You might have to try a couple of things but the first I'd try is giving it a shot of mixed gas in the carb & see what that does.Have you checked your spark to see if its nice & blue?Make sure no wires are grounding out.
If this is a problem for the first start of the day, go through all your fuel hose fittings/connections and carb screws and check for good seals and connections. Sounds like it is loosing its prime and then not primmming good when you go to start up. The longer it sits the harder it starts, ???