Need Help Jetting YZ490J - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 06-04-2006, 06:46 AM
Why Zee 490J
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Need Help Jetting YZ490J

I have a 1982 YZ490J and i need help jetting the carb, i think it's running to rich, its not getting its speed and power and the plug is a lil black/sooty after a ride.

The clip for the rich/lean setting on the needle is on the leanest adjustment, but the bike is still not running as lean as it needs to be.

The bike is bored 20 thou over or .020
The carb has an oversized main jet 450
And the jet needle is not stock either but cant remember the number on it, may have to look at it and post it here.

Hope this is enough info for me to get this yz jetted
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post #2 of (permalink) Old 12-02-2008, 08:32 PM
Vintage Tinkerer
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first of all get the stock specs from the dealer for the proper jetting your bike came with....set your needle clip in the middle, reset your air screw to 1 +1/2 turns out (in the middle of the adjustment range) then try that...dont know if you have cleaned the carb properly, checked float level etc. etc...as the carb has 7 different circuts...not all will affect your bike in the way that you describe...I only use the middle notch in the carb needle ( one above,one below to tune)...usually if the neele has to be put on the bottom notch it should get a jet reduction, if it has to be on the top notch, it needs a bigger jet....the needle of your carb sits inside a neele jet in the body of the carb...it has a taper to match fuel flow with the raising and lowering of the needle....I have found that if you use the top and bottom notches on the needle it throws the needle jet/needle hormony out of wack...perhaps all that you require is to lean out your main jet...dont know what elevation you ride as your description was quite limited...like how it starts...how it runs hot/cold...lots of things would help to diagnose it more accuratly...hope this helps....I do ride and maintain all my own toys as even guys in the shop dont always have the answer....at present ride a 82 cr480r regularly and at present am rebuilding a 83 cr480 from the ground up...anyway...try those suggestions good luck...ride hard....B
post #3 of (permalink) Old 01-26-2009, 03:52 AM
 
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The thing with the 490s is you either have to leave them jetted rich, or jet them to run great and have it seize. Im not trying to be a jerk, but the 490s are horrible bikes.
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