450F Air Screw

3 replies to this topic
  • GreggT

Posted November 24, 2004 - 10:58 AM


I can turn my air screw ALL the way in without much difference. What is it telling me?
Is the jet too rich?

  • grayracer513

Posted November 24, 2004 - 01:15 PM


First, it's a fuel screw, not an air screw as it would be on a 2-stroke or an older 4-stroke, so it gets richer as you back it out.

Second, if you can't get a decent idle betweem 3 quarters to 2 turns out, you may have another problem. Check your valve clearances, and check the condition of the rubber neck the carb clamps into.

If that's OK, and it doesn't seem too lean at a half turn or less, then you should drop a size on the pilot jet.

Check this out, too:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • GreggT

Posted November 25, 2004 - 07:53 AM


Well, The URL you referred me to calls it an air screw. But Fuel or air what ever. If it run clean with the needle all the way in I suspect I need to go to a smaller jet.....right?

  • BC3

Posted November 25, 2004 - 11:47 AM


Hey GT, Happy T day Bro. What year is your bike....I have a 03 YZ450 and
it seems to be pretty happy at around 2 turns or so...If your idle is too high
you will start to get into another circuit and will make you think your FUEL SCREW is the problem...remember your carburetor has four circuits that when adjusted properly should over lap and make a smooth transition through out
the rpm range....So what this means is before you decide that your rich/lean
on your pilot jet......make sure the idle is turned downed to where your only
opearting on the fuel screw circuit......Im sure you will see what Im talking about will help you figure it out...good luck.

BC :cry:


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