No more BKmod on 2003 WR450s

6 replies to this topic
  • timvv51

Posted May 19, 2003 - 05:56 AM


Since the BKmod is no longer needed on the new WRs I guess the whack the throttle stutter is gonna be jetting. Can someone tell me what I should do with the pilot AIR jet to help richen the pilot circuit. I have a 70 in there now and a 48 pilot jet. I am going to a 50 pilot jet. I have heard of people running 100 pilot Air jets. Does this going up to a 100 Air jet richen or lean the pilot circuit? There is no discussion of this in the manual. Also been seeing posts with people running the stock YZ needle. Has this helped the stutter? Can you tell I hate the stutter? Thanks Tim

  • Hick

Posted May 19, 2003 - 08:14 AM


I guess the whack the throttle stutter is gonna be jetting.

Yep, and it is probably needle and/or clip position.

The Air Jets sort of go hand in hand with their respective fuel circuits. Typically if you change a fuel jet more than one size you will need to go at least one size in the same direction with the air jet, but this is just a general rule. If the WR 450 is anything like the 400s and 426s, it isn't jetted very well stock due to the restricted air box and exhaust.

But a 100 PAJ should be a better match for a 45-48 pilot. You can get an adjustable PAJ screw from Sudco, that way you only have to buy one part.

If it were me my first instinct would be to just scrap the entire WR setup and jet it just like a YZ (mainly a needle change) and go from there.

To answer your air/fuel jet question, a bigger air jet will tend to lean out the upper rpms. If you have a lot of surging at constant speeds and/or too much popping during decel, you need to be richer (smaller) on the pilot air jet (high rpm / low throttle). If your PAJ is too small you will feel some sputtering at constant speeds (mid to high rpm / low throttle).

Hope this helps.

  • Rich_in_Orlando

Posted May 19, 2003 - 11:14 AM


Bigger Pilot air jet = richer pilot circuit
Bigger Main air jet = leaner open throttle jetting

My bike had a problem with fouling plugs at idle for a little while last year. I took the carb off to clean it and realized I had the pilot air screw open twice as much as I should have. For a 35 pj, it's recommended that you run equivalent to a 45 paj, which is 1/4 turn out on the pa screw. Mine was 1/2 turn out. I adjusted it properly and plug fouling went away.

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  • Taffy

Posted May 19, 2003 - 10:29 PM


although one shouldn't argue with your results rich, i have to say pilot circuit which is 2nd/3rd gear area goes

if you lift the air you lean and if you lift the jet you richen. also vice versa.

i can't reach jetting Qs anymore can anyone else?

anyway there it will tell you that the PJ and PAJ should go hand in hand as pairs. however if you have a dreadfully lean needle straight diameter, you will have to compromise this ratio. in other words a small PJ becomes a big one just to help the bike tickover.

all along what is needed is the right needle straight.

in the UK a 'M' or 'N' will do and i hear that at altitude in the states it's more like a 'Q' or 'R'. the correct pilot jet at any altitude should be around 35/38/40 and any bigger is coz of that big fat needle.

this is all pre 450.


  • timvv51

Posted May 20, 2003 - 05:21 AM


Hi Taffy: I am assuming that I am still a little lean on my pilot circuit because I get some popping on deceleration. The bike runs like a stripped butt ape (very good)except for this darned hesitation when you whack the throttle. I am assuming this is because of the lean pilot circuit and probably too lean needle. I know how to deal with the needle, thats no problem but the pilot jet, pilot air jet relationship is new to me. From other posts I am gathering that if you richen (go up numerically on the jet number) the pilot jet, you should also richen (go up numerically on the jet number) of the pilot air jet. Correct me if that is wrong please. I plan to get the Sudco pilot air jet so it is easier to adjust but I need to know which way to go with it too. Also for the benifit of us Colonialists that are Kings English impaired what is tickover. Tim


Posted May 20, 2003 - 08:25 AM



Dammit man....... I heard someone buried you out on the football pitch somewhere.

Good to hear from you...

Bonzai :)

  • Rich_in_Orlando

Posted May 20, 2003 - 10:52 AM


Link to Jetting Q's


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