Jetting for high compression
Posted May 16, 2003 - 02:28 PM
Posted May 17, 2003 - 04:17 AM
Be prepared to take the carb in and out 5 - 10 times over a weekend of jetting. Forget taking it to Taffy's level. You need to get your bike in the ball park first. Bog above 3/4 throttle should be a sign of rich jetting. If it stops pulling hard at full throttle you are lean on the main jet. Start with a newly gapped spark plug, 160 main, stock needle in the center clip position. I like to jet by the seat of the pants. Make sure you have run the bike for 5 minutes hard so it is good and hot for your evaulation. You want it to pull hard & climb revs smoothly. I am sure someone with a moded WR400 may have a better start point. But I have seen some ridiculous rich main jets on this forum. Some run as high as 185 mains. I suspect they have YZ timing and can run richer. I can not go higher than 172 main at sea level in 30 to 40 degree weather. Hope this helps. Good luck
Posted May 17, 2003 - 07:41 AM
the jetting on your ported and HC piston bike should be lower than normal by 2 or at most 5 on the MJ. otherwise just treat it the same as all the other WR400's you've seen jetted. my jetting is good for sea level or you can be a little more conservative with something like a 38PJ and EMN needle and a 165 on that open pipe. the rest-copy mine if you want.
if you're above 2-3,000ft then go start following people like hick and whoever.
Posted May 18, 2003 - 04:31 PM