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Expansion tank in bed


5veinte1

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It is not an expansion tank.  It is a liquid-vapor separator, and is part of evaporative emission control system.

 

There is a three port valve in the engine compartment, by the carburetor.  This valve has a connection to the air cleaner, the engine crankcase, and the upper connection on the separator.  There are three letters on the flow control valve, "A" "F" "C".  "A" goes to the Air cleaner underside.  "F" goes to the upper port on the separator.  "C" goes to the Crankcase.

 

Air can flow from the air cleaner, as the gas tank empties.  If pressure builds up in the gas tank, engine off, the air and fumes are pushed into the engine crankcase for storage.  With the engine running, the PCV system removes the fumes from the engine crankcase, and into the intake manifold.

 

Evaporative emission controls do not rob any horsepower from the engine.  Evaporative emission controls stop raw gas fumes from escaping away from the vehicle, this is a good thing.  It may even increase your gas mileage slightly.

 

I would suggest leaving it in place.

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Smog here is 1975 and older.  I don't have the valve in the engine compartment DanielC mentioned that I can see.  The fuel return is disconnected and capped both in the engine bay and at the tank location.  Currently I have the bed off on my hoist installing the tank.  Is the return necessary?  It looks like it would have to run across the engine from the carb to get back to the tank, and that seems weird to me.  I know on my other truck Soy there is a little silver thing that is held in the bracket on the passenger side of the engine bay.  I don't have pictures of that truck but here is what Wasabi has:

 

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I dont run return lines on my Datsuns. The mechanical pump goes limp when the carb has its bowl full.

 

I see your gas line is on the otherside. Hope you have fuel filters as 521s pick up alot of dirt in the tank from the fuel hose in the wheelwell.

 

you could just use a ink pen mark to mark TDC on the timming cover. its close to where that bolt hole will be. then use a stick or visually see the piston at the tiop and look at the timming sprocket lined up and assume your at TDC then mark the front cover. then use the indents on the crank for the BTDC using a light. SIMPLE.

 

Cant tell if your running points or a elelctric distributor. as zi dont see a ballast resisitor. so I assume you have a 3 ohm coil for a Pertronix or your electric matchbox dizzy. Long as it works for you. just ck if coil is HOT to the touch then you know you have a possible proplem.

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So I ordered a fuel filter yesterday because fuel filter.  Thank you for the redemption on the purchase.

 

hainz, I apologize in advance for my ignorance, but what you said about the timing I don't understand.  As I mentioned in another thread what I don't know about this could fill a book. 

 

I was told the distributor and ignition were electronic.

 

God I hate not knowing shit I should know about shit I own!

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The return line has a small restriction near the engine. The restriction allows the pump to build pressure so gas will flow into the carb and not all back into the rank. The hole isn't very large (larger than a pin hole) and allows some gas to return to the tank. I think all L20Bs have it because they run hotter under the hood and can suffer from vapor lock and hard restarts. The return constantly empties the fuel line near the carb of over heated fuel and any vapors from boiling and replaces it with cold fuel from the tank.

 

The return also vents any left over pressure back into the tank when the engine is shut off.

 

The thing I like best is ALL the fuel eventually gets circulated. This means ALL fuel is filtered over and over, removing any crap in it, keeping the tank cleaner.

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I like return lines because of the heat issue Mike just described, cool fuel in the lines.

I actually have a stock regulator on the back SU(or I did until I changed SUs), if it starts vapor locking I will have to transfer the regulator to the SUs on the engine now, but only have them issues in the summer when it is hot out, it is cool now.

 

I also have an electric fuel pump now(last few years), as sometimes when I parked the truck on a hill(front pointed up hill) and the engine stopped in just the right spot, the fuel would siphon back into the tank and I could not keep the engine running on the fuel in the bowls, it would die and would not start unless I used a screwdriver on the fuel pump arm to get the fuel back up from the tank, I believe the fuel pump had a small hole/crack in the diaphragm and it would not suck the fuel up from the tank when it was very hot out, but that little extra movement in the arm that it didn't get to while running was enough to pump the fuel out of the tank, it finally got so bad I converted over to an electric fuel pump.

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On a 521, the line from the flow control valve to the vapor separator tank is not a return line for liquid gasoline.  It is to vent air from the air cleaner, through the flow control valve into the gas tank as the pressure in side the tank drops as gas is used up.

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