If you are ABSOLUTELY, TOTALLY, convinced it is the carb.
Its an ignition fault ...............
However ....
Make absolutely sure you are getting fuel-flow to the carb -
I slacken the nut holding float-chamber onto carb-body, turn the fuel on and catch at least a margarine-container full (goes between carb and mag on a Norton) of petrol - it should fill rapidly and test the entire fuel flow path.
Before pouring petrol back in tank - have look in the petrol to see if any water in it (a problem for me, trailering bike around in the rain)
A 'quick' magneto 'bodge' is a Sparkrite capacitor that fits under the points - no need to remove mag/armature to do recommended 'snip' job - if the capacitor's the problem it will improve things and more importantly point you in right direction.
I went to the shed tonight two kicks with decomp lever in, retard about 1/4 advanced throttle open, picked up comp stroke and away she went. Left it idling for five minutes turned it off, tried starting about six kicks thought I would try wide open throttle second kick away she went. Repeated idle warm up and it started again. Need to go for a ride and get hot so I can try then. Only thing I have done is retension the head and replaced the plug lead although the old one looked good I noticed last night once it got hot it felt very limp. So I will have to wait until tomorrow night to try again. Any thoughts as to why the wide open throttle works but I don't need it when cold
Cheers
Roger
The wide open throttle allows both more air and more fuel in, when the engine is hot, the requirement for more cold air and is greater, so the extra 'fresh' oxygen and fuel, make even the smallest spark count.
