I know it should work, probably something minor. With the cowl off, I primed the motor, and watched as the fuel gets sucked back into the tank. That was with both tanks. I think it may have to do with the exhaust port being below the level of the tank, which wasn't the case when I mounted the motor upright. I can also get the old motor to start in 3 or 4 flips, once I reset the needle valve, and leaned the idle mix back to normal. In the old plane, the carb is a full 1/2" higher than the tank itself, along with the exhaust pressure port. On the Rocket, the carb is in line with the center of the tank, the exhaust pressure port is below the tank. This was why came up with the idea of a check valve on both lines.