The problem is that the check valve in the bulb is very cheap and gravity dependent. If you want to connect both motors to the same fuel line, you need to make sure the bulbs are nearly vertical. The problem you have now is that it is just as easy for your big motor to suck fuel/air from the little motor instead of the gas tank. What I did is put in two stainless steel 1/3psi check valves in front of the engines so that I now have only one bulb to prime both engines. Works like a champ!