Pro X N424-21 Series Keihin Pilot Jet

No. A higher number equals a bigger jet and more fuel delivered.

You will receive one when quantity one is purchased.

The stock pilot jet size for a 2003 yz450f is a 42!

This is universal kit, so we cannot guarantee fitment on any machine. You would just need to select the size that you are needing for your machine.

Unfortunately, since there are many things to consider while rejetting your bike, we recommend to look through your owners manual or contact a mechanic for recommended jet sizes.

yes these jets will fit oem carb

Well, not really. There is a lot more to jetting a carburetor than just these 2 jets. There are 4 types of jets in a typical 2 stroke carb, pilot jet, main jet, needle jet, and the jet needle with the clip. I suggest you do a google search on the proper procedure for jetting a carb. (2 stroke or 4 stroke) If your bike is now running bad and it was running fine before, it's probably not a jetting issue. You may have other problems if this is the case. Jets come in a large varieties of sizes and depending on your issues, you may need to go to a smaller or larger jet. The hole in the jets are tiny and a subtle change can make big difference. Also another thing to check is your spark plug color, a good running bike will have a nice tan color on the electrode of the spark plug. Too dark typically means too rich, too light or white... too lean. Better to be too rich than too lean, always. Also research what's called "Plug Chop" which is the procedure for getting the best spark plug reading for color. Remember, weather conditions, altitude, piston wear, etc... will affect a bike's performance. Determine your issue first, and address that problem. If you still need help, there a number of on-line forums in which to discuss options. Good luck Dalton!

Unfortunately, since there are many things to consider while rejetting your bike, we recommend to look through your owners manual or contact a mechanic for recommended jet sizes.

No, these are the Pro-X version. However, we do have the genuine Keihin Jets as well.