I recently purchased a YFZ and currently live at ~5000ft in New Mexico. I put about 3hrs on the bike in stock form. It ran fine with the exception of some subtle popping at low rpm deceleration. Stock jetting appears to be ok at this elevation. I just installed a the pro flow kit with the foam filter and removed the airbox cover. Stock jetting on mine was 42 pilot, needle on 4th slot, idle screw ~1.5turns out (by the way it is not capped as some dealers may claim), and a 158 main. I went up to a 45 pilot, needle on 5th, 2.5turns out, and a 170main. As it turned out it was too rich with it most noticable at 0 - 1/8 throttle. I checked the spark plug electrode after running it and it was black. I haven't tested full throttle circuit since I am still breaking it in. Anyway I put the 42 pilot back in and installed a 165 main. All these adjustments are doable with the carb installed if you have a short narrow flat head screw driver. The carb is relatively simple to remove if necessary. It is now running perfect, at least from 0 - 1/2 throttle. I have not looked at the plug but I suspect it will be ok. There has been alot of discussion about how lean the YFZ is in stock form. I suspect it is ok for higher elevations, but a little lean for 0 - 1000ft. Has any one had any experience with jetting this at 5000+ft? Oh there is a noticable difference with the airbox lid off. Thanks for feedback.

 

FYI -

At 5000 ft elevation, stock with pro design filter kit (foam filter) with air box cover off, 45 pilot, 1.5 turns out, 165 main, #4 on needle, running perfect. If only Yamaha could have set it up correctly from the beginning.

 

Hey, are you doing this with the exhaust baffle taken out? I ride at 5000 feet and I'm sure I'm a bit lean with lid off and baffle out. One guy I talked to said he ran jetting exactly like yours at 3600 with baffle out lid off and was right on.

 

I usually ride at 5000' also and currently it's jetted for about 1000' with 45 pilot, YZF needle I think on 3rd slot, and 175 main. It runs a little rich at 5000' so I'm guessing around a 170 would work well. I have GYTR pipe, K&N, and lid off. If you're running the stock pipe, then around a 165 should work pretty good. I would go back to the 45 pilot jet.

 

from what i have seen at sand mt. nevada (4000ft) the fastest yfz's run yz needle #3 clip, 48 pilot, 168 main and 2 and a quarter on the mixture screw. This is with KN kit and full system pipe

 

Sorry to bother you, but i was wondering if you could help me out. I live in WA state sea level and am planning a trip to South Dakota at the end of the week. I have a 05 yfz 450 with a gytr pipe and a k/n filter without a lid. I am running a 170 main and it runs fine here. what do you think i should run for a main at 5,000 feet? any help would be great. thanks Joel