Wear and Tear. One common reason for a primer bulb collapse is deterioration due to old age. The fuel the primer pulls into the combustion chamber is a volatile organic compound -- a solvent. Sep 08, 2011 · The primer bulb is suppose to fill the carburetor with fuel by sucking it through it through the fuel line (the one with the filter on it). The other line is just to pump the fuel back into the tank. Check this web site and look at the illustrations. One shows the primer bulb pushed and the red is fuel, the blue air. May 29, 2011 · The last bulb bled off in app.3 hrs. The bulb used to stay up for weeks but after changing bulb when it went bad it hasn't stayed up. Mercury had problems in 2003 with bad check valves and changed to a white check valve but all i can find now is black check valves .