Fuel tank venting

[oldgasman]

Does anyone have diagram of what lines go where on the fuel tank lines and vent lines ?

It's for a 1970 Datsun 510 thanks

[loungin112]

That wouod be very helpful. Could i add a request for a 1972? Unless they are the same?

[Draker]

Just went through replacing lines on a 69.. ill see if can sort the lines out and post it up.

[DanielC]

Depending on the year, and location of original sale, your car may or may not have evaporative emission control.

Non evap emission cars vent through the gas cap.

Evaporative emission cars and trucks vent through a valve that allows air from under the air cleaner to go to the gas tank, but any pressure in the gas tank vents through the engine crankcase.

[CorAce]

This is a very good question. If my car sits for more than a day it smells strongly of gas inside. I dont think I have a vent at all.

[MicroMachinery]

Your 510 should have a vapor expansion tank. Maybe it got the vent tube removed or deleted?

[CorAce]

It got the vapor expansion tank deleted by the PO. But I still have it would that help?

[q-tip]

I have the same issue as corace, but I have a fuel pump where my evap tank once was. I ran a vent line out of the car under the trunk area, almost to the edge of the car. Still smells like gas though....

[Draker]

On my 69 there is a vent line from the top center of the tank and it vents via a tube that runs out below the vehicle. Right where the send and return lines come into the trunk. I'm trying to figure out.. is the top or bottom line the send line.. I am guessing it's the bottom is the send and the top is the return.

 

I checked on my 71 and there is no gas tank vent line on the tank.

[loungin112]

I've had taken a few photos of my trunk to help explain the part I needed tabbed for the filler neck. I'll post them Tuesday when I get home. I have an evaporating tank (I think) that is mounted to the roof of the trunk just behind the trunk lid and above the gas tank. Seems very complicated...especially when hearing that I could just vent it out of the car or out through the gas cap (somehow). What is the most efficient, durable way to vent a our gas tank?

[DanielC]

Evaporative emission controls are a good thing.  Basically, gasoline vapors get stored by a canister, or in the case of the early 1970 Datsuns, they use the engine crankcase to store vapors.  The vapors just get burned the next time you start the car, and a lot of times, your car needs a richer fuel air mixture then, anyway.

[CorAce]

Evaporative emission controls are a good thing.  Basically, gasoline vapors get stored by a canister, or in the case of the early 1970 Datsuns, they use the engine crankcase to store vapors.  The vapors just get burned the next time you start the car, and a lot of times, your car needs a richer fuel air mixture then, anyway.

so how do they get from the gas tank to the crank case?

[DanielC]

There is a valve in the engine compartment, with three ports.  This is it on a 521.  It is hard to see one port, it goes back, behind the valve.

The bottom hose goes to a small pipe on the side of the crankcase breather, that also goes to the PCV valve.

The middle port goes the vapor-liquid separator, the small tank in the trunk of a 510, or under an extension of the left fender well on a 521.  

The top port goes to the bottom of the air cleaner.

 

Air, or vapors can only flow down in the valve.  When you are driving, and using gas, air is drawn from the air cleaner, through the valve, and into the gas tank.  When you park your car on a hot day, gasoline vapors flow back to the valve, and can only go down into the engines crankcase.  When you srart the engine, gasoline vapors, along with blowby gasses flow throught the PCV valve, and are burnt.

 

[CorAce]

I know that valve, I remember taking it out but I don't remember it being hooked to anything. Do you have a flow chart for how it works?

[DanielC]

I thought I explained it, but here is another try.  This is a picture of the back of the valve.

The top port, with the "A" by it, goes to the Air cleaner.

The middle port, with the "F" by it, goes back to the vapor liquid separator by the Fuel tank.

The bottom port, with the "C" goes to the Crankcase.

 

[CorAce]

That's perfect thanks, I'll give a go at reinstalling it.

[Z-train]

OGM-that wouldn't be So.Cal.Gas Co.-would it?