Question asked by my son's and looking for the best answer other than it is working properly. We added an in-line glass fuel filter with the glass bowl like what should have been there when it was built. When we first installed it the bowl would fill with gas as the car was running, once stopped it would empty to the bottom of the filter. At this point we had fuel weeping at the fittings. Since fixing this weeping fittings the bowl stays full with gas even a day later.
My answer was that the weeping fittings were allowing air to get in and the gas was flowing back down the line till it hit that point, they thought the pump should have a one way valve on it to prevent back flow.
So I guess the big question is does the fuel stay due to there being no air leaks and secondly does the pump have a one way valve?
I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
"So I guess the big question is does the fuel stay due to there being no air leaks and secondly does the pump have a one way valve?"
is yes. The air leaks allow the gas to drain out of the line. Actually there are two one way valves. One before the diaphragm and the other after it. That is how the pump works. Fill the cavity created by lowering the diaphragm through the inlet valve with the outlet valve closed. Push out the gas through the outlet valve on the upstroke with the inlet valve closed. Any air leaks reduce the pumping efficiency down to zero.
Air leaks are by far the reason that a fuel pump does not work properly. Diaphragm and fitting leaks not only leak gas but also air.
Think of it like holding your finger over the end of a straw when you lift it out of a container of liquid. The liquid stays at the level it was when the straw was in the container.
I would not be surprised that after a few days of sitting the filter will empty. One reason will be the sealing efficiency of the check valve in the fuel pump. The other will be due to the gas evaporating out of the carburetor float bowl. The float will drop and open the needle valve. That will let air into the system (like taking your finger off the straw).
I guess this is all a good sine that we stopped all the leaks then. over 24 hours and the bowl is still full. I expected it to evaporate out of the carb but was thinking that may take about a week.
I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
If the check valve is really good the bowl will not empty even if the float drops.
You might be surprised at how quickly today's fuels evaporate. As a test just pour a little into a small open container and let it sit outside for a few days.
Now curiosity has me walking out to the car daily just to see how far the fuel level has gone down in the bowl. The car was last run Sunday afternoon. As of 10:00 AM EST on Tuesday the level is still high, picture attached. I only use non-ethanol fuel in all my small engines and the 87 Monte Carlo and 41 Master Deluxe. I also add StaBil when I add fuel regardless of how long they will be sitting. Is it possible that the non-ethanol and Sta-Bil make any difference?
I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
