Quote:
Originally Posted by Kenth
If this would be true, the inlet valves would be located at bottom of the float bowl.
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I'm not saying that leaky checkvalves in the fuel pump will drain the
float bowl.
I'm saying that once enough fuel evaporates/leaks in the float bowl to drop the float, and open the needle valve, leaky check valves in the fuel pump allow
everything from the needle valve down to the level of fuel in the fuel tank, to drain backwards. Air enters at the needle valve, and the plumbing drains down to the level of the gas tank, with the time required being dependent on how badly the check-valves in the pump leak. Adding a check-valve in the filter at the carb would prevent the back-flow of air into the plumbing, greatly reducing or eliminating the siphon-effect draining the tubing and perhaps the fuel pump.
If that allows air into the fuel pump itself, the pump is now vapor-locked and will have some trouble re-priming. Thus the "vapor return" plumbing on cars with A/C, and some others where the engine compartment is known to be particularly hot.
Even if the fuel pump doesn't get air in it, not only does it have to re-fill the float bowl, it also has to re-fill all the fuel plumbing on the pressure side of the pump that emptied-out.
Quote:
Originally Posted by Shiny
I don't buy into significant loss through the fuel hose.
Mine had a short piece at the pump and another at the tank. Call it 2 feet total.
I find J30R9 is spec'd and/or ceritified to have max permeability of 15 g/m^2/day at 40C (105F). Do the math for 3/8" hose and it might add up to 0.6 ml per day for that 2 foot section. At 70F, the loss will be a lot less, maybe 0.2 ml per day.
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My concern was that the original poster had rubber from front to back. I've seen guys do this because "it's too much hassle to route metal tubing through the frame."