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Author Topic: Metering Needle  (Read 191 times)

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Metering Needle
« on: February 14, 2021, 12:55:38 PM »
What effect would having an incorrect metering needle cause in operation and performance?  I recently discovered that I have a B1AF needle instead of a 45H.


Ron Roland


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Re: Metering Needle
« Reply #1 on: February 14, 2021, 01:07:39 PM »
The B1AF is the needle for a TR6.  Whether it makes the MGB run richer or leaner throughout the rpm/load range I don't know.  I'm sure you'll be happier with a new 45H needle.
That said, the jet wears as the needle wipes against it.  You can purchase a new jet, drive the old one out, and drive the new on in -- but not without damage unless you make a special tool to do the job.  So, resize the old jet.  Get a tiny ball bearing -- 1/8" or less.  Place it on top of the jet, place a punch on top of the ball, and give it a crack with your hammer.  This will crush the top of the jet inwards.  Now, drill out the jet with a #39 bit (0.0995") and the jet will be round. 
The better way to do this is to remove the carb, remove the float bowl, and support the bottom of the jet on the bench or vise as hitting it from above without bottom support can allow it to move incrementally downwards (causing a rich mixture)

Hope this helps!

John H Twist
University Motors Online
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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