WR450 Jetting

16 replies to this topic
  • HighPlainsWR

Posted January 17, 2003 - 06:14 PM


Picked up my 03' WR450 today. Took it right home and did the thermal start break-ins (3X warm-up cool, not too hard when the temp is 27 degrees) and then rode around the block at home. The motor is poping of idle at speed and backfiring constantly under deceleration. Any other 03' WR owners experiencing this? I'm at 6K ft. and the dealer in Denver setup the jetting for this altitude. Past experience leads me to believe the pilot jet is too lean? Any suggestions?

  • ThumperWR450F

Posted January 18, 2003 - 04:49 PM


:D :D :) :D :D

  • dukeboy

Posted January 19, 2003 - 06:00 AM


I have had my bike for about a week now, and yes mine backfires on the decelleration. I have put a thunder alley pipe on it and a uni filter, but it did the backfiring before I did that stuff. I only changed the main jet to a 155.It didn't change a thing. Other than that it runs great. Try to hold the throttle in one spot at slow speeds and tell me if yours kind of sputters. Mine does, I have heard it might be a yamaha thing.Our mechanics that own 02' 426's say theres does the same thing.Happy riding!!!

  • ThumperWR450F

Posted January 19, 2003 - 06:11 AM


i have a 97 dr435 and it pops on decel too. they say it's normal.there is no difference in performance it is just kinda embarrassing... vroom vroom... pop pop pop pop pop !! hopefuly i will let you know about my WR Monday when it is ready !!

  • HighPlainsWR

Posted January 19, 2003 - 06:11 AM


Thanks for the tip. It turns out the dealer prepped my WR450 with a #40 pilot jet, too lean even for 5,500 ft. I richened the pilot circuit by adjusting the pilot screw out one full turn. This lessened the engine speed fluctuation during throttle openings up to 1/4, but I will need to go to a richer pilot jet, a #42 or #45. Interesting enough, my starter switch failed on the second day - product defect ! The dealer installed a starter switch from a Yamaha ATV. If the replacement switch fails agin on the trail I'll have to use the kick start, or hot wire the starter !

  • jim-in-so-ore

Posted January 19, 2003 - 12:53 PM


Mine does the same thing, The non steady throttle thing, and I am at 1500 foot elevation. I haven't messed with the air screw yet. I will of coarse, because tinkeritis will strike. Jim

  • yamaharichey

Posted January 19, 2003 - 01:43 PM


Ditto for mine I'am 4500 Ft. How about starting? sometimes it starts right up other times it does'nt. Do you pull the hot start every time when its warm?

  • HighPlainsWR

Posted January 20, 2003 - 07:54 PM


Broke-in the WR450 yesterday for 25 miles. Included were stop/starts intentional and otherwise. In cases (3X) were I stalled rich coming out of sand washes, I pulled the hot start in gear w/ clutch pulled in and it started - like right now. On my 02'WR426 those events would have been not so great a moment. Other times, like short breaks and and such, just the starter did it. Centerville ? Do you ever ride west of the Green River, UT area ? Iv'e been there riding several times. Great stuff, cuz' Moab is too crowded. That area is High Plains riding - breathing sand and busting open/close a bunch of cattle gates ! On the 02' WR426 I installed a PowerNow and seldom used the hot start. But it wouldn't matter on the WR426 if you sand stalled uphill - it was all ugly ! Electric start, yeah baby ! Incidentally, changin the pilot to a #42 and swapping out the stock unplugged muffler to the FMF Q pipe solved the throttle and sputter problem.

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  • allinson

Posted January 21, 2003 - 05:14 PM


Highplains: Your pilot is 42, what main are you running and what position is your clip. I ride 10 mile. I live about an hour or so from there.

  • HighPlainsWR

Posted January 21, 2003 - 05:58 PM


Allinson: The main on the 03' WR450 is # 155 w/ 3rd position on the clip. I'm looking forward to spring when I came take the unit up high (8K-10k) and see how it performs. The 02'WR426 I sold last month to buy this unit had a #155 main also and performed awesome. Partially, I beleive, to the PowerNow venturi - hardly ever used the hot start circuit. When I can afford it I'll get one for the 450. Speaking of Ten Mile Wash - in spring of 1998 I was riding up Ten Mile in the shallow stream bed and knifed my then 98'WR400 into a pool of quicksand. I saw a pool of standing water, railed it to skim across and the bike stopped - like right now ! I went over the handlebars, ate sand and when I looked back at the bike it was fork first to the tank in the quicksand. The two of us could not get it out ! Fortunately a family of ATVs came by and tow-strapped me out. I'll never forget Ten Mile, but I want to go back there someday. What a great place to live around ! What is the name of that old bar and grill just south of the highway in Green River ? Great milk shakes !

  • yamaharichey

Posted January 22, 2003 - 08:43 AM


Highplains, Are you saying you changrd the pilot jet to a 42 or is that what it comes with? if you did change it, it sounds like you went leaner, my guess was that it was already too lean so maybe I'am wrong. If you did change it what was the results? Also what altitude are you at?

  • SMD

Posted January 22, 2003 - 08:59 AM


I have not actually inspected my carb but the owners manuel show the following specs.
150 main
45 pilot
OBDUT Needle / 4th position
During my intial ride my bike had a very small stumble on the bottom. Once on the main jet ,mid-range to high, the motor is flawless. :)

  • TooFast

Posted January 22, 2003 - 11:25 AM


HighPlains, It's Ray's Tavern

  • HighPlainsWR

Posted January 22, 2003 - 07:12 PM


The dealer changed the pilot to a #40. I think it's too lean so I'm going to a #42. Haven't done that yet. I'll keep you posted. I'm at 5,900ft. Changing to a #42 should richen it up and relievw some of the deceleration pops at high RPM - I think. I'm I way off on this ? I remember I had the same issue on my 98 WR400 five years ago, but I can't remember what the dealer and I did to solve this.

  • HighPlainsWR

Posted January 22, 2003 - 07:17 PM


TooFast: Your'e too good. Ray's it is. Isn't the retro diner on the same side of the highway the "Chieftan". Ate many a carbo there for breakfast before riding. Back in 99' my 86' Jeep Grand Wag-N-Steer broke down in Green River and while it was fixed I roosted all day at Rays Tavern. From what I can remember I partook more in the bar then the grill.

  • allinson

Posted January 23, 2003 - 06:25 PM


Highplains: So what is your final set up? and how well does it work?

  • AK-thumper

Posted January 23, 2003 - 07:20 PM


A DUT needle is pretty lean compared to previous WRs stock jetting, especially the straight section which governs the critical bottom end.

Did they get green sticker certification for this bike? I'm wondering why it's so lean from the factory.


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