have stretched head bolts. The difference in length between new ones and used ones is enough to make you think you have the been supplied the wrong part. Since doing this I have no more leaking head gaskets. Torqued down to 25 psi they hold everthing together even with high compression ratio's (12:8:1 in my case)
I fitted a wiseco piston 72mm- 2 mm oversize (PT NO:4052 M07200) You may need to modify the piston top or valve cut out depending on the cam you use in order to prevent the valves hitting the piston at TDC.
If you get valves made, resist the temptation to have them made over size. Even 0.5mm oversize causes a problem with high lift cams as the valves run into each other on overlap at TDC.
Valves I got from RD Springs in the good old USA. I also get Valves springs from them. PT NO: VSK301-K. They don't have them stock but wil make them for you. If you can find some, S&W made them also PT No: 11-026A
All ths new power and youmight want H/duty clutch springs- try Vesrah PT NO SK-406
Funny thing about engines, if you change one thing you gotta change the rest if you want it to work right. An engine is an air pump. Once I bored it out and put a better cam in it, next came a bigger diameter exhaust and rejetted carb. It still would not run properly on the mainjet regardless of the jet size. Problem was not enough air. The only way I could fix that was to take that immaculate hard to get air box and drill the sides of it full of 1/2" holes
I set the ignition pick up on the flywheel with exactly 1mm clearance, never touch the throttle and it starts if its hot or cold. Spark plug standard is a heat range of 7. I use 8 and in some cases 9 (Long periods at full throttle)
Last thing I can remember is to check the cam chain tension bolt. The bolt is only meant to hold the tensioner mechanisim back when its fully retracted (for assembly purposes) The rest of the time it bottoms out and does not touch the rod inside the tensioner. The tensioner now self adjusts to keep the correct cam chain tension. Over time, often well intentioned people have replaced the bolt with a longer one. This locks up the tensioner and prevents it from self adjusting and leads to major damage due a slack cam chain.
Thats me done, I hope this is of some use to others, saves you some time and money and gets a few more KLX's on the track.
