Back in the 1960s when I had bikes that didn't like the cold it was possible to buy a spray can of ether, which one sprayed into the air intake. It certainly worked, but I'm not sure it was good for the engine.

Another trick was to take the plugs out and heat them up to "hot" in the kitchen oven before putting them back and starting the engine.

Peter,
66, 2016 Porsche Boxster S
No longer driving Tarka, the 2014 Plus 8...