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Classic Car Service
Classic Car Service, Dealership Svc. Mgr.
Category: Car
Satisfied Customers: 4605
Experience:  Over 30 years experience in the automotive field
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Our MGB: when motor is running, all lights flicker and rev

Customer Question

Our MGB : when motor is running, all lights flicker and rev counter bounces. Wondering what is going on. Slight miss in the motor occasionally. Can you help.
Submitted: 8 months ago.
Category: Car
Customer: replied 8 months ago.
Ignition light flickers as well
Expert:  John Vieira replied 8 months ago.

Hi I will try and help you tonight

Customer: replied 8 months ago.
Have not heard anything from you yet?
Expert:  Classic Car Service replied 8 months ago.

Hello. Different expert here. I see that you have been waiting for assistance. Please allow me to add some input. On these cars, the main cause of the dash lights flickering is eithe a loose alternator belt of a faulty alternator (assuming your misfire is not causing the RPM to drop substantially).

Engine misfires on these cars are common. There are quite a few vacuum lines under the bonnet that can become weakened with age, and develop pin hole vacuum leaks. It does not take much of a vacuum leak to compromise your idle quality. Assuming the engine is in a proper state of tune (good/new plugs, cap wires, rotor, etc), If this car was in my shop I would be looking at each and every vacuum line in the engine compartment for cracks, brittleness, softness, poor fit, etc. I have worked on a lot of the MG product over the years (I own an older Lotus), my experience with these issues leads me to believe your major concern is vacuum issues. It is also possible that you have a vacuum leak at the intake manifold gasket or under the carb.

If you have any questions, please feel free to reply; I will be very glad to help you further.

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