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Air Pump & Fuel Return Question 1977 620 Pickup

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I'm going over the truck to put it back on the road  after it was parked in the garage for over twenty five years.


My dad took the belt off of the air pump. He probably thought the he was improving mileage /performance. Should I put the belt back on ?

The pump turns free, seems fine.


Second unusual thing I just found. While I was replacing wheel cylinders I noticed while doing the right rear that one of the rubber hoses going to the gas tank had been cut and plugged on both cut ends. I am thinking it is the fuel return line. Not sure why he would have done that. So should I reconnect the line ?


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You can try running the air pump. If there is noise or anything just disconnect it again.



The return line is aluminum, I think. The fuel pump moves more fuel than needed and a small amount is returned to the tank. This gas from the tank constantly moving past the carburetor boiling on hot days causing vapor lock and hard re-starting. As fuel constantly is being moved, all tank contents are filtered over and over and this keeps the tank clean. If you connect it up be sure fuel hose and not rubber and there are no leaks.

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OK I'll put the belt back on the pump it appears everything else is still connected. Will this effect the carb air mixture adjustment ?


On the fuel return line I was thinking about just putting a piece of 3/8 steel line in between them with hose clamps and see what happens....


Probably should blow air through them before reconnecting maybe ??

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No. it pumps air (with oxygen) into the exhaust ports valve. Hot exhaust with any unburned hydrocarbons should ignite and burn up.


Well it's unsure what that line is. If it goes to the fuel tank, it could be the return or the fuel vapor line.

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Ok then the pump is just forcing air into the exhaust to increase the air to hydrocarbons ratio going out the tail pipe. It seems like cheating on lowering emissions at the end of the tailpipe without really doing anything at the engine... 


On the fuel line, what I can see is the line is going into the top of the tank next to what must be the fuel line to the pump. I don't understand for the life of me why Dad would have cut and plugged this line, maybe if it was leaking, but I don't think that was the case. Why doesn't this return starve the carb. I'm thinking the gas would return to the tank and not have enough pressure to push gas pass the needle and seat in the carb ?? 

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That's the way the original emissions systems worked... they all produced emissions and the emission systems dealt with it. Today emissions systems are pro active and won't let engines do things that produce emissions.


The return line has a pin hole opening in it that restricts flow back into the tank. The pump builds pressure on the carb side so it will flow into the carb but a small amount squeezes back to the tank.  

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