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Author Topic: Loss of Power  (Read 237 times)

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Loss of Power
« on: February 14, 2021, 12:53:51 PM »
I have a 1974 MGB that has a loss of power at about 2500 rpm.   The car starts fine and runs fine at low rpm but as soon as I get it up to 2500 rpm it chokes out.  If I take my foot just slightly off the gas it is OK.  But if I try to go faster it does it again.  I had this problem last year already so this year I decided to remove the carbs and clean them and set them back up. Also lapped the valves and adjusted. None of which fixed the problem.

I was wondering if it could be the fuel pump or coil. Please let me know what you think.

Heinz Kettler


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    • University Motors
Re: Loss of Power
« Reply #1 on: February 14, 2021, 01:08:36 PM »
here are many problems you could be having, but from here, Id put my money on a faulty fuel supply.  Remove the fuel feed to the carb, put it into a can or bottle, turn on the key, and expect to pump ONE pint per minute.  If the line just dribbles, then there is a problem with the fuel filter, fuel pump, hoses, or the tank.

If the fuel supply is just fine, then I would look at the point gap next.  Ensure the points are opening 0.015.

After that, back to the carbs as the floats in the HIFs can be installed left to right and that results in low fuel in the carb float bowls.

Hope some of this helps!
John Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids MI 49506-2410
Cell  616 307 6737
John H Twist
University Motors Online
100 East Beltline Avenue SE
Grand Rapids, MI  49506


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  • chfwrench
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  • MG information: '73 red B roadster
Re: Loss of Power
« Reply #2 on: February 19, 2021, 08:35:44 AM »
Hi Heinz,

Adding to John's comments, another very common issue with these cars is the advance system of the distributor.  Failure of the advance system vacuum pot causes much the same loss of power issues as you are seeing under acceleration. 

There's a mechanical advance system as well that can get rusty and stick or the springs become weak or break.  Generally if in good shape, that system could work up to a certain point, but sudden changes, like hard acceleration, or at higher RPM it would not and the engine would 'bog down' and sputter.

Your B should have the 45D4 Lucas distributor, which parts are still available for and a complete new replacement unit is still made and available from Moss or other catalogs.

Safety Fast!

Art Isaacs
AMGBA Tech Staff


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