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Yz490 Jetting
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Posted by: JWW0846
Any One Running A Keihin 39pwk On A Yz 490,
Wondering About Jetting Specs????????
Thanks
Posted by: DEANSFASTWAY
What are you using for air boots and intake I thought of this for a evo bike but they dont allow flat slide carbs . If I were to try it Id think like 55 pilot 170 main 6.0 slide or so. dont take these as specs butthats what Id try first.
Posted by: JWW0846
I Have Put My 1990 Yz490 Motor In A 2001 Yz250 Chassis,it Works Realy Great........
Just Trying To Update Motor A Little ......
Posted by: DEANSFASTWAY
jimics is doing that with a YZ400F 99.
Posted by: 490Dave
I hope your '90 490 motor is better than my '84.
I have just plain given up on that thing after two bore jobs, two pistons and many hours of trying to figure the jetting out i have come to the conclusion it just cant be done without professional work from EG or the likes. Im savin my money for a late model YZ250.
If you need any parts let me know..
Good luck.
Posted by: JWW0846
What Carb Are You Using ,i Can Probable Help You Out .
I Have Been Riding A 490 For Years And Never Had Any Problems With Reliabilty..
Posted by: ruling the roost
490 dave check 4 air leaks i had a it 490 and lunched it couple times before i found an air leak in intake manifold then it was reliable :flame:
Posted by: DEANSFASTWAY
They suck base gaskets really easily too. run a bead of sealer at base of cyl.Once you get them going good theyre pretty reliable .
Posted by: 490Dave
The Carb is a 44mm Mikuni, On the second rebuild i sealed everything up pretty well and the base and head gaskets leaked a bit then sealed up after retorquing, then the exaust started leaking. The only other leak on the intake side was where the throttle cable nippled up into the top of the carb. I used all new gaskets and yamabond sealer. The wife has pretty much nixed trying to fix this one again, but suggested looking for something newer 
Posted by: JWW0846
Try This Jetting 3.5 Slide,q8 Needle Jet,stock Needle 2nd Clip,50 Pilot,440 Main...
Mix Yamalube At 60.1..
Eric Gorr Gave Me These Settings And My Bike Has Never Run Any Better,no Pinging And Great Throttle Response
Good Luck
Posted by: 490Dave
That sounds about where i started. Im at about 6000' and know im gonna have to go lean.
Thanks
Dave.....
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