37mm carb on 426

1 reply to this topic
  • Yammer-Hammer

Posted January 28, 2014 - 03:29 PM


Anyone have a clue what the jetting should be with a 37mm carb on a 426? I figure jet sizes would have to decrease because of the greater air velocity and vacuum the 426 creates

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  • grayracer513

Posted January 28, 2014 - 08:40 PM


Look up the stock 426 jetting in the jetting thread and start there.  They were jetted fairly lean from the factory.  You're probably going to have the most trouble figuring out how to correctly jet the needle and the pilot AIR circuit.  The pilot air jet is important because it controls whether the mixture will stay correct at light throttle at all RPM. If it's too small, the mixture will drift rich at higher RPM when you roll back the throttle.  If it's too big, the mixture will drift lean.   When you roll back the gas to maintain a steady speed for a moment, the engine should run as clean and sharp at 7000 RPM as at 4000.


The needle will be tough, too.  The carb will probably have come from a 250F of one kind or other, none of the 400-450 needle, main jet, etc., info will be directly transferable.  You'll basically be starting from scratch.  You could get lucky and have it work without too much trouble, or not. 


This is a good, reasonably simple guide.  You can freely ignore the part about synchronizing since you have only one carb:







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