You really take spare primer bulbs into the field? I modified the FS250 so that I wouldn't have to.
With the pole saw I described, it wasn't the bulb that was the issue. The primer was integral to the carb, and it was the check valves that were shot (granted, the owner had left fuel in the tank for so long the fuel lines were gone, and the filter had started to corrode). With the open check valve on the carb side, the saw would not run. I had to drill the valve out of the carb, and tap the hole for a set screw or buy a new carb.