[LBJ]

I tested my old locking (STANT brand) gas cap by testing it with a vacuum pump to see if it allowed air to come into the rubber diaphragm/valve. You can "suck" on it and see real fast if that is working. Or, remove the old gas cap, get some real heavy duct tape and seal off the fuel nozzle opening and punch a small vent hole in it and then drive. Try not to make too many fast corners or you'll get spillage. But, you will be able to see if it runs or not. Mine took about 10 minutes to build up enough vacuum to kill the gas flow, with an almost full tank, with the old gas cap. Or, just buy a new gas cap and test it out. Gas caps aren't too costly and won't hurt to replace it anyway. That's the least trouble and most likely source of the problem. I start with the easiest solutions first, usually, but when it happened to me, I never thought of the gas cap being faulty. ha. Wasted LOTS of time and money on a new fuel pump, gas filters, fuel line, and a carb kit (never installed it though) until a friend suggested that fix.