Try this... take a squirt bottle and spray a little bit of gasoline on your air filter. Hold the carbs wide-open and kick it over. If it fires up, you're probably not getting enough gas & I'd check your choke circuit. Maybe disassemble the carbs and give them a good cleaning. Are you running the stock head? Maybe a cool head with some aftermarket domes with a better squish angle could build a little more heat in the dome during compression and help it start when cold. Check all the normal stuff, choke tube, clean carbs, maybe try the next size up pilot jet and see how it likes it....
- Jared