I have owned a 1200AES and the starter O-ring can be a PITA. It sounds like yours may be holding on too long or not getting the engine up to speed. The ECU unit does not feature a prime as already been stated. I usually made sure there was fuel in the line as close as possible to the engine. WIth a full battery cahrge, a good O-ring, plenty of gas, and a good glow plug you should get a failry quick ignition and ramp up with this engine. My tailcone always glowed if the start up was even a little wet, but as soon as the engine ramps up it, it would stabilize and would be OK.
TOmmy