Newbie needs help with jetting (low altitude)

I'm seeking advice on changes to my jetting. Two months ago, I purchased a used (only 55 miles) 2002 WR 426. I have done the following mods: removed airbox, removed baffle, cut grey wire, and shortened throttle stop. I ride in East Tennessee at altitudes ranging from 400 ft to 1100 ft. I am currently not pleased with the bike's performance. It does not have a crisp throttle response, especially bogging at low end. I also get some popping when coasting downhill in gear. I don't know all the numbers yet, but all my jetting is currently stock. I run premium gas, and keep my stock airfilter clean. I haven't checked my spark plug yet. I have done a lot of research on jetting here on TT, but most of what I have seen refers to higher altitudes. I am hoping to hear from LarryCO or Taffy, as it appears that they are somewhat of jetting legends around this place. What should I change to? I really appreciate the help!

1- Do the BK MOD and adjust the squirt to @ .5 seconds

2- The popping on decel can be cured by turning out the fuel screw located under the carb on the engine side.

3- Now that you uncorked the WR, it's basically a YZ. I suggest changing your timing to YZ spec. This gives the bike a more abrupt midrange hit. Changing your timing does not require new jetting.

4- Try a new E series needle, OBELN or OBEKN, and start at the 3rd clip. Start with your stock jetting, 42 pj/75 PAJ

165main/200 main air, 1.5 turns out on the fuel screw. You may need to jump to 168 main in the summer

Are you running an open pipe or an insert? I run a Baja Vortip in the 02 426, a little above sea level. Jetting is stock, needle on clip 5. The stock setup popped a little on decel, I moved the needle up one clip and cured this. Turned the fuel screw in approx. 1/2 turn and the bottom cleaned up alot. The bike is outstanding on all throttle positions. I also agree that you need to check your squirt duration and do the BK mod if its over .5 sec.. If you run the stock baffle you will not be able to get the bike to perform. If you run an open pipe I think the E taper needle will work the best. With one of the good aftermarket baffles you can get great response from the stock D needle. If you go to the E taper you should drop the main jet to approx. 160. Good luck

I agree TC OPEN pipes benefit from "E" tapers better than restricted pipes such as stock set-up (plugged)I found out as well that on my particular bike with a Vortip like device in a YZ silencer that the "D" taper does rock.The only thing I have'nt tried yet is the "Taffy" style jetting.Harem has good starting ponts for OPEN exhaust with the lid OFF. :)

Michigan has similar altitudes to you, our average elevation is about 700 ft. All my info is in the signature however I have a 2001.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now