jetting frustration

3 replies to this topic
  • Descendents

Posted September 14, 2003 - 01:27 PM


I finally had some time to ride this weekend and went with JD jetting blue #4 with 168MJ, FS anywhere from 1.5 to 2, with rest stock. I put on about 25 miles with this setting. My pipe was pretty red and were the head pipe connects to the mid section, the mid pipe that cover the head where it clamps was red. The bike was good down low then I would say the end of third gear and fourth gear felt like I was running out of power to quick. When I would shift from fourth to 5th gear it felt like kicking into overdrive though. When I got home I pulled the plug thinking it might be to lean and the insulator was totally white and the elctrode was a little whitish. The tip of the plug was tannish then went down to carbon black with the rim being carbon black. The bike did not pop or bakefire, just power wise felt like I was running out on the top end. The temp was about 75 at 1000ft where I ride. Would going from a 168 to 170 mj make a significant difference? I have not been able to dial my jetting yet this summer, it either fouls out or now running lean. The one thing I did solve is when I had the ELN needle in with rest stock, I would get studders in it when going through 1st 2nd and somtimes third gear, but the top end was great. So I must of been rich before on PJ with the cutting in and out. I don't have that going through the gears now but I just want the bike now to feel like the mid to top end that I had with eln with the jd jetting.

TcTrailrider - If your out there, since you ride in my climate, just wondering what you have been running now in your carb. How is your top end like fourth gear and fifth gear. Like I said above it felt like I had no fourth gear this weekend, it was always a quick shift, actually when shifting from even 3rd to fourth with eln use to feel like a huge pull, it just wasn't anywhere close to that this weekend.

  • tctrailrider

Posted September 14, 2003 - 03:49 PM


I am running the Red 5 42PJ and 165MJ, with a baffle. Very happy with it. The baffle will have an effect mostly on higher throttle settings. You say you are stock jetting on Blue4. Stock is 42PJ and 165MJ. With an open pipe my guess is that a 170 or 172MJ would work the best. If you ran the stock D taper needle with the open pipe 170 or 172 would be good. The E taper needle has a smaller tip and requires a smaller MJ than the D. The JD needles begin and end like a D taper. The straight and tip are the same size. The difference is the taper is cupped, causing JD's needles to become richer than the D once on the taper and gradually leans back out towards the tip. This is no doubt an overly simplified opinion but I think reasonably accurate. The D taper as well as the JD needles need a MJ about 5-7 larger than the E taper.
If you go to a 170 or 172 this will also slightly richen your lower throttle settings. So go up on the MJ and see if the power picks up. If you go to rich it will miss at WOT. Also your sig. says 38PJ, if this is true you may want to go back to the 42. Have fun.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • tctrailrider

Posted September 14, 2003 - 03:54 PM


Also I think your Blue 4 will be better than my Red 5 with an open pipe.

  • Descendents

Posted September 15, 2003 - 10:22 AM


Thanks for the info. My carb setting was blue #4, 168mj, fs 1.5, rest stock. The p-38 in my signiture is the p-38 lightning( instead of doing bk mod). Next time I get up north I will try 170 and 172 mj to see if it cures problem.


Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.