Kientech Jet Kit
Or "How to Perfect Your Suzuki DR200SE."
The DR200's low-powered engine is handy enough off-road, and in town. Useable power, but it's not going to get you into trouble. On the highway, however, it can be a little bit of a drag. At highway speeds the DR has trouble coping with high winds or steep grades, and Wellington has both in spades. It's a close-run thing, though -- I had the feeling that the DR was only just struggling, right on the cusp of being able to hold its own, if it just had a tiny bit more power.
I'm no expert on carburetors, so buying a complete jetting kit -- the only complete kit -- from Jesse Kientz held some attraction. Jesse's complete modification includes modification to the stock exhaust. Obviously I wasn't going to send my muffler all the way to the States, so Jesse sent me some instructions, and the parts needed, for a few bucks. All told, I think I paid about NZ$46, and my kit arrived within the week.
I sent the instructions and parts off to a local exhaust fabricator, who did the necessary while I was on vacation. It was ready on my return, nicely finished. You'd be hard-pressed to tell the difference without a stock muffler to compare it to. Next, I cut a two inch hole in the top of the airbox lid with a hole cutter, as per instructions.
The rest of the kit comprises a larger main jet, a larger pilot jet and an extended fuel air screw to make it easier to adjust the pilot fuel air mixture. Also, some instructions that don't quite match my carb. They'd probably be sufficient if I were already an experience carb-twiddler, but as I've said already, I'm not. so I was left guessing a little bit here and there.
I took a few snaps of the carb in place before I started, just so that I had something to refer to when I was putting it all back together. Then I drained the carb bowl, pulled the side plastics, the seat and the tank -- which meant disconnecting the vac and fuel lines from the carbuetor to the fuel tap. I unmounted the three airbox screws and loosened the two clamps holding the rubber boots onto the airbox- and engine-side of the carb. I pushed the airbox back, then popped the carb out. Once out, I removed the throttle cable end from the cam and unscrewed the throttle cable from the adjuster by turning the whole carb on the end of the cable.
Three of the four zinc plated screws holding the carb bowl on came out without trouble. The fourth was seized and required drilling. I put it back together with some random spares but replaced them all later with some good quality stainless steel screws. I slipped a washer over the remains of the drilled-out screw and used a swiss file to put a couple of flat faces on in. Some mole grips bit on those good and tight and the screw finally came out. While I was at it, I removed the tickover adjusting screw and straightened it (how'd that get bent) and then cleaned the threads up before putting it back in.
With that dealt with, I replaced the main jet and pilot jet as per instructions, no troubles. Then on to the fuel air screw. This is where my carb differed slightly from that pictured in the instructions. Not aided by the fact that my fuel-air screw was hidden behind a brass blanking plate. You can see it bottom centre in this picture, marked with a blob of white paint.
I did some reading around before going any further. In the end, I drilled out the plate with a series of successively larger drills to reveal the screw behind it, which I then removed. With that done, I offered up the new screw and guessed that I'd need to remove about 8mm of the tube into which the fuel air screw was to be fitted. I marked it up and set to with an angle grinder. 8mm turned out to be a little more than necessary, but not too much.
The instructions go to some length to explain how far in the fuel air screw must go, and how important it is that the threads are clean. With good reason. It took me several attempts to get the screw fitted; clean, screw in, screw out, repeat. Jesse's suggested starting point for tuning the mixture was close enough that the bike started and ran okay. Installation was the reverse of removal, as they say.
I had to read around to get a good idea on the proper procedure for setting the mixture. Not helped by some fairly loose use of terminology. To the complete novice, it's very hard to tell who's talking out of their hat and who isn't, who can be trusted. Many sources seem to use the terms "fuel screw" and "fuel air screw" as if they're synonyms. Others state plainly that they aren't. And then there are "air screws" to add to the mix, (pun intended.) This is a fuel air screw, or maybe a pilot screw, but that's what it is, and adjusting it isn't rocket science once you've found some instructions that make sense. Sadly, I've lost all of the links that I collected while reading, which would have enabled me to confidently explain the difference between air, fuel air and fuel screws. So for now you'll just have to add me to the very, very long list of ill-informed jerks claiming to know what you don't.
You should already know how far in the screw was set to start. As you adjust it later, count the turns in and out so that you know how to reset the screw without going through this process again. Take the bike out for a ride. Get it warm. Bring it back to your well lit and well ventilated garage and leave it running. Wind the tickover adjust up. Begin unscrewing the fuel air screw, the revs should rise, plateau, then fall. Stop. Start screwing the fuel air screw back in. Listen closely to the revs as they rise, then plateau. As soon as they start to fall again, stop. Now screw the fuel air screw back out half a turn. Reset the tickover adjust. You're done.
Record the way that the flat face of the screw is facing, and the numbers of turns in your screw took to get here. Mine's at 131/8 turns. After a decent run-in has passed, you can check the colour of your spark plug to gauge whether your mixture's too lean or too rich, but a couple of people have suggested that this no longer a reliable indicator with modern unleaded gasoline.
I'm extremely pleased with the results. The bike sounds much less like a sewing machine and much more like a motorcycle. It's not too noisy, but it has a pleasant bark when the trottle is opened up. It's still not a fast or a powerful bike, but the difference is noticeable. I had been worried about increased fuel consumption, but I needn't have been. I very rarely have to shift gears now to cope with high winds or steep grades. I spend a lot less time in fourth gear. My fuel consumption has actually improved, from an average 65mpg (US) to an average 78mpg (US). By now, it's paid for itself.