jetting 426 at 4,000 ft.

1 reply to this topic
  • Hick

Posted June 29, 2000 - 02:05 PM


Anybody out there live/ride in high desert elevations? I ride in New Mexico, mostly over 4,000 ft. Climate is hot and dry. Every two stroke I have had needed significant rejetting to run well but because YZF ran pretty good right out of the box I only went one size leaner on pilot and main, dropped clip one notch & fuel screw in 1/2 turn from stock . Plug looked better, bike started easier but I still had hesitation when throttle is chopped on so I went back to stock clip position.
Not sure if this helped or if I just got more used to it. Still hiccups if you chop it at low revs. Is this effect of accelerator pump and can't be cured? Anybody who rides in altitude/climate/conditions like mine please reply w/ your best 426 jetting. I am also now running PC T-4 exhaust and love it. It seemed to richen it up a bit but after one race (which was at even higher alt. like 6,500) the jury is still out on its effect on jetting since I haven't ridden since. Any comments on exhaust sys. effect on 426 jetting? (PC or other aftermarket).

Also, manual says that if pilot jet is changed then pilot air jet may need to be changed. My dealer is retarded, has anyone ever heard of changing air jets? There was only one part number at the HLSM Yamaha parts site (from earlier post, kick ass site, already ordered some fasteners and stuff, thanks whoever it was for that info.) I am wondering if smaller pilot air jet will cure the hiccup.

Great forum, my first post, thanks in advance!

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  • JBM

Posted June 30, 2000 - 06:02 AM


I ride in New Mexico as well, at about 3500 -5000 feet. I am running a 165 main, 45 pilot and fuel screw about 1 3/4 to 2 turns out. I went with a 48 pilot at first but was too rich with hot weather and altitude so I went for the middle 45, between stock and a 48. This has worked well so far. If you are going any higher than 4000 feet you may want to try the stock settings. For me I have not noticed any hiccup or hesitation, although I've heard of people getting this.

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