MGB Register Forum

Dave,
Given that you appear to have sparking at the plugs under cranking - worth checking fuel supply side. If original type fuel pump you should get between 1 & 2 pints a minute, if you pull off the fuel pipe attached to the front carb & put it into a container. I've had a gummed up fuel filter in the past that caused fuel starvation which can stop the "old type" fuel pump ticking etc. Is the pump working? Poor electrical connection to the pump?
Cheers,
Charles

Well,this has turned into a marathon. Plenty of fuel at the carbs. Had to remake a couple crimp connectors at coil and to the distributor. Checked the points and timing. Called in no1 son who condemned the spark at plugs as hopeless. Reddish colour. He suggests trying coil off the Cortina, which we will do tomorrow. I've had enough for 1 day. Funny, the car was running fine before the temporary layup!

Dave,

Just remember that as long as your car's wiring hasn't been altered to eliminate the ballast wiring when the ignition is in the run position , then you should have a ballasted coil. If a non ballasted coil is used,(designed for running at 12V) then in the crank position the "spark" & voltage will be reduced by the drain of the starter motor & once running the "spark" will be reduced by the ballast which isn't sufficient/is poor for a 12V coil (Made worse by a poor battery & cold conditions). A ballasted coil, which is what was fitted as standard for the 1974 1/2 - 80 cars was designed for running in the 6V region via the ballasted feed. This was boosted on cranking via the non ballasted feed from the back of the solenoid on the starter motor to 12v to temporarily create a better spark on starting particularly in winter conditions.
I assume your distributor cap & rotor arm, points wiring, etc. are in good condition & leads in correct firing order of 1342 ?

Cheers,

Charles

Don't use the Cortina coil as it's 12 volts. Your MG is 6 volts as Charles has already said. This problem cropped up a few months ago on this forum so it might be worth finding it. I remember it went on for a good few pages but I don't remember the outcome.
To me, it's an unnecessarily complicated set up. When owners fit a new starter motor they should make sure the new one has the terminal for the 12v coil supply fitted, especially if replacing with ehigh torque version.
Not all have that terminal.

My Cortina runs a ballasted coil ( I Think ). I 'll make sure first.

A direct 12v to the coil, and she started instantly. I could have knocked a connector off the solenoid when replacing the plastic cover, but I'm not even going to look. Could be the ignition relay I suppose. I'm going all 12v now. Fed up with blooming ballasts etc.

Dave,
A result then!
If you are going to dispense with the ballast feed for running, then I'm sure you know you will need to fit a 12V coil (i.e. non ballasted) otherwise the coil will burn out in a relatively short time.I'm not sure if your original wiring has been altered either by a PO or yourself & don't know what coil is actually on the csr!
Cheers, Charles

Hi Dave
I agree with Vic, BL seems to have made a bit of a meal of this. You could change the starter relay for one with an extra output terminal 87b. Connect the Red/White wire to 87 run a new white/LG from pin 87b to the coil (or find the existing wire in the loom that goes down to the starter solenoid) This way you don’t need to worry about any further messing with “that” cover.
Mike Barclay

Michael,

If i understand your suggestion correctly, as the starter relay is only energised under cranking & therefore with original wiring is isolated thereafter - if you then replace it with an additional terminal 87b that is connected directly to the coil via a new W/LG lead won't that then become live all the time (& hence feed the starter solenoid etc.)when the engine is running via the ignition relay etc. unless a diode is put in that new W/LG lead?
Is the replacement starter relay's additional terminal 87b isolated from 87? If it is , how robust is that isolation electrically? I am aware that you can buy relays that have built in diodes & read some where that modern replacements are recommended to be used with these to prevent running on , current feed back etc. The original types as fitted to our cars have much more robust internals that have better isolation without the need for internal diodes.

Cheers,
Charles

Hi Charles
Please see the attached picture. For some reason this did not go through on my original reply. This relay has 2 separate output terminals (87 and 87b.) They are electrically separated when the relay is not energized so the Red/white wire and White/LG wires would not be connected together. This will then do the same job as the starter solenoid but avoid having to mess around under the car gaining access to the starter motor. The equivalent of the White /LG wire could be a new wire or it could be traced back in the loom from the coil end as the coil and Starter relay are in close proximity.
The relay is readily available from most of the car electrical suppliers and see no reason for the contact to be any less insulated than any other relay. .
The built in Diode's are usually across the relay coil. This is to prevent the Back EMF (Electro motive force) caused by inductive loads. Basically its a the collapse of the field current creating a large reverse voltages. The effect isput to good use as itis how a standard points ignition system works. An example of its effects is the coil in the SU petrol pump why the contacts burn out )
Hope that helps.
Best regards
Mike Barclay