Okay before I shoot my truck I'd like to ask the experts here about this problem. In the early morning my truck will start perfectly and runs fine. I'll drive it to work and park only to come out at lunch and have it turn over but not fire. I live here in Boise, ID so the afternoon temps can hit 100 or above. I'll spray starting fluid down the carb but it never catches. My truck is a '85 Blazer w/305 vin H and q-jet carb. I've replaced the battery, dist. cap, rotor, ign. module, plugs and wires, and fuel filter but so far but nothing's changed. I've got spark and fuel delivery when this happens so now I'm completely lost. I was suspecting the mechanical fuel pump since it's factory original on a truck with 142,000 miles and never had a rebuild but I can't see why this would cause the problem. Any help is greatly appreciated, thanks.