1997 GTI wont a run or idle.

[Cain64]

I have a 1997 GTI and i just rebuilt the carburator, and am still getting the same problem, when first put in the water runs great then after about an hour it dies by it self and or wont restart. If i take it out of the water and let it sit for a minute it starts and runs fine. What could be the problem, i replaced the fuel line the fuel filter rebuilt the carb, and still the same problem.