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MG MGB Technical - 1969 MGB GT - Turning over but not starting

Hi all,

I've got a 1969 MGB GT. Just replaced the head due to a crack. Now completed the rebuild and it's turning over OK but not firing. Have replaced coil, condenser etc and last night even tried cooking the plugs on my gas hob. just have a flat battery as well. Interestingly when I conect up my starter-charger the reading on the charger drops into the red and the ignition continues to toil - however when joumed from a running car it turns over quite well but there just is not a sign of it catching.

Fuel is getting to the carbs (twin SU) - so its not that. Any advice greatly recieved.



Was it running before removing the head? What did you disturb in changing the head?

Best is to start at the begining and remove HT lead from the coil at the distributor cap. Hold near an earth with insulated pliers and have some one turn over engine to check for spark. If OK then plug back in and check if spark at plugs by removing one plug and holding near the block. If spark then check timing in case you have fitted leads to wrong plugs or timing is moved. If no spark with coil lead check how points are fitted, I once put wire on wrong side of insulated washer - no spark.

Good luck

G Burrow

As the head has been off etc. it's back to basics.

First clip a timing light onto each plug lead and see if you are getting any flashing when cranking.

If not, then work through the ignition system checking for 12v on the coil +ve, and 12v switching on and off as the engine is rotated i.e. the plugs open and close.

If so it is either plug lead connection, timing, plugs, or fuel. Remember the firing order is 1 3 4 2 *anti*-clockwise, and make sure 1 is connected to the plug which is at TDC on its *compression* stroke. You can do this by removing the valve cover and turning the engine until No.1 piston is rising with both valves closed. Then look at where the rotor is pointing, and connect that lead to No. 1 plug. Alternatively if you remove No.1 plug and tuern the engine, when No.1 is on its compression stroke it will blow your thumb off (figuratively, not literally) the plug hole, stop when the piston is at the top of its stroke and check the distributor as before. Make sure the static timing is set to about 10 degrees BTDC.

If all that is correct, and the plugs are good, remove 1 and 4 after cranking for a while. There should be a strong fuel smell. If they are soaking wet they are flooded, but you should be able to smell that in the exhaust anyway. In which case crank with the choke pushed home and the throttle fully open and it should fire. If there is no fuel smell no fuel is getting through. Did the fuel pump chatter when you first switched on the ignition? Remove a fuel pipe from a carb and direct it into a container and make sure the pump chatters and delivers fuel with the ignition on. If that's OK remove the float chamber lids and there should be fuel inside, if not the float valves are probably stuck closed.

Correct all of those, and it *should* run.
Paul Hunt 2

I had the same problem when fitting an unleaded head. You need compression as well as a combustable charge and ignition. I was sure I had set the valve clearances accurately, but a compression test showed low compression on all cylinders. I carefully reset the valves and it fired up first time.
Phil Barton

This thread was discussed between 29/08/2007 and 31/08/2007

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