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mechanical fuel pump check valve?
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Mberglo
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PostPosted: Tue Jul 27, 2021 8:00 am    Post subject: mechanical fuel pump check valve? Reply with quote

I have a 71 Westy with a 1776 upright type 1 engine, using a Gen style fuel pump with the correct 108mm rod. I have dual genuine Weber IDF 40 carbs, and everything has 5000 miles on it. The bus sat for a week and it emptied the gas tank into the crankcase. I performed an experiment by putting clear tubing on both carb fuel inlets and filled the tube and float bowls with gas. I also pulled the fuel pump and placed a clean paper towel under it to monitor for leaks. After an hour or so, it's clear that the driver's side carb is leaking down and the pump is dry. I'll pull both carbs and clean them out and inspect the needle valves. The question I have is in regards to the mechanical pump. Should it allow gas to gravity feed through it to the carb while sitting? Should I replace that fuel pump as well?


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BFB
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PostPosted: Tue Jul 27, 2021 4:54 pm    Post subject: Re: mechanical fuel pump check valve? Reply with quote

is your gas tank venting "properly"? ive had several gas caps only vent to let air in but not out which causes the tank to build pressure in hot conditions and push fuel through the pump ( yes that can happen ) and fill the carb(s) to overflowing and into the engine it goes..
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busdaddy
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PostPosted: Tue Jul 27, 2021 5:33 pm    Post subject: Re: mechanical fuel pump check valve? Reply with quote

A solenoid valve mounted under the tank solves all those problems.

A 71 bus shouldn't have a vented cap, all the tank venting happens through the charcoal canister.
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74 Thing
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PostPosted: Tue Jul 27, 2021 7:02 pm    Post subject: Re: mechanical fuel pump check valve? Reply with quote

Fixing the needle/seat in the carb or replacing it should solve your problem. No check valves in the fuel pump.
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Mberglo
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PostPosted: Wed Jul 28, 2021 5:45 am    Post subject: Re: mechanical fuel pump check valve? Reply with quote

I removed the tops of my brand new Webers to find the float bowl widely out of adjustment. The float would basically go all the way to the top without seating the needle valve. These carbs went through an optional setup process from the vendor, so I didn't bother to check before installing them. Lesson learned there.

Still thinking about a square top Pierburg pump that has the integrated valve since the Webers sit 2-3 inches lower than a center mounted Solex, and the float line is below the tank bottom.
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67rustavenger Premium Member
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PostPosted: Wed Jul 28, 2021 6:07 pm    Post subject: Re: mechanical fuel pump check valve? Reply with quote

Always check new to you carbs. Even if you paid for them to be setup from a vendor.
Shipping can be a brutal process and knock things out of adjustment.

Choose whatever FP that you feel will work for ya. But the problem was the floats hitting the carb top(s), without closing the needle valve.

I have many dual carb setups. And they have never over flowed like you described. When they were checked and set correctly before installing them on an engine.
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