Fuel to carb when cold problem?

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I have a 85 B2000 SE5. Runs fine normally but let the outside temp drop and the fuel pump stops running. The fuel pump is fine, works great when jumped out. plus I just replaced it a few weeks ago. Fuel filter is good. It'll crank and burn the gas in the carb then goes dead. The float in the glass window is bottomed out and no gas in the window?? As soon as the temp warms, it'll crank and run fine again?? It's driving me crazy! Truck sat for years, it only has like 51000 miles on it. I've had it about a year. This problem just started this winter. Any help would be greatly appreciated. Thanks.