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MG MGB Technical - '74 MGB missing and sputtering.......

1974 MGB misses and stutters during acceleration while in gear and driving. It idles reasonably well and when I'm still and reving it up, it sounds fine does not miss. It's only when I accelerate in gear while driving. It sputters, misses and seems to lose power. I have new plugs, new wires (Beck & Arnley and they don't fit as snug on the distributor cap as I would like) and rotor and just changed the oil and filter. I've posted recently that I found a mouse next in one of the air filters and got into the carb. I've cleaned it out the best I could and installed a new air filter. Any thoughts would be appreciated. Thank you.

The first thing to check if it splutters on acceleration is the carb dampers, this is exactly what happens if there is insufficient oil. Unscrew the plastic cap, lift it up, press it back down again, and if you can feel the resistance of the oil before the car reaches the piston cover you have enough. If it goes straight back down you don't.

Other problems can be weak mixture, and ignition HT breakdown which I've had on two cars. The latter is easy to diagnose if you can reproduce it with your head under the bonnet by opening the throttle sharply and letting it go again. The objective isn't to rev the knackers off it as that will prove nothing, just see if it will start to pick up with a wide throttle. If you get the missfire then clip a timing light onto the coil lead and each plug lead in turn. If the coil lead remains consistent but one or more plug leads start firing intermittently with the problem then its probably the cap breaking down. If all four then probably the rotor. Rotors with a domed rivet inside the circle of the base are particularly prone to to this, use one with the rivet further out or with the original flattened rivet, see and click on 'Rotors'.

If the coil lead gets intermittent with the misfire then it could be the coil. If the tach gets erratic with the misfire then it is ignition LT, if not possibly condenser.
Paul Hunt

Paul...thank you for your response. The carb dampers are fine and have sufficient oil. I've gone under the bonnet and performed the throttle test and it sounds fine. I don't have a timing light, so I'll have to try new ignition wires, order a new distributor cap and rotor and see what happens. If those don't solve it then I'll have to order a new coil. What do ignition "HT" and ignition "LT" stand for? Thanks again for your response.


HT is high tension (high voltage like the big plug/coil wires and cap). LT is low tension (the 12 volt feed to the coil and distributor).

C R Huff

This thread was discussed on 08/08/2009

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