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Can we talk fuel return lines?
Posted by: flat_six ()
Date: November 18, 2020 08:50PM

I've seen multiple posts over the years on various forums. Usually someone has issues with flooding with their YH carb and the first response is "is your return line hooked up and working?".

Looking at the design, there is a nipple on the case of the GF-99 fuel filter. To that a hose runs to a 1/8" line forward to the gas tank where it dribbles returned fuel into the filler neck and into the tank.

The fuel pump on a Corvair draws (sucks) fuel from the tank and sends it to the filter/carb. Fuel pumps provide two things: volume and pressure. The pump volume is sized to cover the sustained WOT condition, and is therefore seldom reached. The pressure is determined by a spring within the pump.

So here's where I'm scratching my head regarding the presumed relationship between that fuel return line and fuel pressure. Being that the pump (with LARGE excess flow capacity for most operating modes) is feeding the carb in parallel a VERY tiny return line, I don't see any reason why there would be a significant relationship between fuel pressure at the carburetor and that return feature.

Since the smog engines (and some hipo Chevy V-8's of the era) also included a similar fuel return, I am inclined to believe that there is a relationship between this return feature and high under hood temperatures. Perhaps this return was really added by GM engineers to increase the flow of fuel through the inlet (suction) pipe within the engine compartment. This would decrease the temperature of the fuel in that pipe and decrease the probability of vapor lock occurring there on hot days and/or high elevations.

OK, now I'm sitting back and going into listen mode. Maybe I missed something?

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Re: Can we talk fuel return lines?
Posted by: playerpage ()
Date: November 18, 2020 09:36PM

Always been thoroughly confused by the return line. But I use it!

____________________________________________

Eric C. Player, Porterville, CA, USA (Seriously! It's the USA out here!)
MEMBER: CORSA National, Central Coast CORSA, South Coast CORSA, Vintage CORSA, Sfba CORSA, and the San Joaquin Valley Corvair Club.
THEN:
1965 Monza 110, Canary Yellow
1965 Corsa 180 Turbo, Red
1966 Monza 110, Purple
1967 Monza 140, Red
1966 500 110, Black; nicknamed "Shadow"
1965 Monza 110, Camaro Yellow; nicknamed "Silver"
NOW:
1966 Corsa 180 Turbo, Blue; nicknamed "Bluvair"

"He cautioned me not to take notes. It would not have helped if I had, as he would start a paragraph with, 'It is therefore obvious. . .'
and go on from there to matters which may have been obvious to him and God but to no one else."
-- Robert A. Heinlein, character of Daniel B. Davis, 'The Door Into Summer.'

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Re: Can we talk fuel return lines?
Posted by: joelsplace ()
Date: November 18, 2020 09:59PM

I agree with your assessment.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Can we talk fuel return lines?
Posted by: azdave ()
Date: November 19, 2020 03:44AM

joelsplace Wrote:
-------------------------------------------------------
> I agree with your assessment.

I would tend to agree too since pressure control is not achieved with a bypass or bleed-off type arrangement.

Remember, late model engines of all types had a fuel return line once smog engines appeared. That kind of tells you for sure the intention of that return line.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5



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Re: Can we talk fuel return lines?
Posted by: vairmech ()
Date: November 19, 2020 04:28AM

The return line is ONLY for vapor lock issues.

The return line has no correlation to the pressure to the carb and only an infinitesimal effect on volume.

What the return line does do is relieve the residual pressure to the YH carb. So in our case that is a good thing to relieve flooding after shutting down.

For those of you with the YH carb and no return not to worry, just get the fuel pressure down to 2.5-3.5 psi.

The 68-69 Cars had the return line for the above reason and also driven by emissions laws.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Can we talk fuel return lines?
Posted by: flat_six ()
Date: November 19, 2020 05:46AM

vairmech Wrote:
-------------------------------------------------------
> The return line is ONLY for vapor lock issues.
>
> The return line has no correlation to the pressure to the carb and only an infinitesimal effect on volume.
>
> What the return line does do is relieve the residual pressure to the YH carb. So in our case that is a good thing to relieve flooding after shutting down.
>
> For those of you with the YH carb and no return not to worry, just get the fuel pressure down to 2.5-3.5 psi.
>
> The 68-69 Cars had the return line for the above reason and also driven by emissions laws.


That makes sense. After shutdown, the fuel is heated further and expands in the line. Assuming that the check valves in the pump don't leak back much, the fuel pressure would potentially build fairly high if not for the return line. That could easily overwhelm the float valve in the carb.

Thanks for the summary Ken.

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Re: Can we talk fuel return lines?
Posted by: 66vairman ()
Date: November 19, 2020 09:55AM

Ken summed it up well. Folks sometimes assume the fuel filter acts as a pressure regulator, but to the best of my knowledge the "return" port is sized so fuel pressure is minimally impacted while allowing higher fuel volume through the pump and supply lines to minimize vapor lock. My recall could be wrong, but someone cut a turbo fuel filter open and posted pics here once upon a time.

I know from experience the 1962 model turbo without the fuel return line works much better with a fuel pressure regulator set to 2-3PSI per Steve Goodman's recommendation.

