RE: OS 70 Ultimate w/pump
The problem is that fuel in the pump/regulator system dries out and you have to turn the engine over a bit to get fuel back into the system. The best way to get fuel back in is to open the carburetor to full, choke it with a finger, and turn the propeller over by hand in the normal forward direction. This will eventually draw fuel into the pump and carb system, and then up, into the cylinder. When you can hear fuel spitting out of the exhaust port, remove your finger from the carb intake and briskly flip the propeller forward through compression several times. Now retard the throttle to just above idle, attach the glow plug battery, and start the engine. The pump needs to be primed, once it's become dry of fuel.