When it's hot, try bringing it up on compression, ignition on, kick it. See if that works. Alternatively try wide open throttle. Probably doesn't need the tickler when it's hot and full of fuel. I know mine didn't.
It's also possible that the float level is too high or the needle/seats aren't sealing too well and that the added fuel pressure (there's a actually a word for this, I think) is causing some overflow/excessive richness.
One assumes the engine would be hot because usually one rides to a gas station, but he could of course fill the tank from a can at home.
For some reason, my mind went the other direction. Excessive rich mixture will surely be a problem cold, but in a hot combustion chamber (Assuming it is warmed up of course) is less of a problem in my mind. Seems like lean is the issue to me. I wonder what the temp is when it IS running. Hmm. Ahh the glorious job of chasing gremlins. We all say we hate it, but yet we stay and endure the torture.
Yes it's when it's hot, as I ride it to the gas station. It runs rich, as before it used to die on me at the lights, so I tweaked the carb to get the revs up a bit at idle.
I think 59 might have it. My plugs always look dry & darkish, coked I guess because of running it too rich....
Double check the gas cap vent, loosen the cap before starting and see if it makes a difference. Also, do you have a thick gasket between the carb and manifold? Maybe the fuel is boiling from the heat transfer?
This sounds like the type of problem I'd run in to...........good luck!
Have someone watch pipes when it does finally fire up, shot of black smoke your tracking a to rich gremlin. Could also pay to take out plug and see how strong your spark is when kicked. Ignition gremlins are a bitch.