Were big block fuel pumps..

[Bill Braun #33186]

...equipped with check valves in '67? I have a non-original fuel filter with a sight glass installed between the carb and pump. When I first bought the car, the sight glass was always full and the car fired right up. I notice now that I've got to crank the car longer to start it and, although the tank is full, the sight glass is empty. When I turn the car off and pop the hood, I can watch the gas in the fuel filter sloooooowwwwwly drain back to nothing. At first I thought the metal fuel line(s) to the carb were getting hot enough to cause vapor locking, but they are only slightly warm to the touch, and the fuel doesn't rise back into the filter when the car cools off. If the fuel pump has a check valve that isn't working, it would account for the fuel drainage, or are there other possibilities? Many thanks

Bill Braun

[motorman]

Re: Were big block fuel pumps..

any inline fuel filter should be installed vertically to keep them full of fuel. all original inline filters were installed from the factory in this position. check older corvettes. check your fuel pump for the number of fuel lines , if there are 3 one is the return line to the tank.

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[Jack H.]

Re: Were big block fuel pumps..

Not a matter of BB vs. SB.... Fuel pumps used internal 'umbrella' valves that acted as check stops (otherwise the pump wouldn't 'pump' effectively). Prior to the sealed pump introduction ('65 era), the pumps were assembled with a screw together body to facilitate re-building (kits still available from Paragon, Etc.). The rebuild kits consist of fresh/new gaskets for the multi-stage body assy, sets of new umbrella valves (inlet AND outlet side), as well as (some kits) fresh black phosphated body screws, pump level assy, rocker fulcrum and roll pin.

Appears that as field labor rates rose (relative US prosperity), it made less sense to R&R a failed fuel pump and rebuild it locally vs. simply scraping it and replacing it with a fresh new assy built in high volume assy line environment. So, when the need to do local rebuild disappeared, the requirement to allow the pump body to be disassembled also evaporated and we see 'cans' with crimped/rolled edges making 'em permanently seal.

Back to your original question, I don't believe a properly functioning fuel pump should allow appreciable 'backwash' when the engine is shut down....

[motorman]

Re: Were big block fuel pumps..

the third line i refered to is a calibrated leak on the pressure side of the pump that bleeds back fuel pressure to the tank after the engine is shut off to prevent excess fuel pressure to the carb to cause emission problems. this could allow the fuel to leave the filter and return to the tank because there is still enought fuel in the bowl to start the engine. later model carbs use a fuel filter that has a check valve and this acts like filling a straw with liquid and the putting your finger over the end and this keep the liquid in the straw. it prevents the the fuel line from going empty.

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[Jack H.]

But....

Original post constrained the thread to 1967 BB where tanks were vented vs. '70 and later cars with sealed evap recovery system. Guess I simply assumed we were talking about a factory stock single feed system. Did I miss something?

[motorman]

Re: But....

my main post was about the location of the in line filter, i just added the other facts as a matter of general info.

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[motorman]

Re: But....

there also has been some questions if chevy had placed some small holes in the pumps to bleed off pressure to the carb when the engine was not running. can not confirm this but it could be possible. there was a aftermarket kit that was attached to the inlet and outlet of the fuel pump to relieve the pressure to the carbs on the 427/435 HP vettes to cut down on the carb flooding problem.

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