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

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

Post by builtnotbought on Tue Jul 24, 2018 7:25 am

Hello!

I have a question on this theme, may be somebody has some thoughts.
After I was trying to start engine hard cranking it several times (up to 5-6) after short/longtime storage to make it run I had an idea that fuel is dissapearing somewhere. Carb has some fuel anytime because first crank after 3 gas pedal steps makes engine work for 1-2 sec.
I noticed that after storage there is no fuel in fuel line at all. I have 2 filters, plastic one before pump and glass one after pump. There is no fuel even in plastic filter before pump.
I have 2 port fuel sending unit if I remember right, vent port is open and is staying above the tank under the body now.

Is there any solution besides elecric pump to make fuel stay in fuel line? May be I need to put a valve inline of maybe mechanical pump is bad? May be I'm doing smth wrong to vent port.

Thank you
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Fuel draining back to tank after several min/hours of staying Empty Re: Fuel draining back to tank after several min/hours of staying

Post by bracketchev1221 on Tue Jul 24, 2018 7:56 am

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.
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Post by Joe73 on Tue Jul 24, 2018 8:42 am

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.
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Fuel draining back to tank after several min/hours of staying Empty Re: Fuel draining back to tank after several min/hours of staying

Post by builtnotbought on Tue Jul 24, 2018 8:51 am

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.  

The line is factory. I beleive that line near the front a-arm is higher than tank and fuel goes back to tank under gravity.
I have rubber hose on the vent port of fuel sender and it's laying on the top of the tank, besides that tank cap is old with bad seal so I think venting is ok =)
At first I thought that if it sit for several days it turns on bad, but than I realized that after sitting 1 hour+ it won't start from first crank anyway.

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.  

Glass one came with engine, I just added plastic as it was in the previous fuel line sheme. I checked fuel pressure with 2 filters last season - it was ok.

Hm, I thought that if tank has an open way to air it will let fuel drain back anyway, and if tank is closed to air it won't let fuel go back as there is no way to air exit.
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Fuel draining back to tank after several min/hours of staying Empty Re: Fuel draining back to tank after several min/hours of staying

Post by bigredlaguna on Tue Jul 24, 2018 9:14 am

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.
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Post by builtnotbought on Tue Jul 24, 2018 9:26 am

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))))))
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Post by Joe73 on Tue Jul 24, 2018 9:35 am

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.
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Post by builtnotbought on Tue Jul 24, 2018 9:43 am

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.  

Yea I know this thank you, line was cutted near EVAP canister when I bought car and now EVAP is deleted at all.
I will try when the car will be on a lift in the nearest future, thank you
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Post by Hawk03 on Tue Jul 24, 2018 12:19 pm

Where should the fuel filter be, before the pump or after? I have mine before the pump but I see a lot of engines with them close to the carb.

Is the vent tube okay to be capped? I took out the canister and left the cap that came with the line.
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Post by Joe73 on Tue Jul 24, 2018 12:26 pm

Filter after the pump before the carb. I spoke with Holley tech about that. But if you have an electric pump its best to be gravity fed, if possible and filter before. But I've seen it both ways with electric. Electric can be a pusher or suction type.
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Post by bracketchev1221 on Tue Jul 24, 2018 1:39 pm

I put the fuel filter wherever it fits. My 78 Malibu and 70 Nova both had them off the tank under the back of the car. The Nova had a Fram canister tucked up between the rearend and the tank.
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Post by builtnotbought on Tue Jul 24, 2018 1:49 pm

So what is normal way of fuel system operation from factory on these cars? For how long fuel is staying in fuel line up to carb giving chance to start engine fron first crank?
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Post by bigredlaguna on Tue Jul 24, 2018 8:57 pm

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.
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Post by builtnotbought on Thu Jul 26, 2018 6:56 am

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.

No, no fuel smell at all outside of car. Pump gasket (between the halfs) is always wet, but I don't think it leaks fuel so much, no puddles or spots on the floor. Mystery cars.

I checked the car yesterday after sitting for 3 days, no fuel in line from pump to carb. Before pump plastic filter is full with no air. May be I was wrong telling that before pump filter is always empty - no air in it gave me wrong identification.
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Post by bigredlaguna on Fri Jul 27, 2018 12:23 am

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.
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Post by builtnotbought on Fri Jul 27, 2018 4:03 am

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.

Thank you!
Already read it before starting this thread Very Happy
Strange, because pump came new with engine. May be air is getting in line through bad pump gasket.

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


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Post by Mcarlo77 on Fri Jul 27, 2018 10:52 am

[quote="builtnotbought"]
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.


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Post by builtnotbought on Fri Jul 27, 2018 11:16 am

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.
Thank you Steve! Yes that’s what i wanted to know!

As for setting choke with pushing pedal to the floor, does this thing work with both manual and auto choke?
I wrote wrong above in my post, my 1405 Ed has auto choke. I was told to push pedal to the floor 3 times before first crank but don’t know if i’m doing it right.

What’s the right way to prepare engine start with auto choke and mexhanical pump?
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Post by Mcarlo77 on Fri Jul 27, 2018 12:00 pm

Both my cars have auto choke and, of course, factory style mechanical pumps. I have noticed it helps with the Laguna to slowly push the pedal to the floor twice before cranking. I've read where it's acceptable to do this as many as four times...although, I've never had to. But, once you do that, I wouldn't sit and pump the pedal WHILE cranking as you stand a good chance of flooding the engine.

Might just be my general disdain for the ethanol blend gas they forced upon us, but I do believe the non-ethanol 91 octane I use that is available for collector cars, recreational vehicles and small engines makes it easier to start these cars after sitting for long periods of time.
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Post by Joe73 on Fri Jul 27, 2018 12:05 pm

Non-ethanol if you can get it is the way to go in anything. Especially outdoor power equipment and boats. Octane wont make it easier to start. Higher octane only decreases the chance of engine knock. Which essentially allows you to bump up the timing more in most cases.
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Post by builtnotbought on Sat Aug 04, 2018 6:43 am

Found interesting thing, if after sitting for long period to push gas pedal 3 times than crank one time and after engine starts working - to push gas pedal a little bit and hold it - engine begins to work normally.

Order Moeller anti-syphon valve as in the link, will try it.
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