Stock YZ pipe

[02WR426Cali]

I was wondering if I will need a jet kit on my 02 WR426 when i put a stock YZ pipe (slip on) on? My bike has the grey wire mod, twin air air filter, zip ty fuel screw, yz throttle stop, and that's pretty much it for the engine mods. It runs fine with an open wr pipe and a gyt-r insert. Will I need a jet kit? If so, which one is the best for the $$?

[bg10459]

You will probably need to re-jet. I went from a completely open WR pipe to the YZ pipe and I needed to re-jet. I went with the JD kit and have no complaints, but a few people don't think they are worth it. You could probably get it right with a bigger mj and pj and maybe raise (lower the clip) the needle. In my opinion, the Zip Ty fuel screw is worth the money because it makes tuning the pilot much easier, something you will be doing frequently while trying to get the jetting right.

[PBDBLUE]

The WR's are pretty lean right out of the box. You would probably benefit from jetting even with the stock exhaust. Without the insert it's pretty open and probably not that much different than the YZ in terms of flow. I run a YZ exhaust on my 04 WR450 with a PMB endcap. Similar power to the open stock exhaust but a bit quieter and a lot lighter.

[bg10459]

Without the insert it's pretty open and probably not that much different than the YZ in terms of flow.

I found that the YZ exhaust required a bigger main compared to the stocker completely uncorked. All things equal, when I put the YZ pipe on I had a terrible high end miss, which was cured with the re-jet. I also had a noticeable mid to high end boost. I think the YZ exhaust flows better.

[dustdogg]

I was wondering if I will need a jet kit on my 02 WR426 when i put a stock YZ pipe (slip on) on? My bike has the grey wire mod, twin air air filter, zip ty fuel screw, yz throttle stop, and that's pretty much it for the engine mods. It runs fine with an open wr pipe and a gyt-r insert. Will I need a jet kit? If so, which one is the best for the $$?

I have the same set up as you. With the free mods and stock un-corked pipe my bike ran pretty good with the stock jetting. After switching to the YZ pipe I soon realized the jetting was way off? . I went with the JD kit because of all the recommendations on this site and I must say that I am very impressed . It is like a whole new bike. I couldn't be happier Just spend the money, you will be happy you did.