Essentially, mine would die right after first start up cold.Only way to get it running would be to rev the motor in neutral for a split second and then after its perfectly fine, no issues from idle to wot. Or i could crank it for like ten seconds and it will stay running. If its still hot it starts up no problem. The diaphragm is a common problem in optimax motors, i inspected the fuel side, not air, high psi spring inside.