klleetrucking

1970 Cutlass Supreme
350 completely rebuilt. (me) No Hi Performance stuff.
2 barrel carburetor (rebuilt by a pro shop)
New Carter fuel pump (3 line pump)
New fuel lines from tank to carb.
Inline glass fuel filter.
I've got about 250 miles on everything and it runs and drives good.
BUT, the other day after I shut it off I was watching the fuel filter and noticed a small air bubble travel through the filter towards the carb. It eventually drained the filter overnight.
With the engine running afterwards the filter will fill with fuel but have a small void and not completely fill 100%.
Then the following day after I drove the car I observed the fuel filter at idle. I can see the fuel rushing through the filter but it won't fill the filter but it still runs fine.
I've checked checked the oil many times to see if the engine is "making oil" and everything looks good.
There's no obvious puddles or odors of leaking gas and I've retightened every clamp and fitting.
This might be a "red herring" but the fuel pump is over 3 years old but only has maybe 6 hours on it.
Fuel pump gone bad?
Where is this fuel draining back to?
Thanks

joe_padavano

More posts have been written because of these transparent fuel filters than anything else.

First, if the car starts and runs reliably, you don't have a problem.
Second, the factory fuel filter in the carb has a check valve to prevent drainback. Clearly this aftermarket filter does not.
Third, the air pocket won't effect anything. Don't lose any sleep over it. This isn't a high pressure diesel injector where air matters.
Finally, if you have a mechanical fuel pump, the check valve in the outlet port of the pump should limit drainback like this. As the pump ages, the valves start to leak. This is compounded by ethanol causing deterioration, especially if the pump is older.

oldcutlass

If the car starts the next morning quickly, this a non-issue and there is no problem.

klleetrucking

Hmmm,
Starting quickly might be a matter of opinion.
The engine does have to crank maybe 6 - 8 seconds before it'll want to fire on the first start of the day. It's not instantaneous like does after running a bit.
I can tolerate the time it takes on the initial start.
My concern is, if it is draining back is the fuel getting into the oil
The other concern is the fuel pump failing and leaving me stranded.
I probably pull the glass filter and test it for leakage and maybe replace it with a solid metal one.

Thanks for the replies.

joe_padavano

People are spoiled by EFI systems with high pressure electric fuel pumps that prime the system before the starter motor turns. For carbureted cars that are not driven regularly, the fuel in the fuel bowl evaporates. This is normal. Cranking is necessary to refill the bowl. I'm guessing all your other vehicles are EFI. You do pump the gas pedal once or twice to set the choke and prime the motor before a cold start, right?

If the fuel is draining back, it is going into the fuel filter and from there back into the fuel lines. The only way it can get into the oil is if the diaphragm in the fuel pump is bad. If that were the case, your dipstick would reek of gasoline. Also, the oil level would keep going up.

If the fuel pump hasn't been replaced in a while, it would be prudent to get a new one as a preventative measure.

Sugar Bear

Rubber hoses between components can be pinched closed to narrow the location of leaks, e.g., fuel pump supply side.

Where is the glass filter? If it is on the supply side of the pump and installed with rubber hose consider eliminating it and going to steel tube.

Good luck!!!

klleetrucking

Where is the glass filter? - supply side between the pump and carburetor. It's one of those take apart deals that will be replaced later this week.
When I put the car together I used the late model rubber fuel injection hose in hopes of avoiding ethanol breakdown of the regular rubber fuel in the short sections where needed.
That fuel injection hose is STIFF and somewhat resistant to complying with my wishes, lol. I read the thread about the Wix 33003 filter and will try that along with the more compliant rubber hose. FWIW, I'm using new Ideal brand worm drive clamps.
I'm going to test the glass filter as well and report back.
Thanks everyone for your suggestions.

oldcutlass

Remove the glass filter and toss it in the trash, it’s a fire hazard.

klleetrucking

Follow up on drain back problems.
First of all I tested the glass style fuel filter with air and soapy water and no leaks.
I sent the carb back to the rebuilder and they replaced the booster, accelerator pump and the needle and seat.
Reinstalled the carb and the car runs good but the fuel still drained back as viewed through the clear filter.
Installed a brand new Carter three line pump and the drain back is the same. Although, maybe twice the filter has shown that the fuel line stayed full overnight.
I've put three fuel pumps in a vice in their proper orientation, set up a gravity feed to the line that feeds the carb and all three drain back fuel out the return line in less than a minute,
eventually draining the makeshift reservoir.
Two were new pumps.
Is this supposed to happen?
Is the function of the return line similar to that of an EFI system where any unused fuel is returned to the tank?
The problem is bad enough that the engine will start but sometimes stall because the pump hasn't caught up to the gap in fuel.
Is there any merit to the idea of converting to a two line pump?
I realize it's hard to diagnose these issues without actually being here.


.

joe_padavano

The stock filter in the carb has a check valve to prevent drainback. Apparently your aftermarket clear filter does not.

Falkon

Interesting read. There shouldn't be any filter between the fuel pump & the carburetor, except the original on the carb. Use a steel line. A solid metal WIX filter is good before the pump. Rubber fuel line on the engine is a fire hazard, as is a glass filter. Watching the fuel level through a clear filter is an exercise in futility. I replaced my fuel pump (seeped) & installed a new filter, at the carb. The car will start after 3 to 4 seconds cranking when sitting a week. Sometimes it takes longer. That builds up some good oil pressure. If it fires & stalls, mine does this after sitting 1/2 a day, crank & start again. Be sure your choke is adjusted correctly, plate closing cold, & pull off working. Then be sure it gets set when starting. You seem to be over thinking this.

klleetrucking

A very late follow up.
I'll try to be concise. The fuel in my car does drain back to some extent but through a very unscientific experiment (today's fuel), evaporation is a huge factor.
When I had the carb on the bench, I filled the bowl with fuel, took measurements and then replaced the lid (screws and all) to simulate the carb on the engine.
I let 24 hours pass and the evaporation rate was 40%.! So, if the engine isn't started for weeks, I've got an empty fuel bowl. Hence the cranking to get the engine to start,

The final situation is : removed all external filters and replaced with a straight line, pump > carb. I'm relying on the GM in carb filter and the sock in the fuel tank.
6/8 seconds of cranking to fill the bowl on initial start up and the engine fires. My car now runs and drives fine.

A side note, after I got the carb back from the "pro rebuilder" , the car would start and run/drive ok. BUT, it finally let me down in a very busy gas station. It would run ,only if I filled the carb bowl externally, and I managed to get the car onto to the side road. After I trailered the car back home, I ordered a good rebuild kit and meticulously rebuilt the carb myself. The problem was a sticking needle in the seat.

I should've listened to Joe, he's a smart guy.