I have a 03 z400, When I bouth it I put on a LRD, K&N, Pro Flow, and rejetted (147.5 main), and removed the lid. I live at 5000 feet. I have had a problem with it idiling rough ever since then. I have tried adjusting the air/fuel mixture screw in many positions and have not got it dialed in any better. It runs great everywhere but at idle, it almost sounds like it has a little lope to it. Has anyone else had similar problems, or any suggestions.

 

Did you adjust the needle?

 

Did you happen to take the time to break it in? From your description and the altitude that you live at my guess is that you have to large of a main jet. Since you say that you put in a 147.5 jet I presume that you did not buy a jet kit?

To tell whether your to rich or to lean, remove the seat and start the Z (adjust the idle speed so that it stays running) Now get out your roll of Duct Tape and start placing strips across your airbox closing off the effective air opening little by little, if it gets worse or dies you are to rich, if it gets better then you are to lean. Leave the tape in place at whatever point you are able to determine rich or lean, then change the jet in the direction needed. If you had bought a jet kit it would have come with the smaller size jets along with a couple larger than the one you are currently using, as well as an adjustable needle that helps in fine tuning the exact mixture. Hope this helps and let us know how you make out!

 

Sandneck, Your jetting is lean. I have help put on 3 of those LRD pipe and K/N filter kits. With the lid off, we use a 160 main jet. We have raised the stock needle but found the Z likes the stock placement best.

 

thank all of you, to answer your questions, no I didn't mess with the needle, I was under the impression that it was best in stock position. I was told, from a reputable guy at a reputable shop, who has had some exp. with it in our elevation, that the 147.5 or maybe a 150. I tried the 150 and had the same results. I will try the duct tape thing and go from there, thank you again. What elevation are you at with that 160 main?