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MG MGB Technical - MG won't start

I have a 76 MGB and am having problems starting it. It had a new ignition switch and alternator put in and the battery is fully charged. Just got it back from the shop and it started just fine 2 days ago. I opened the hood and saw that a wire that goes between the carb and intake manifold came off - I reconnected. A red wire with an inline fuse that feeds off 4th fuse down on the left had no fuse in it but was connected by having the wires connected. I replaced the wire with another in-line fuse wire - is this wire for the ignition? it also is connected to another wire. I am a novice at MG's and would be open to any suggestions.
FJE Frank

Firstly the ignition is not fused in factory wiring.

The red wire you mention sounds like it will be picking permanent 12v up from the brown (if at the front) or the purple (if at the rear, and which is fused anyway). It is a PO wire and could go anywhere.

On a US 76 there should be a green wire from the harness feeding the Zenith carb inlet manifold heater. No wire from the carb to the inlet manifold as such, as you sure that isn't a tube or pipe?

First thing to do with a non-starter is to be precise about what you mean by 'not starting'. Is it cranking over with the key but not firing? Or not even cranking over? I'll assume the former.

Clip a timing light onto the coil lead and each plug lead and watch the light while cranking - it should be flashing.

If it isn't flashing on the coil lead it could be an ignition LT problem, you need a voltmeter to check the voltages on the coil +ve and -ve. A 76 should have a ballasted (resistive) feed to the coil, and this means you should see the voltage varying between 12v and 6v on the coil +ve, and between 12v and 0v on the coil -ve as you turn the engine. Cranking will probably turn the engine too fast to see these changes, especially with most digital meters, so you may have to turn the crank with a 1 15/16" socket or put it into 4th and nudge it along. If you do either of these *take the coil lead out of the coil beforehand* or if the engine suddenly catches it could do you an injury. If you see those voltages then it sounds like a faulty coil. If not then you need to investigate the 12v feed to the coil, and the points or electronic trigger depending on what distributor you have.

If it flashes on the coil lead but not the plug leads, or not all of them. then it sounds like the distributor cap and/or rotor breaking down, replace both.

If it flashes on all leads regularly and consistently take the opportunity to check the timing while conected to No.1 lead, it should be showing about 10 degrees BTDC.

If all that is OK it could be fuel, take the plugs out and sniff/inspect them. After cranking for a short while without starting they should smell strongly of fuel. If they are wet with fuel it is flooded, which *will* happen after a lot of cranking with the choke out on a non-starter, but you should be able to smell this anyway. In either of these cases you have sparks and fuel so the engine should start, I'd double-check the plug lead order and timing.

But if they are dry with no fuel smell fuel isn't getting through. After leaving the ignition off for several minutes, ideally overnight, can you hear the pump tick a few times when you turn on the ignition? If not it sounds like the pump or the voltage feed to it is faulty. But if it ticks and the plugs were dry it isn't getting through the carb, so check the float chamber.
Paul Hunt 2

Thanks Paul for your input, I was able to get the car started. Yes, you are right, the wire I mentioned was a green wire from the harness to the carb inlet manifold. This is the one I hooked up. Just for the record, how I got it to start I do not know. I believe I must have either a short somewhere or a contact is not secure.

The car was cranking but not firing. I do hear the clicks from the fuel pump and I do smell gas. I will continue to monitor. Hopefully it is fixed.
FJE Frank

OK. If it cuts out on the road, then before you dip the clutch or switch off, and with the forward momentum of the car still spinning the engine, have a look at the tach and the ignition warning light.

If the tach has dropped to zero it is an ignition LT problem, if not an HT or fuel. If additionally the warning light is on then the 12v supply to the ignition from the ignition switch has been lost. But of course if this is the case the light won't be on while cranking.
Paul Hunt 2

This thread was discussed between 06/10/2007 and 07/10/2007

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