Took my new used boat out Sunday and the gas bulb collapsed and the boat wouldnt start. we took it loose and then put it back on and it was ok. what should I replace first? just the bulb assembly?

Check the vent on gas tank and the fuel pickup.

thx

Some of the older fuel hose is not compatible with ethanol and can delaminate internally causing a blockage. I wold replace the bulb and fuel line since you are having the bulb problem.
Make sure the fuel line isn't pinched anywhere. I had the same problem with my new Seaark and the fuel tank had slid over against the fuel line and was pinching it closed.

Disconnect fuel line at motor and depress the detent in the fitting. if it stays collapsed its your fuel line is blocked usually from ethanol breaking down the fuel lines. Be sure the lines don't have that cheap plastic liner inside them as they only last a few hrs til it happens again.

Check your ant-siphon valve, its probley stuck and needs replacing