MG Car Repair: 77 mgb, webber carbs, ballast resistor

Question
hello. I recently purchased a 1977 mgb. It has been in wet storage for nine years. I flushed the fuel system rebuilt webber carbs new oil and filter removed spark plugs oiled cylender walls and cranked enine by hand. When I tried to check for spark I had none when cranking the engine except when I let off the key now and then I would get a spark from the coil wire. I should say the engine cranks very hard. Installed new battery. still cranks hard. starter checked ok but that was not under load. If the starter were bad. would that cause no spark?

Answer

MGB starter solenoid   Hi Brian.  Given that your MGB has a Weber carb, it may have other modifications, such as an electronic ignition conversion.  I am basing my reply on the assumption that it still has the original ignition setup.

A 1977 MGB has a ballasted ignition coil which is normally fed via a ballast resistor wire inside the wiring loom.  However, there is an extra small connection on the starter solenoid that bypasses the ballast resistor and powers the coil directly while the starter is operating.  From your description, I think this wire is not doing anything, so the engine only fires when you let go of the key.  This wire often gets damaged or it may have become disconnected.  It is very vulnerable on the bottom of the starter motor underneath the engine.  I have attached a photo of the solenoid.  The larger connector is for the actuator terminal.  The smaller connector is for the bypass wire.  

As a temporary measure, run a wire from the WHITE side of fuse #3 directly to the + terminal on the coil.  That should allow the engine to start.  Once the engine is running, disconnect the wire and it should continue to run without it.