If it only runs on 'choke' then I would be looking to investigating the petrol system;
photograph the parts before and as you remove them
remove and drain the tank to inspect the tap filter;
thoroughly clean any debris from the wiring and frame around the carb before removing it
check the flexible supply pipe between tank and carb for partial blockage - I actually found a piece of wood in a pipe once
inspect the carb to cylinder head sealing, the flexible carb to head rubber and carb to air box pipe and security too
remove the carb for a full strip down and clean, take care to note the position of any tiny washers around the needle - an egg box makes a good safe storage for dismantled parts
inspect for dirt or water in the jet system
inspect the diaphragm very closely for tiny splits
if possible immerse the carb in a sonic cleaner and blow out the airways with carb spray and/or compressed air pressure
while your doing all of this clean and re-oil the air filter element, check the drain and clean it too
as to the electrics;
check the plug cap to plug lead as corrosion can occur around the screw that enters the cable, I bought a new angled waterproof cap off eBay - the green spark plug company - but check the terminal type
as suggested before perhaps fit an NGK iridium option spark plug
TTFN
Hugh.