Michigan Jetting

Anyone that rides in Michigan or similar climate, what are your jetting specs, and how does your bike run. Free mods done (in signature) and have stock jetting. From gaining info from previous posts, I think my bike is running lean especially when temp drops. Just curoius on what others with my climate conditions use for jetting. Thanks

Onyxxx,I have a Canadian WR,just put on a YZ silencer.I rode last weekend in Maumee Ohio,it was about 60 degrees.Stock jetting seems lean.Had to go out over 2.5 turns on my pilot screw.I think I'm going to try OBELN needle and see where that takes me.I think the bike needs at least 45 pilot and maybe 168 or 170 main depending on needle position.Just a little mental masturbation :)

Im on the south west side of Michigan. My 99 yz400 is running stock jetting still. It runs great. I go bigger on the main, usually 1-2 sizes, in the winter to compensate for the denser air. I do have a lean condition on the bottom. I let off the throttle and it popps. But it dont seem to be hurtin anything and I aint fowlin plugs so I aint messin with it.

I wrote a jetting spreadsheet that predicts how your jetting will change with different temps and altitudes. Garrett's website has it (but he didn't post directions) or you can get it at my website:


Yeah, same one but it is a downrev, Garrett asked me if he could put it on his website.


I live near Detroit and ride trails all over the lower penninsula. The settings and mods listed in my signature have been working great for me. I was fouling plugs for a while and it was hard to start until I got it figured out with the help of James Dean's spreadsheet and some research. I probably could have gone down on the main jet a size or two during the summer but how often am I really at full throttle in the woods when the trails are barely handlebar wide.

I can't say if the 01 will be the same as your 02 but should be similar.


Just wondering why you went richer with the pj and mj. I thought that the obeln needle would make things richer and you would have to possibly go leaner if anything. I see that you did go leaner with the paj. I also noticed that you have done the BK mod, is that why you went richer? I ride in Gaylord, mostly in the summer. Thanks for the Info.

Originally I just searched out some jetting settings here on the board. I found some recommendations by James Dean to someone in similar climate and went by them.

At first I used a 45 PJ but was to rich and then went down to 42. I probably should be running a 165 main or one smaller for the summer.

The theory is that opening up the airbox and putting on the Vortip I had leaned out the mix by allowing more airflow, I needed to compensate for the extra air. By the way if you ride in the trails here in Michigan you need to pass 94dB sound limit, and the uncorked stock exhaust won't pass.

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