bang and black smoke

[den]

Getting a 1967 series one 4.2 e type that I have inherited running again. It's been started up and left running a few times successfully but the last time there was a loud bang and lots of black smoke from the exhaust. This happened again in quick succession and then switched off quickly fearing the worst. Any ideas what could have caused this?
Thank you

[Jack the lad]

Hi Den,
One or more cylinders not firing putting unburnt petrol into the exhaust system, this "bomb" is then ignited by the exhaust from one of the cylinders that is firing. The black smoke is carbon deposited in the exhaust many years ago being liberated. Provided that you have not damaged the exhaust system, when you find the misfire everything should be OK. cheers John.

[den]

Thanks John.
So do you think it would be ok to start up again and take out for a quick run? I know nothing about cars!
Den

[Jack the lad]

Hi Den,
NO, not without sorting out the mis-fire. You could do a lot of damage to the engine/gearbox and you really don't want to risk that. If it has been stood more than 12 months you need to drain the tank, fuel lines, fuel filter and carbs refreshing with some new petrol. If the engine runs sweet after this you could give it a gentle run out but really would be better if you had it re-commissioned by a mechanic. get him/her to change plugs and points, oil and filter as a minimum. Where are you situated? many on here are most helpful at "mates rates" for this sort of problem, cheers John.

[den]

Thanks John for your help. . Its been stood for a year. The tank was replaced at beginning of this year and has been started up a few times since. Need to get it roadworthy to sell, based near Reading.

[Jack the lad]

If the tank was replaced at the beginning of this year the petrol should be OK, but did they drain the old tank and put the old petrol back in. The fact that you were charged for the new petrol does not mean that you received it. Also the old petrol would have still been in the fuel lines, filter and carb bowls.
Another theory could be that your regular starting it up could have caused an amount of petrol to be held in the inlet manifolds ready to be sent to the exhaust unburnt ready for the explosion the next time it is started.

[lowact]

Was anything done to the car between when it ran ok and when it didn't, like, could the distributor have been removed and replaced in the wrong position, or could the spark plug leads have been disconnected and reconnected to the wrong plugs?

[den]

Just tank replacement, and got it starting up again after that. Drove up and down lawn (Small lawn!) a few times just to move it and that was ok,and put it back in the garage for a couple of weeks.
Appreciate your help.

[malcolm]

I must say, where there are electrical (potentially) issues, I'm a bit of a believer in changing everything (leads, coil, plugs, rotor arm, dizzie cap, etc) with new, and keeping the old as spares. It doesn't actaually cost that much. You can then replace parts a bit at a time until you find the culprit and chuck it away. Of course it may not be electrical! But hey ho...

[DWW]

First thing I would do in such a case is check all the spark plugs to determine whether there is a misfiring by seeing wetness on any of the cylinders.

[eddiecross]

Just guessing but I would check for an intermittent stuck exhaust valve.
I would pull off both rocker covers and spin the engine with the coil disconnected (pull the plugs to make it easier on the starter)

Get someone to spin the engine while you check for consistant oil feed to each valve and all valves opening and closing with no delay.

Good luck
Eddie