Jetting Ride Report

19 replies to this topic
  • utvols

Posted February 03, 2003 - 05:26 AM


I raced my bike in a Midsouth Winter Series Race yesterday and noticed the following about the bike. I had a bad stumble off iddle past 1/4 throttle. The bike would not lug and several in instances stalled while trying to accelerate. You had to feather the throttle to get in upper rev range. The starting was excellent in all situations. I would describe the throtle response as very lazy and loaded up feeling. Once you got past the stumble the bike rocked. Quarter to full throttle response was awe inspiring. This is the fastest dirt bike I have ridden. The power was very linear and the suspension soaked up everything with the brakes working very well.

I will be going back to a 45 pilot jet to see if I can clean up the bottom end. I suspect the combo of the starter jet and pilot jet are to much. For now I am leaving the starter jet alone since the bike starts so well and this is the same jet in the YZF. I just cant figure how the YZF gets away with an even smaller pilot jet. The bike was definately lean when I broke it in and I had no popping or back firing at all yesterday.

I would really like to hear other peoples experiences with jetting. I know I am close and would like to get some input from others.

  • r1superstar

Posted February 03, 2003 - 05:35 AM


I'm running a 45 PJ and I ride at 4000-8000 ft. It works great. The 42 was way too lean.

  • Jim_Patterson

Posted February 03, 2003 - 03:19 PM


I followed your suggestion and changed to 48 pilot and 160 main jet, but I didn't change the starter jet. My bike starts easily and throttle response is good thru the entire range. I havn't ridden it enough to be sure it will stay this way. I might consider plus 1 or 2 increase in pilot jet or a clip change on the needle. Personally I don't plan to change the starter jet unless several people do it with good results.

  • dukeboy

Posted February 03, 2003 - 04:36 PM


I have a 155mj and a 48 pilot,my clip is also moved down 1 position.The air/fuel screw is out about 1 5/8 there about.I normally ride anywhere from 500 to about 4000 feet. I just did this on sunday, and rode it a while, and so far its alright. I god rid of the hiccup it had when holding the throttle in one place(10-30 mph).hope this helps! :)

  • dukeboy

Posted February 03, 2003 - 04:41 PM


I forgot to say that I also did the grey wire mod. This could have something to do with it?

  • adamwagar

Posted February 04, 2003 - 12:32 AM


Maybe this is a dumb question, I'm a bit of a mechanical misfit. Does the starter jet only effect starting?

  • michaeltrundle

Posted February 04, 2003 - 03:32 AM


The starter jet is the jet that is used when you pull the choke on to start the bike when its cold!
It allows more fuel through which richens the mixture up until the motor has enough heat in the cases to vapourise the incoming fuel.
When the engine is still cold some of the fuel slides along the walls of the inlet tract in tiny droplets instead of atomising and burning properly and this makes it lean and hard to start.
The starter jet or choke jet, does not have any effect on your jetting or performance when you are riding as it is completely closed off when you push the choke back button in.
Hope this helps. :)

  • adamwagar

Posted February 04, 2003 - 04:26 AM


Great explination. Thanks. :)

Now, one more time. Seems like going a bit richer on the starter jet would only be a plus. Should not affect your choice of pilot jet, should it???

  • utvols

Posted February 04, 2003 - 04:58 AM


I ordered the YZF needle yesterday and should have it here today. Just for fun I am going to try the complete YZF set up to see how this works. I will have a full report as soon as I am through. I noticed yesterday when I cleaned the bike up and started playing with the jetting again that this bike has a very short throttle twist from closed to wide open throttle. My problem is definetly the transition from pilot circuit to the main jet and I want to see if a different taper needle helps this. If it does not I will probally pull the #72 starter jet and go back to just the #48 pilot and #160 main like Jim.

Thanks for the replys I will post results soon.

  • r1superstar

Posted February 04, 2003 - 05:45 AM


This is what I have and it runs pretty damn good. But it could be improved upon a little. 45PJ (42 was stock), 75PAJ, Stock needle #4 position, 168 MJ (165 was stock), 200 MAJ, PS 1-3/4 (2-1/8 was stock). I am also running a hotter spark plug.

