No more BKmod on 2003 WR450s
Posted May 19, 2003 - 05:56 AM
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.
Posted May 19, 2003 - 11:14 AM
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.
Posted May 19, 2003 - 10:29 PM
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.
Posted May 20, 2003 - 05:21 AM
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...