Hi, I’m Steve Matthes, 2003 Budds Creek first moto winning mechanic and I’m also Transworld Motocross editor at large. Carburetor’s on four strokes are scary things to a lot of people but I’m here to show you guys it’s not so scary. And with a little bit of knowledge and a little bit of tuning, you can have your bike running perfect. This week on the Transworld Motocross How To presented by Bike Bandit, we’re gonna talk about how to rejet a carburetor.
All right, so I’ve removed the carburetor from the motorcycle. I’ve taken the top lid off as well, taken off the opening to the needle jet. And what you can do is move the slide up, reach down in there and pull out the needle. As well, I’ve taken off the four screws on the bottom of the flow pull. Taken that off and exposed the main jet and the pilot jet. All right, so the needle affects your powerband throughout most of the range. And it’s a pretty massive change to make one clip difference. So what we’re gonna do here is I’m gonna show you how to make the bike a little richer. So if we take the needle, put it on a flat surface like your toolbox or somewhere, push down with your thumb. Now, make sure you count the number of clips slots that the clip is down. This one, in particular, is down four from the top, always count from the top. So what I wanna do is make it a little bit richer. So I’m gonna move it down to the fifth one which, in effect…push it back down, it’s on the fifth slot. What that does is raise the needle up and allow more fuel into the carburetor, thereby making your bike work a little richer.
All right, so what we’ve done is made the needle richer but you can also do the opposite, which is make it leaner. You would want to raise the clip, drop the needle, that’ll make it leaner. Make the bike have less fuel, give it a little bit of throttle response, and you’ll notice the difference of the seat of the power plants immediately upon doing that. Loosened the main jet already. Here is the main jet, this is a 175. On the main jet, the bigger number means richer. So if you want more fuel…and this jet controls three-quarters to a wide open throttle. So if you want more fuel, if you’re getting cracking, popping up top, you’d wanna go to a 178, which is the next step up, or a 180 even. The bigger number on the main jet means more fuel.
All right, well for the purposes of this video, I took the bottom flow pull off. But what you can do is simply take out this 17 drain bolt on the bottom and you can get to your main jet and your pilot jet this way, so you can tilt the carburetor on your bike. Now, most people, they talk about a leak jet and a diaphragm. I find that in today’s bikes they’re jetted pretty well. You shouldn’t need to really adjust those too much. The diaphragm you can go up in sizes and the leak jet the same thing, which controls the amount of fuel that gets onto your diaphragm. But I would recommend between a pilot and a main, and a needle, you can make any change you want. Look in your owners manual, it tells you what kind of conditions to go richer, what kind of conditions to go lower, or leaner I should say and you’ll go from there. While the carburetor’s off, while it’s on the bench, it’s a good idea to check your air screw, and you should probably put that somewhere about…count the turns. This one is one, one and a half, this one’s one and three-quarters. Probably not a bad place to start, but I like to go one and a half. There’s one, and there’s a half. And bikebandit.com will sell you a easy tool to get in there while you can do this on the bike.
All right, now what I’m doing is taking out the pilot jet. The pilot is anywhere from close throttle to a quarter throttle. If you notice your bike maybe hesitating a little bit, you probably need to go richer on the pilot jet. Same thing as the main jet, the bigger number, the more fuel.
So this is a 42 and you can see the number on the side of it. Same as the main jet. So if you’re noticing a little bit of cracking, a little bit of popping on the bottom, go to a 45. It’s pretty easy to do, pretty easy to change. So drop the 45 in there, and you’ll get more fuel in there, and that’ll solve that problem.
All right, so there you have it. I’ve covered the main jet, the pilot jet, and the needle jet, the three jets that are the most important in your carburetor. If you have a fuel injected bike, scratch everything I just said. It’ll be jetted for you perfectly all the time. But for now, don’t be scared. Get in there, tinker a little bit, make your bike work better. Adjust it for altitude, adjust it for track conditions. Read your manual, it’s pretty easy stuff. All right, and this is Transworld Motocross’s How To, presented by Bike Bandit. Get on it.