Vapor Lock

[cleandan]

BlakeC, the problem you describe is heat soak induced vapor lock. Because this does not happen while driving I am assuming the heat soak, after engine shut off, is evaporating the fuel from your fuel bowls and maybe even the lines a little, along with boiling what gas is left in the carb. This happens because of the low vapor pressures of modern fuel (mixed for higer fuel pressures) There is not much you can do about this other than make certain everything is up to par. Timing is right on, fuel pressure is as high as your carb will take (about 8 psi max, 10 psi in some cases), float levels are correct and seats are tight, insulate and isolate the incoming fuel line as much as possible as well as running as small a line as your motor will take (no fuel return system), or go to a return style system, (a better idea) and try to distance the carb from the heat source...tough to do when the heat source is the motor itself. The under carb spacer works pretty good at heat isolation from the manifold, but does not fix heat soak from hot underhood air simply heating everything under the hood. The 1/4" spacer is just as effective as the 2" spacer at heat isolation with wood being the best isolator, then phenolic, then plastic, then aluminum (I like the phenolic) The "turkey pan" will deflect some radiant heat, as well as allow cooler air from the hood scoop to cool the carb body itself and this will make detrimental heat soak take longer to cause problems, but it will not make heat soak go away. Nothing can make heat soak go away except for removing the heat. One way to tell if this is really the issue is to drive until you have everything really good and warm (go for an hour long cruise on a warm day) Then stop for lunch somewhere and after about 10 minutes have passed, remove the aircleaner and pump the throttle while looking at the accelerator pump nozzle discharge. If there is no gas, or spurty, airy gas, you have found the issue. If you have clear, full spray, then look elsewhere for this hard start problem. Good luck.