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Author Topic: Rebuilt HIF4 Carburetor Problems  (Read 70 times)

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september2020

  • An AMGBA Club Member
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  • Posts: 14
Rebuilt HIF4 Carburetor Problems
« on: August 09, 2020, 01:35:01 PM »
I have a 1973 MGB with original, recently fully rebuilt, HIF4 carburetors.

Since the carb rebuild I am having a very difficult time starting the engine when it is cold. 

When the engine is at normal operating temperature it is very easy to start and it runs fine with a smooth idle around 950 rpm.

I am unable to get in touch with the technician who rebuilt the carbs and am wondering if you have any suggestions as to what I could try to rectify this problem. 

I'm wondering how far the fast idle screw needs advance along the choke cam at full choke to ensure full enrichment?  I checked the mixture looking for the 50 rpm blip that you mention in your video.  Not sure if I noticed that working alone without a tach but the engine neither raced or stalled out when I move the pistons with a small screwdriver.  If the carbs are set too lean would that be part of the issue with cold start problems even at full choke?

The service that included the carb rebuild included setting the timing, tappet clearances, new Champion plugs.  The car has Pertronix electronic ignition.

Thank you for any suggestions/guidance that you can provide.

Joe Prior
Toronto, Ontario, Canada


JohnTwist

  • AMGBA Club Tech Staff
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  • Posts: 83
    • University Motors
Re: Rebuilt HIF4 Carburetor Problems
« Reply #1 on: August 09, 2020, 01:43:46 PM »
When you pull the T handle choke cable from the dash, it should move as much as two inches.  Ensure that when itís pulled to itís fullest that the interconnecting link between the carbs has rotated the choke cams as far as theyíll move.  That alone makes the mixture so rich that the MGB should start in even arctic conditions!

When setting up the fast idle, pull the choke out until the engine rpm reaches itís fastest.  Usually, if you pull beyond that point the rpm begins to drop.  Then, balance the carbs at an idle speed of about 1600-1800.  Thatís all there is to setting the choke idle.

SAFETY FAST!
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids MI 49506-2410
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SAFETY FAST!
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506

616-307-6737
johntwist@universitymotorsltd.com
www.universitymotorsltd.com

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