Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Engine cutting out

Rob, replace the HT leads next, I've also had dodgy HT plug caps cause misfire at revs

Burgundymog Thanks for the suggestion - are there any tell tale signs on the plug that would indicate it was breaking down , residue or coloring ?

Rob if you stop the car when it misfires and remove the plugs you will probably find one that is a different colour and likely wet.

If you have access to one of those IR laser thermometers (cheap as chips these days) a misfiring cylinder may show up as a cooler exhaust header ... Morgan's having separate and accessible stubs out of each cylinder should help with this.

K

Do the cheap and simple checks first.
1974 car so age related deterioration might be a cause.
Are you getting fuel through ok?
How old are the plugs and leads?
Any air getting sucked into the fuel lines/carb?
The short run after cooling down then recurring problem might be heat related. As a component warms up it can expand causing air to leak in, failing electrical components change when warmer etc. Check the vacuum system that feeds to the distributor. Warming the pipes can cause leaks in weak/ deteriorating pipes.
I’ve had misfiring due to failing plug leads years ago. New leads sorted it. A 17 year old car with what looked like original leads. Carb, coil, distributor/ condenser all checked ok.

With engine running in mis-firing mode, simply remove and replace one plug lead at a time. Each one that is healthy will make the engine run worse when removed. The faulty one will make no difference to the missing sound.
You may want to don a pair of rubber gloves to avoid any shocks in case of poor insulation.
This test would simply tell you that the fault is in either that particular plug or plug lead and rules out things like condenser, points, coil or fuelling issues, etc.