Warming plugs is some thing we used to do to the race bike in winter.
Normally I would not do it however when I am having troubles getting an engine to start I some times resort to it.
Now days with the garbage supplied as fuel ( which is not petrol ) and with plug insulators are no longer glazed, in very cold weather fuel vapour condenses on the plug.
At combustion pressures this deposit is highly conductive so you get no spark, it just tracks down the side of the electrode.
This is why you hear a lot of people complaining that a plug went bad right out of the box.
Warming the plug till it is just too hot to hold in your bare hand will stop this happening so at least you can start the engine and make any adjustments that may be necessary.
Modern fuel is nothing like petrol and it only has a small amount of volatiles in it that vapourise at low temperatures to allow an engine fitted with a carb to start.
Once this fraction has evaporated out of the fuel there is no way it will fire in a cold carbed engine and my first guess is you fuel has lost this part.
This is why starter fluid sales have gone through the roof.
When we had real petrol there was only 1 brand sold locally and all the cans were covered in dust as it was only used with really old diesel engines.
Now there is 12 different brands in the car parts shops, they take up a full shelf and it is even sold at supermarkets.
Now there could be a host of things that is stopping the engine from firing, but the bad fuel / bad plug is the most common and easiest one to eliminate.
It has happened to me so many times it is not funny, I start an engine, turn around to pick up the tuning tools and the instant they make contact with the carb the engine dies then refuses to start untill I change the plug which was usually brand new.
The old tricks we used in our youth like tipping some fuel into the plug hole or down the carb throat just don't cut it with modern fuel which is formulated specifically for modern fuel injected cars and not anything fitted with a carb.
As for your specific problem
Your motor started but failed to get up to the full operating temperature required to vapourise the fuel.
It just stopped & now wont start.
There were no pops , bangs, backfires, missing, it just stopped while sitting there , probably at idle speed .
You had not moved it, engaged any thing it was just sitting there then stopped.
So the no 1 suspect would be water in the carb & fouled plug
The no 2 suspect would be bad fuel & fouled plug
