2003 YZ450F Jetting


1 reply to this topic
  • KYZAAC

Posted May 15, 2012 - 10:36 AM

#1

i was looking through the jetting data base but didnt find what i was looking for. i bought the bike used, the guy said the bike was just rebuilt before he bought it, he said it was bored out and aftermarket cams, but he didnt seem to know much about bikes.

i don't know what size jets the carb has now, i just ordered a carb rebuild kit.

im having erratic idle problems now, one minute the bike is reving pretty high, i'll pull in the clutch to slow down and the bike will stall, then it will rev high again etc.
i also have a TON off popping on decel

i live right on the atlantic ovean, my altitude is 40ft above sea level.
any idea what the best settings are for that altitude?

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  • grayracer513

Posted May 15, 2012 - 11:19 AM

#2

im having erratic idle problems now, one minute the bike is reving pretty high, i'll pull in the clutch to slow down and the bike will stall, then it will rev high again etc.
i also have a TON off popping on decel


Ignore the decel popping for the time being. Start by checking the clearances of your valves. If your intakes are tight, that can cause an erratic, hanging idle.

If the valves are OK, then you're most likely looking at a partially blocked pilot jet. It doesn't have to be plugged up. Simply having a film of varnish deposited will effectively reduce the size of the jet to the point where the bike won't run right. Start by trying an adjustment:

http://www.thumperfa.../jetting.htm#PJ

Note the results of this adjustment and check them against this info:

http://www.thumperta...ad.php?t=327405

If the indications are that your pilot is too small, start by cleaning it.

http://www.thumperta...726#post8021726

This is the stock jetting:

Main Jet: 165
Pilot Jet: 42
Starter Jet: 72
Fuel screw/Setting: 2.0-2.5 turns out
Needle/Position: NCVQ-4

If you find a great deal of variance, between what you have and the stock stuff, start by returning it to stock, with either a #42 or #45 pilot.

If the bike still pops excessively (some is normal) after you get it running right, first look at the exhaust system and be sure it's not leaking air. This typically happens at the mid pipe/header junction or at the head.





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