Hard starting when hot, or cold

I used to have a problem where the bike would start up fairly easily, but would cut out on me after about 5 minutes of riding. Now my bike runs well, but has a hard time starting when it is 'cold' and 'hot'. However, when I get it started and ride it for a while, then turn it off and let it sit for a 1/2 hour or so, it starts right up. Any clues?
The carbs were just taken apart and put back together for the nth time. Petcock and fuel lines are good.

Maybe change the plugs & clean the ignition contacts in the points or electronic ignition.

Mine did it too & this cured it for some reason, also cut the plug wires back about 1/2" to get into clean metal, I used dialectric grease on the wire ends to avoid more corrosion in the future.