why would someone remove the fuel rail on my l20?

[91b22]

so i have a 79 datsun 620, when i got it there was no fuel return line hooked up. i am runing a weber 32/36 so i know its not NEEDED, but i like things to be complete...

 

when i did some reserch, someone had ran a fuel line direct from the fuel pump to the carb and removed the fuel rail.... why would someone do this? any benefits from it?

 

i picked up a fuel rail at my local scrap yard to day and ill be hooking up the fuel lines accordingly.

 

 any info would be appreciated! thanks in advance.

[ggzilla]

There is no "fuel rail", instead there was a hard metal line with built-in return line. It connects via rubber hoses to the carb and to the fuel pump.

 

Guys remove parts which they think are unimportant. It's more important to the Weber 32/36 than to the stock carb. Because the L20B fuel pump puts out 3.8 psi and the return line has an orifice (jet) that lets a certain amount go back to the tank thus lowering the pressure. Weber says use no more than 3.0 psi.

 

If your weber is running good, no worries. But if it starts dripping gas, put a fuel pressure regulator in the line.

 

Redline Weber:

Fuel pressure is critical to float spillage.

Redline recommends 2.5 to 3 lbs.

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[91b22]

There is no "fuel rail", instead there was a hard metal line with built-in return line. It connects via rubber hoses to the carb and to the fuel pump.

 

Guys remove parts which they think are unimportant. It's more important to the Weber 32/36 than to the stock carb. Because the L20B fuel pump puts out 3.8 psi and the return line has an orifice (jet) that lets a certain amount go back to the tank thus lowering the pressure. Weber says use no more than 3.0 psi.

 

If your weber is running good, no worries. But if it starts dripping gas, put a fuel pressure regulator in the line.

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yeah thats what im talkin about. well ill be putting it back on.

[datzenmike]

Removing and making the fuel return line inoperative is totally retarded. It was introduced about the time the l20B came along. L20Bs tend to run hotter or make more heat and the fuel tends to boil while waiting to get into the carb. The cure is to have a return line to the tank with a small hole or restriction in to so the pump  can build some pressure to push gas into the carb. Without this restriction the gas would simply flow the easiest path back into the tank.

 

Top metal line..see the small hole? A hose connects this down to the return line on the frame rail.

 

Cool fuel is constantly pumped past the carb. Another advantage of this is the fact that the fuel is constantly filtered over and over and crap and rust does not collect in the tank.

[DanielC]

It was done to reduce vapor lock, a problem when gas boils, and turns to vapor in the fuel line, when it is hot.  The small hole does not really return that much gas back to the tank, but when you get vapor in the line, the small hole passes a lot of the vapor back to the tank, where it condenses back into liquid.

Meanwhile, the increased flow of liquid gas in to the hot fuel line cools the fuel line as it evaporates.

[LenRobertson]

So I'm not picturing in my mind a fuel return line on my '72 510. It is10F outside so I don't feel like going out and looking. What do 510 guys do when they stick on a Weber? I don't recall mention of the need for a regulator in the common "git a Weber" advice. The emphasis is always on how far to throw the Hitachi before installing the Weber. Or can that weird 3-way fitting on the driver's side strut tower that I always thought is a vapor vent line to the tank be used as a return line?

 

Len

[ggzilla]

Yes, cooler fuel evaporates less (EVAPO change). It was also done to later L16 in Japan, so it's not just an L20B thing. It is both to mitigate vapor lock and reduce emissions from evaporation.

[ggzilla]

Len the 510 fuel pump only puts out about 3.2 psi. Weber can handle this although Weber recommends a lower pressure. Some Webers can handle 5 psi if the float is adjusted correctly and the needle & seat are exceptional.

 

 

The Flow Guide Valve was an early method for tank venting, nothing to do with fuel return.

 

 

Flow Guide Valve was superseded by the superior charcoal canister.

[LenRobertson]

Okay, thanks. I still have high hopes for my Hitachi going back on (when it warms up outside) and it will run like a dream, but a Weber and rebuild kit are waiting in the wings. I forgot the stock fuel pump is low pressure. When I put the L20b in the 510 it had the 3 hard lines along between the carb and the valve cover. I hooked up one to the rubber line to the fuel pump, one for vacuum to the dizzy advance, and left the third unhooked cause I didn't need it. Luckily I was standing outside the car reaching in through the window the first time I cranked it. Gas went shooting out of the line I didn't need right on top of the battery. I figured out then it was a return line, so I plugged it off.

 

Len

[Z-train]

The small hole does not really return that much gas back to the tank,.

incorrect.It is constantly returning fuel to the tank.

[datzenmike]

 

Looks like a large darning needle hole. Maybe a little over a mm but not 2mm. Imagine 3-4 PSI pushing thin gas and that's what flows.

[DanielC]

When I said the small hole does not really return that much fuel back to the tank, that was in comparison to the output of the fuel pump, that should pump about 1 Liter, in one minute, at 1000 RPM.

Yes, it is constantly returning gas to the tank, except when it is passing gas vapors, and then is is functioning to prevent vapor lock.

[datzenmike]

Sorry was trying to say it does both.

[Z-train]

We're starting to get into sematics.It recirculates fuel to keep it cool,thus vapor doesn't form.

[ggzilla]

Yes, the meaning of words is very important.

[datzenmike]

We're starting to get into sematics.It recirculates fuel to keep it cool,thus vapor doesn't form.

Yes, the meaning of words is very important.

It will when you park it in 100+ heat and run in a store for 10 min. Ha!!! It still does both

[Z-train]

It will when you park it in 100+ heat and run in a store for 10 min. Ha!!! It still does both

Yep-that nevers happens in Tucson.

[highdesertdatsun]

 

A very easy solution for this return line in low pressure

and volume. I used this with success with small

Jiggle electric pump and stock mech pumps.

A 86 jeep cj7 w L6 engine has a 4 psi fuel pressure

Regulator built into fuel filter.look up on autozone

.com this can be adapted very easy to L20 fuel system

I have used on Volkswagen's works well off road

So float isnt overpowered by high revs and no return.

The filter has a outlet for return line and pops off at

4 psi.alot of jeep dudes remove them.

Causes all types of funny fuel system problems.like

vaporlock and the float bowl draining into hot intake.

I think they are great. I always use a Wix brand

[datzenmike]

The return line has a restriction in it. This is not going to lower the pressure or regulate it in any meaningful amount. The whole point of the restriction is so that pressure WILL build up on the carb side and push into the float chamber in the normal manner. 

 

[highdesertdatsun]

And when this pre determined orfice is removed from the fuel system may have odd problems

resulting in flooding and vaporlock. if this factory line is missing the filter described will

upgrade the orfice idea and provide a port for the return line. rather then just a orfice

how about a regulated valve at 4psi. ive done this repair of installing a jeep fuel filter with

the return line a couple times even added a fuel return line with jeep filter concept to a

off road rig to provide a more stable fuel supply. Ive even removed the float bowl level

plugs on a double pumper and plumbed them as a fuel return system for bumpy off road operation.

It worked awsome on the monster truck because it bounced so much. now there all injected if there

proclass .. I know Az and monster truck. I worked for a racing machine shop at the time and helped

tune truck in Phx. not many Datsun fans here in Prescott AZ . I grew up in San Jose . Thats when

I got Datsun fever. And its rekindled since I bought my 68 wagon or goon as you guys call em.

now I bought a 520. what have I started. sorry if filter post didnt make since. but think it though

it realy works great. but if I had a stock line I would leave it.