It may be necessary to change the size of the jet in your carburetor. Perhaps the weather has changed, the altitude id different, maybe you put on a different exhaust pipe. Things like this can cause your motor to run "lean" or "rich". Then your motor will run like crap, or even seize. That's bad. an easy way to know if your 2-stroke engine is running lean or rich is to take out the spark plug and look at the electrode. If it looks white, you're running lean (not enough fuel). If it's black, your running rich (too much fuel). You might also notice that you're running lean if you give full throttle and the motor seems to not want to respond. If you're rich, the motor will be boggy and make a noise like a sick goose (referred to as 4-stroking). anyways, let's jet your bike.
I'll show you how to do it.
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Step 1: What Choo Need
Step 2: Turn Off the Fuel...
Step 3: Remove the Carburetor
Step 4: Unscrew the Float Bowl
Step 5: Remove the Jet
Okay, time to put in your new jet. There's going to be a tiny number stamped onto the jet. Good luck reading it. If you are running lean (your spark plug is white), then your new jet must have a higher number than what is stamped on your old jet. If you are running rich (your spark plug is black), then your new jet must have a lower number than what is stamped on your old jet. How much higher or lower? I have no idea. You're going to have to start trying jets until you find the right one. As a general rule of thumb, you should start with a jet that is too big, so your motor "4-strokes" (that sick goose noise) and then start working your way down until it stops 4-stroking. Then fine tune.
Step 6: Take Your Top Off....
Step 7: Needle Adjustment
Once it's back together, you need to look into the top of the carb for the little bump that will line up with the valley that runs on the side of the throttle slide. The throttle slide needs to be put in so that these line up, or else it won't go in. Once everything is together and the top is screwed back on, pull the throttle control and look through the throat of the carb to be sure that everything is moving properly. It is? Great.
Take off the carb, put BACK IN the next size smaller jet, take off the top, move the clip BACK UP ALL THE WAY TO THE TOP of the needle, put it back together and you're done. The motor should no longer be 4-stroking.
That was a total pain in the butt, wasn't it. Yes, it was.
One thing that I forgot to mention is, it's kinda hard getting the choke slide to fit back together when reassembling the top portion. What I do is, line up the throttle slide with the bumb and start it in 1/2 way. Put the choke slide in its track THE RIGHT WAY, hook it to the choke rod and then put the top on. Be careful not to tear the gasket. Sometimes the throttle cable pops off and you need to take it apart and try it again.
After you've done this a few times, it gets much easier.