This past week I found a local guy who was getting rid of a few parts for a KLX300. I picked up a White Brothers Mikuni 33 pumper carb, hot start, and Pro Circuit Type 496 muffler system.
I own a 1999 KLX300 dualsport that was previously all stock except for being rejetted with the 50-state needle, the breather mod, and the endplate of the exhaust removed.
I installed the muffler system first just to see of it made a difference with the stock carb and I had a free few minutes. Bolting on the pipe is a snap, it only utilizes one mounting bolt instead of the three on the stock muffler. The Pro Circuit pipe was lighter but I didn't weigh the pipes to compare.
The bike started up first kick with the new pipe and it idled perfectly with no backfire. The first thing I noticed was that this pipe is LOUD without the quiet insert. It is easily as noisy as the stock pipe without the the endplate, perhaps a few db over. A few runs up and down the street confirmed this. With just the pipe, I didn't notice significant power gains over stock. I believe that the low end was cleaned up a little bit; it was just a nice even pull from idle instead of the jumping that I had previously experienced. In my opinion, this alone is not at all worth that the 424.95 that this pipe retails for. I paid about half that as part of the deal with the carb. If anything, the new exhaust just looks nicer than the ugly black silencer and it doesn't try and melt my fender.
Next up was to install the carb. Installation took a little while but was pretty straightforward. Pull the seat, tank, and stock carb, then get out the power tools. You do have to remove the right-side engine mount t make way for the carb, I simply added two 14mm bolts in its place. I used a little grinder to get rid of the excess metal on the frame tab that was blocking the way for the new carb. There is very little space to work with so you may want to use a dremel, it will just take a little longer. Installed the carb
with the intake side all the way up against the rubber intake boot. Make sure that the drain nipple on the airbox isn't wedged against the frame, otherwise your carb won't sit right on the airbox side.
According to White Brothers, you need to use a Motion pro cable with the new carb. I used the stock pull cable with a little bit of modification. The cable was about 2mm too short so I took the cable off the bike and ground off the adjustment nut at the top by the throttle grip. This allowed the perfect amount of space for the cable to reach. Bolt everything back up and you're ready to ride.
Before the carb and pipe, my bike would be mellow down low, and then there would be a nice sweet spot about half way through the RPM range, then it would be time to shift. With the carb and pipe the sweet spot has completely disappeared. Instead, it pulls harder down low through the mid RPMs and then, as with stock, it is time to short-shift again. The most noticable effect was that the bike revs more freely now and accelerates harder out of turns. I did a 130 mile ride this weekend and the KLX and its rider were happy the whole time. The bike starts up first kick every time, hot or cold, without the need of the hotstart.
Some say the Mikuni 33 is too small for the KLX, mine is behaving wonderfully. I talked with Jerry at FSW and he reccomended the 33, and I called White Brothers and they recommended it as well over the 36. I haven't tested or ridden a bike with the Mikuni 36 installed, but I am happy with the set up I have now. The pipe and carb won't make your bike a racebike, but it will certainly enhance the strong characteristics it has. Don't get sucked into pumping up the KLX, buying a KTM would be cheaper, I just happened across a good deal. I am going to continue testing the bike with the carb and stock muffler to see if there is a difference in power. I may end up selling the pipe, I'm undecided as of yet.
Feel free to ask questions, I'll answer as best as I can.
PS. A special thanks to Brewster and the rest of KLX old guys for putting up with the same carb questions over and over again.