I have a 2000 honda 300ex, all stock, except with a cobra 4 stroke sysems exhaust. MY pipe is backfiring, and some one told me this means i am "running lean" and that i need re-jetting, could some one please tell me how to do this?

 

To be honest, I am not a big fan of the cobra exhaust, they are pretty loud and obnoxious, but anyway, to answer your question, rejetting is fairly simple. Take your rear fenders off ( latches in back by the grab bar) to give you access to the carb. You will need to loosen the clamp from the air box snorkle to the carb, and take off the front to the motor as well. If you feel you need more room, you can remove the entire air box. Shut off the gas to the carb, and you can drain the carb using the screw near the bottom,near where the hose comes out, this will empty most of the bowl on the carb. A little twisting of the carb will pop it out of the intake boots,and you will be able to turn the carb and see the bottom. There will be 4 small phillips screws holding the bowl on, remove them, and take the bowl off. In the middle, you will see a brass screw with a hole in it,some are slotted, some are hex shaped like a bolt. This is your main jet, remove it and see what number is on it. You will need to go larger to make the carb run richer, for example, if your stock jet is a 135, go up 2 sizes to start , a 140, (jets go in sizes of 2.5, 135,137.5,140,etc.) Do a run with your quad, to see if the power picks up, and see if there are any flat spots,or sputtering. Cutting out on the top end usually means it is rich, if it seems to lose a lot of power wide open, you are lean. Once you get it running right, put in a new plug and do a full speed run, then shut the motor down and coast to a stop, pull the plug for the final check,should be a even tan color, white or very pale is still a little lean, brown or black is rich, you can adjust that by moving the needle clip, up to lean it out on top, or down to richen it up. Hopefully this will get you started in the right direction, any one else that has more tips, please add your comments !!!