My 02' WR 426FP has the gray wire mod, baffle out, and lid removed. I ride anywhere from 4300 ft. to 8000 ft.

I am going to try a different needle.

Just a suggestion. I turn the throttle three times when starting it cold and pull the choke out as well. It fires right up.

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  • Jim_Patterson

Posted February 04, 2003 - 06:47 AM


Is your bike Canadian? Your stock jets are different than what I've seen.

  • Motorod

Posted February 04, 2003 - 06:51 AM


This forum is jetting WR450's not 426's.

  • r1superstar

Posted February 04, 2003 - 11:51 AM


This forum is jetting WR450's not 426's.

Sorry Eh Brah!............Wanna Race?? LMK when you are in town and we'll do it. Laters............db :)

  • Taffy

Posted February 04, 2003 - 12:00 PM


lads would you please put up your jetting and not just put standard jetting or standard needle please as some of us have had to remember about 15 standard needles now and it ain't funny you poking fun at my senial dementure! :)

the reason you boys have got your jetting all to cock is because you have to get it all right and if any one part is out then you're knackered.

it's nothing to do with that hot plug and the hot plug is only useful for lean jetting and never to be used with an enlarged SJ (god forbid!)

if you have a 'Q', 'R' or even an 'S' last letter in your needle it is too fat on the straight at tickover. so to compensate for it you change the balance of your PAJ to PJ (bigger PJ) to make up for it.

so it should be 'P' needle for altitude and an 'N' for sea level even an 'M' like mine so she's well juiced at tickover. this means i can run a low PAJ/PJ as i'm getting plenty past the needle straight. it also means i don't need much help from the APJ when i whack the throttle.

so you need 15 air to every PJ size and PJ's start at #35

#35 PJ wants a #45PAJ
#38 PJ wants a #60 PAJ
#40 PJ wants a #75 PAJ

now the PAS you can buy can be tickled in just a smidge -or out just to keep the ratio but essentially if you're not in this zone then your needle straight will probably be too fat.

when i ran a 'P' (an EKP) to be precise, i would pull off and stall, pull off and feed the clutch, pull off but not gas it. put the 'M' back in and it was always ok.

so a lot of you will be overcompensating with your PJ's and i'm sorry but you've climbed the wrong tree.


  • Taffy

Posted February 04, 2003 - 11:30 PM



  • Rickey

Posted February 05, 2003 - 04:22 AM


I raced this pass weekend at the SETRA enduro. Jetting runs good. You guyes might want to try this. Main# 160--Pilot# 50--air screw stock 1 3/4 out, needle stock. Cranks great, no popping, pulls from the bottom up. Everything so far good.

  • utvols

Posted February 05, 2003 - 04:39 AM



My appologies for not relisting all my jetting. I have in detail gone through step by step what I have done in previous post and do certainly aggree with your point. As mentioned in another post I seem to have bigger problems than jetting right now (CDI appears bad). I will relist my jetting attempts in detail when I get this sorted out.

I gave an abbreviated post since I seem to be doing the most jetting changes right now and asumed right or wrong that people were following the steps I have been taking.

  • Hick

Posted February 05, 2003 - 08:24 AM


I gave an abbreviated post since I seem to be doing the most jetting changes right now and asumed right or wrong that people were following the steps I have been taking.

I'm following you. Let us know how the YZ jetting works out.

  • Jonesy920

Posted February 05, 2003 - 08:28 AM


Not really related but what airfilter are your running? Stock or after market ? I should have my bike down in MEM next week. Maybe we can see if mine runs any different with the same jetting. Btw doesn't the grey wire change the CDI map ?

  • Jonesy920

Posted February 05, 2003 - 08:37 AM


I noticed that the Euro models run #160 main #48 pilot, same as you are running but the Euro needle is #DUQ richer than the US #DUT. My thought is since the WR has a different Map and I think Cam the YZF jetting may not work but the Euro jetting/needle should. Of course non of this matters if the CDI is the culprit. Is there a post on the 450 side to check the Box ?


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