That's irritating, putting it mildly.

I would still be looking for electrical causes because you say it fires up again straight away, so fuel problems are less likely. How about:-

Kill cord wiring and switch if fitted.

Ignition switch, particularly if it's like the car type that switches the ignition on then a turn further to engage the starter, that would explain how it's managing to fire up straight away because you are effectively re making the contact.

Good luck, hope you find the cause soon before it becomes one of these frustrating missions, systematically changing every part to trace the fault.

Many thanks. Yes, kill switch checked and bypassed just in case.

Good idea on the ignition switch. It is as you describe. I’ll take a look, identify it and replace.

Kind regards

R

Keep going, please recheck that you have a spark when it won’t start, it’s possible that there’s still something in the electrics. Also, I’ve had a magnetic electronic ignition fail quite quickly and give the symptoms you have.
If you have a spark then go for fuel pump diaphragm, blocked or dirty tank, pipe, carb float chambers jets etc.

Many thanks.

I fitted the electronic ignition as a result of the cutting out, so it shouldn’t be that unless it is an extraordinary coincidence.

Unfortunately the cutting out is instantaneous and when trying to restart, it restarts immediately so there is no opportunity to test for lack of spark.

I have ordered a new ignition switch as the terminals look as though they have been very hot at some point.

I will indeed check all of the fuel system... the fuel pump is also recently changed and is solid state.

I’ll keep going....

R

There is no good reason for the switch to be hot unless the contacts are dirty which would have complex results, including be8ng intermittent.
Yes, it could be that the switch is bad. An easy test is to have a 12 v filament bulb across the coil. It should light when the points are closed and be a bit dimmer when running.
If the bulb does not light you can back track through the system, for example, coil positive and earth should light the bulb when the ignition is on. If it’s in the you have power to the coil, if it’s off then back through the ignition circuit.
If you 12v at the coil when the ignition is on but if the bulb does not light when across the coil then it’s the points/ electronic ignition.
There’s a very good reason to use a filament bulb in that it draws current and hence will show up a bad connection. I’ve seen at least one case where a voltmeter showed 12 volts when the load was off but a bad connection (fuse) upstream meant that the power disappeared under load.

When it restarts does it run OK? A good friend had an Albatross 100E single SU that would ice up the carbs if run flat out for long. Although it didn't cut instantly to be fair, just started slowing down, ease the throttle & it s away again.

I was going to suggest coil overheat but if you say it starts again instantly it probably wont be that. Just to be sure though try disconnecting the dynamo/alternator & trying it. I know of two instances (1 boat (dynamo) & one car (alternator)) where coil cutting out was caused by overcharging, disconnecting whatever charges your battery will be an instant yey or ney.