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Re: Can we talk fuel return lines?
Posted by: joelsplace ()
Date: November 19, 2020 01:32PM

I thought the factory filter had a valve and some of the replacements just had a fixed orifice. I could be totally wrong.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Can we talk fuel return lines?
Posted by: jjohnsonjo ()
Date: November 19, 2020 04:01PM

I have two NOS. Fixed orifice

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2013 KIA Optima SX turbo-AKA ZIPPY (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa


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Re: Can we talk fuel return lines?
Posted by: joelsplace ()
Date: November 19, 2020 06:23PM

Good to know. Thanks!

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Can we talk fuel return lines?
Posted by: Corveric ()
Date: November 19, 2020 09:30PM

I have a big Bore 4 carb in my rampside. I have an electric fuel pump at the tank which pushes fuel out at about 4.5PSI. I find it often overpowers the needles in the carbs which leads to a flooding issue if it is on for a few minutes. So my next thought is to install a fuel regulator, and in fact in another thread, a Holley 12-804 is suggested as it regulates between 1 & 4PSI. That seems ideal.

What my thought is that if the fuel pump was left running for any time with that regulator in place, we would avoid flooding, but would run the risk of an overheated fuel pump as it churns on the same small amount of fuel. (Does not sound like a good combination) so I keep thinking that a return line between the pump and the regulator makes sense so that there is always fresh fuel flowing through the pump to cool it.
Am I off track with that thought? I am interested in hearing other experiences and ideas. (I mean besides reminding me how daft I was for leaving it turned on)


I do realize that the ideal is to never leave the fuel pump running, but it has happened twice (in many years) accidently. One of those times was quite nasty. It filled the carbs which then leaked through to cylinders and the engine was in a hydraulic lock. Not a desirable condition. I know the guy who made that mistake, and I have never quite forgiven him for being so daft, but I have to wear his underwear so we have just agreed to never do it again. I am looking to ensure I do not make the same mistake again.

Eric near Vancouver, BC, Canada
'61 Corveric, '71 Triumph GT6, '63 Lemans, '72 Cheyenne s/b, '39 Chev COE project

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Re: Can we talk fuel return lines?
Posted by: joelsplace ()
Date: November 19, 2020 09:59PM

I've always thought any good regulator would use a return line.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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Re: Can we talk fuel return lines?
Posted by: RobertC ()
Date: November 19, 2020 10:59PM

Corveric Wrote:
-------------------------------------------------------
> so I keep thinking that a return line between the pump and the regulator makes sense so that there is always fresh fuel flowing through the pump to cool it.
> Am I off track with that thought? I am interested in hearing other experiences and ideas. (I mean besides reminding me how daft I was for leaving it turned on)
>

Do not know all the combinations for electric fuel pumps or electric fuel pumps used in Corvairs, but do not think a return line between a regulator and an electric fuel pump is of any benefit.

Electric fuel pumps used on Corvairs (the ones I am aware of) do not have any needed additional cooling via fuel and last for many years.

It seems you are confusing the modern electric fuel pumps placed in the tank that appear to fail if they are not covered in gasoline.

Sounds like your electric fuel pump is only powered by a toggle switch - not via the ignition switch with an oil pressure switch - or even through a "dead man's switch".

So, if you were incapacitated in a wreck, there would be no one to turn off the electric fuel pump - or even know it was there.

That seems more important to me.

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Re: Can we talk fuel return lines?
Posted by: Corveric ()
Date: November 19, 2020 11:36PM

The fuel pump is powered only by the ignition switch to 'ON'

I do have a 'dead man's switch'. It is from a Ford I believe and is a re-settable switch which is triggered by impact - I believe it is known as an inertia switch. I am not really familiar with it, but I know it is on the front wall of the cab near the brake pedal.
Really just wondered about the possibility of overheating the pump. Of course, it is under the truck mounted to the crossmember immediately behind the fuel tank so it is in open air. Maybe not an issue, I saw this thread and thought this fit in as another reason for one.

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Re: Can we talk fuel return lines?
Posted by: RobertC ()
Date: November 19, 2020 11:58PM

Corveric Wrote:
-------------------------------------------------------
> The fuel pump is powered only by the ignition switch to 'ON'
>
> I do have a 'dead man's switch'. It is from a Ford I believe and is a re-settable switch which is triggered by impact - I believe it is known as an inertia switch. I am not really familiar with it, but I know it is on the front wall of the cab near the brake pedal.
> Really just wondered about the possibility of overheating the pump. Of course, it is under the truck mounted to the crossmember immediately behind the fuel tank so it is in open air. Maybe not an issue, I saw this thread and thought this fit in as another reason for one.

Good. My feeble mind could not come up with a reason - guess you had the ignition in the "ON" position testing an electrical problem.

Have not read anything about electric fuel pump failures in Corvairs. Seems the pumps last for decades.

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Re: Can we talk fuel return lines?
Posted by: joelsplace ()
Date: November 20, 2020 11:00AM

Cooling the pump doesn't make any difference that I can see on the diaphragm type pumps but it should help the rotary pumps. All modern vehicles I know of use a return line and they all use rotary pumps.

Joel
Northlake, TX
5 Ultravans, 113 Corvairs and counting...

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