For such starting problems, either install a 'purge valve' on the inlet side of the carb ... will 'force' fuel to completely 'fill' the carb's 'bowl chamber'; if the 'bowl chamber isnt completely filled with fuel you will not obtain the proper fuel/air ratio.... or simply remove the gas cap on the 'internal tank' and 'pressurize the tank' with your mouth for a few seconds. Usually after starting the small diaphragm pumps (rubber 'flap' valves, etc.) will be operating normally .... the problem is the 'starting'.For some reason, I have a really hard time starting it with the internal tank -- I thought the internal tank would be great because this motor sips gas, and most of the time I wouldn't need more than 1/2 gallon, but I haven't used it since the first few dys that I had the motor because of the starting problem. I think the problem may be because there is no way to prime it with the internal tamnk (there is no primer bulb), but I'm not sure.
I'd be curious to hear if anyone else has had this problem with an internal tohatsu tank.
If 'mouth pressure' on the tank remedies the difficult starting, then strongly consider to add a 'purge valve' to the carb .... do the mouth pressurization of the tank 'first' and if that 'works', then consider the purge valve. The 'mouth pressure' will help to remove any 'air bubbles' that were formed in the fuel line during long term 'shut down' and will help to fill the 'carb. bowl' chamber. Such 'purge valves' are usually found on RELIABLE top of the line chain saws, etc. such as Husquvarna, etc.
Also with hard starting, you can consider to use LARGER (inside diameter) hosing from the tank to the carb ... with larger connections to reduce the 'flow restrictions' that are presently restricting proper start-up fuel flow. Those fuel lines should be 'straight as possible' and without kinks and with minimum 'bends' to ensure proper fuel flow).