I have a 15hp Force motor that will start and will run as long as the warm-up lever is out. As soon as I push the lever in the motor will die. I can also keep it running by pushing the primer bulb when it starts to die. One thing I have notice is that the promer bulb for the tank will not stay frim. could this be my problem or ami I loosing the air pressure in the motor? The motor is about 10years old and has only been used a couple of times.