Fuel draining back to tank after several min/hours of staying

bracketchev1221 wrote:Is the gas tank vented well?  Physics dictates that if the fuel line is below the tank, the line would need a pressure force on it to push it back.  Well, assuming the line is factory, it is below the tank.  The only other thing that can cause it is if the tank is not venting well and under vacuum, then when the tank tries to reach equilibrium it pulls the fuel back into the tank.  But the other question is how long are we talking of sitting.  My 80 Malibu does not like to start after sitting for about 2 weeks.  It cranks and cranks and then starts like the carb is empty, but its also hot in the garage so the carburetor may be vaporizing off as it sits.  

Joe73 wrote:Yes, I would ask the same question.  Is the vent open to air?  You should be able to slide under there and blow into the vent line to make sure its clear.  
Also, remove the filter before the pump and put it between the pump and carb.  You dont need the glass one.  And check the filter for a restriction.  

bigredlaguna wrote:I think your carburetor may be leaking out. The accelerator pump circuit may have enough to run the engine for a short bit since it draws from the bottom of the bowl, but the fuel level may not be high enough for the idle circuit to work properly.


I don't remember what carb you have, but you might use a small squirt bottle to fill the carb through its vents and see if it starts better.

Joe73 wrote:The vent tube on the sender is supposed to go the EVAP canister on the radiator support.  Theres a filter on the bottom of the canister and I believe charcoal inside.  The pcv valve regulates a vacuum on the evap canister which sucks in and burns gas fumes from the tank.  Its an emissions thing.

But I would grab that vent hose on top of your tank and blow into it just to make sure its clear.  

builtnotbought wrote:

bigredlaguna wrote:I think your carburetor may be leaking out. The accelerator pump circuit may have enough to run the engine for a short bit since it draws from the bottom of the bowl, but the fuel level may not be high enough for the idle circuit to work properly.


I don't remember what carb you have, but you might use a small squirt bottle to fill the carb through its vents and see if it starts better.

Edelbrock 1405 with man choke
I don't think carb holds inside so much fuel that will let engine work on idle and fill all fuel line from somewhere near tank to carb.
I read somewhere that pump diaphragm may leak fuel back to tank, in other place I read that pumps are designed to drain all fuel back:?:

Hm, squirt bottle sounds cool:D  but not every hour:D

I just don't know is it normal way of carburetered sbc operating or I have problems
It's not a big problem for me to crank it 2-6 times but I think it hurts battery and people who look at you when you try to get away in car but instead of this - sitting and cranking))))))

bigredlaguna wrote:

builtnotbought wrote:

bigredlaguna wrote:I think your carburetor may be leaking out. The accelerator pump circuit may have enough to run the engine for a short bit since it draws from the bottom of the bowl, but the fuel level may not be high enough for the idle circuit to work properly.


I don't remember what carb you have, but you might use a small squirt bottle to fill the carb through its vents and see if it starts better.

Edelbrock 1405 with man choke
I don't think carb holds inside so much fuel that will let engine work on idle and fill all fuel line from somewhere near tank to carb.
I read somewhere that pump diaphragm may leak fuel back to tank, in other place I read that pumps are designed to drain all fuel back:?:

Hm, squirt bottle sounds cool:D  but not every hour:D

I just don't know is it normal way of carburetered sbc operating or I have problems
It's not a big problem for me to crank it 2-6 times but I think it hurts battery and people who look at you when you try to get away in car but instead of this - sitting and cranking))))))

Edelbrock carbs have a good fuel capacity. The bowls are on both sides and are the length of the carburetor. They are notorious for heat soak and boiling the fuel out.

Do you smell a strong fuel odor? If so, from where? That information might help figure this out.

bigredlaguna wrote:https://www.jalopyjournal.com/forum/threads/carb-fuel-drain-back-problem.490971/

Here is a thread with some ideas. I suspect your fuel pump has some bad check valves or deteriorated materials inside.

Mcarlo77 wrote:

builtnotbought wrote:
Still no answer on how this cars must turn on from factory.

If you are asking how these started straight from the factory, I can tell you my bone stock, unmolested engine/carb will start after sitting all winter with about 5 seconds of cranking.  It's also how I remember it back in the day when all these cars were newer.  I push the pedal to the floor first to set the choke and then crank.  It's got the 350-4bbl engine.  

My '75 Laguna 350-2bbl stock set-up doesn't start quite so easily...but, still only takes a couple 5 second cranks to start after sitting for long periods of time.