Info needed

[gilly]

the bulb does not stay hard after the engine runs a little. if the engine continues to run while you pump the bulb, your problem is a bad fuel pump.

[kydog]

I'm just guess but if the fuel line is quite few year's old it could be getting dry rotten and bleeding seeping air. Just a thought.
Dog

[bcnitro]

If you have a main tank and a reserve tank your valve to switch tanks could be leaking by too. A buddy of mine had that problem. Gilly is probably right about the fuel pump though. I have had the same symptoms and the fuel pump solved my problem.