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MGB 1979 MGB with Weber carb

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T

TFR

Jedi Trainee
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Have a question... Guy I know brings his car over for me to investigate the cause of the car losing power on the high way. It doesn't pull well while accelerating or going up hills.

Checked the compression and it runs between 120 and 128 front to rear. Normal, so I understand is 125.

So I think it is the carb not tuned well. Does anyone know what jets are supposed to be in the carb.? I will post the exact model but I think it is a 40 DFAV. It could also be the accelerator pump...
 
I would check the following outside the carb first
*vacuum - if there is a leak it will affect timing
*timing - both at idle and increasing, doe s advance both vacuum and mechanical work properly
*fuel pump pressure - while at it check, replace or bypass for test the fuel filter
*proper spark at each cylinder - a MG will run on 2, just not very well

then look at carb
*is choke partially closed
*acceleration pump
*clogged jets or passages
*leaking gasket in carb assembly

Any of above may give off performance. If car ever worked fine I would not think jets are off. If car was relocated from sea leverl to Denver or reverse and symptons started then surely attempt to adjust jets , but a simple rebuild of the carb (is anything really simple) may reveal deteriorating rubber gaskets throughout due to today's alcohol content (or MTBE) in gas that this car was not designed for.
 
Was this a persistent problem or did it just recently occur? When was the Weber installed? Confirming that timing is correct and that the distributor is in excellent condition would be first steps. Are the valves set correctly? Is the fuel pump working correctly? Is there corrosion in the fuel tank clogging the filter? I think you'll find that the problem has little or nothing to do with the carb.
 
Guys,

Hope this doesn't cause you to stop helping but I am a TR guy so I don't have much experience with a MGB. However I do know engines and all of your suggestions are valid.

Could someone let me know the proper static timing. Also how much advance is normal. Is the fuel pressure supposed to be 3.5 #?

Thanks
 
Worked on the car most of yesterday and found that the ignition timing was way too far advanced. Not able to know the value but the timing mark on the lulley was at least 1.5 inches past the timing plate above the pulley. Retarded the timing back to 10 deg static and took it for a drive. It seemed to perform as it should.
Moving on to the rest of the issues on the car. Brakes and clutch...
 
Hello,

I have 76 MGB that was rebuilt in 2014. I purchase the car in 2018. I was told that it was in a garage for two years. When I purchased it. I have done the following:

  1. replaced a new weber dgv carb with standard jets.
  2. Replaced distributor with 45d electronic spark
  3. High performance coil
  4. New plugs and wires. Gapped correcly.
  5. New alternator.
  6. Set timing at 13 deg. Timing light.

In the beginning, the plugs would get fouled with soot but not oily. I did a compression check and it showed that it was within spec. So, I did the above changes but it did not stop the spark plugs from fouling. I was told after this that with rebuilds that the newer cams required the timing to be advanced. So, I advanced the timing to 22 deg and adjusted the carb and the fouling problem went away.

So, my question is that does this make since and by advancing the timing will this cause any long-term problem.

Also, I have also had a problem with run-on. I check the function of the run-on valve and it works when the engine is turned off. I have repiped the valve serval different ways and it does not help. The run-on has always been a problem.

Thank-you for any help.

JP
 
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