jetting for low temps 03 wr450


1 reply to this topic
  • tomk

Posted October 22, 2011 - 12:23 PM

#1

hey guys, I have a 03wr450 with the free mods done and a jd jet kit. I am converting it to a snowbike this winter. I will be riding in temps mostly from 10-20f what suggestions do you have for jetting? oh I am at 1000 ft in minnesota do I even need to change anything. I am sure I do, i know two stroke jetting pretty good but this is my first 4 stroke, also what about at elevation out west 6-9000 ft

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  • ColoradoTim

Posted October 27, 2011 - 10:27 AM

#2

The 2003 WR450F is the most difficult bike I have ever jetted. Adjustments also vary from bike to bike. My first solution was to remove the accelerator pump adjustment screw as it dumped too much fuel and bogged the bike. Then following the rules of 1) leaning it out for higher temps and/ or altitude, and going richer for lower temps and/or altitude. When this didn't work right, I changed the needle to a stock 2003 YZ450F at the 3rd position (a friend gave it to me and as nothing else worked, I tried it and it worked). Dropping the stock needle to the 3rd position has worked for many people too and it was close for my bike, but it still had a slight bog. Have the gray wire off for MX and on for enduro and this does not effect the jetting.

The last few years my bike has been at 155 main and 42 pilot, riding up to 12,000 feet. The 10% ethanol and no high octane gas in Colorado problem is solved with octane booster and keeping the gas fresh. Going to Moab, UT this weekend and will go back to stock Canadian 160 main and 48 pilot as it's lower and colder.

Here's a chart I found for 2003-04 WR450F's:

This recommendation requires air box flow mods and an open stock or aftermarket pipe and ACV circuit intact.

Elevation 0 to 4,000. feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet
45 to 60 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet
60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet
75 to 90 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #50 leak jet
90 degrees plus: 160 main, JD Red #4, 45 Pilot, 2.0 turns, 65 starter jet, #60 leak jet

Elevation 4,000 to 8,000 feet:

30 to 45 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet
45 to 60 degrees: 168 main, JD Blue #3, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet
60 to 75 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #40 leak jet
75 to 90 degrees: 165 main, JD Red #5, 45 Pilot, 2.0 turns, 65 starter jet, #50 leak jet
90 degrees plus: 160 main, JD Red #4, 45 Pilot, 1.75 turns, 65 starter jet, #60 leak jet


Elevation 8,000 to 11,000 feet: ( Note you will loose a lot of power due to altitude but your bike will idle and not foul plugs!)

45 to 60 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 70 starter jet, #40 leak jet
60 to 75 degrees: 160 main, JD Red #4 , 45 Pilot, 1.75 turns, 68 starter jet, #50 leak jet
75 to 90 degrees: 158 main, JD Red #3, 45 Pilot, 1.5 turns, 65 starter jet, #60 leak jet




 
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