68 1600 Fuel return line

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dads311
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68 1600 Fuel return line

Post by dads311 »

I know of a guy locally with a 68 1600 who says his car came with a fuel return line. He was telling me his mechanic said it was part of the smog control system. He also complains that if he doesn't start the car at least every week his fuel filter and carbs go dry and it is nearly impossible to start.He also said he put a new fuel pump on and now his mechanic wants to cut the metal line near the tank and put in a check valve.
I told him I have not seen a 1600 with a return line and when I suggested that may be what was causing his system to dry out and for the poor running of his car and he came back with "well my mechanic" and I stopped listening then. Why ask me if his mechanic says... So was I wrong, do the 68s have a fuel return line and does he need a check valve near the tank.
Mike
rebuilt dads 67.5 1600
1952 GMC 302ci 6cyl w/cam and 3 deuces
1965 Mustang (Wife's)
1971 Nova (Son Claimed)

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fj20spl311
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Re: 68 1600 Fuel return line

Post by fj20spl311 »

It has a fuel return line. I don't think it needs a check valve in the return line.

Most likely the fuel in the line is being siphoned back to the tank, maybe because of a one way air leak into the line or filter. A check valve in the supply line might help

The fuel filter should not be full if its clean, only dirty filters are full of fuel.
Phil
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notoptoy
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Re: 68 1600 Fuel return line

Post by notoptoy »

All 68 and up had the return line is my understanding - 1600 or 2000. Check valve might be a good idea, but I don't think I've ever heard anyone suggest that before. I think most people just block off the return line near that carbs and at the tank when they remove the smog stuff.
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bossbob
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Re: 68 1600 Fuel return line

Post by bossbob »

"I think most people just block off the return line near that carbs and at the tank when they remove the smog stuff."

Is this recommended, my smog has been removed, and the return lines are in place. I installed new rubber fuel lines not too long ago with a fresh filter, my filter and carbs go dry in a couple days if not started.

Should I block off the return line on my car?
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notoptoy
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Re: 68 1600 Fuel return line

Post by notoptoy »

There are some that feel that this return line helps prevent vapor lock - so the question of "should I" is not easily answered. If it were my car, I would at least temporarily block off the line at the carbs to see if it solves the problem, if so then permanently, if not, then I might leave it connected. How's that for an ambiguous answer? I have a 67.5, so I am not an expert on this, just relaying what I remember from other discussions.
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dads311
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Re: 68 1600 Fuel return line

Post by dads311 »

Well I stand corrected. I tried looking at pictures of other 68s and did not see a return line. I also have a 67.5 and have no idea. It just seems that a return line would severely limit the amount of fuel getting to the carbs.. path of least resistance thing. I can see a return line with an electric pump with more pressure, never heard of one with a mechanical pump.
I believe the carbs going dry is caused by siphoning fuel back to the tank. I will suggest they block the return line at the carbs to see if it helps the problem. Thanks guys.
Mike
rebuilt dads 67.5 1600
1952 GMC 302ci 6cyl w/cam and 3 deuces
1965 Mustang (Wife's)
1971 Nova (Son Claimed)

JT68
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Re: 68 1600 Fuel return line

Post by JT68 »

The return line does not limit flow to the carbs. There is a calibrated valve used on the rear carb that acts as a simple pressure regulator. The return line is operating when the carb bowls are full and the inlet valves are closed. Any extra fuel heads back to the tank. Its actually a good idea and intended to keep the fuel cool.
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dads311
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Re: 68 1600 Fuel return line

Post by dads311 »

Thanks JT. Is that something that the pre 68s should maybe have as well? I will have to check and make sure he has the valve in place. Would that valve also prevent siphoning of the fuel back to the tank or is that problem more of a possible air leak in the system? I love when I get to learn new things.
Mike
rebuilt dads 67.5 1600
1952 GMC 302ci 6cyl w/cam and 3 deuces
1965 Mustang (Wife's)
1971 Nova (Son Claimed)

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notoptoy
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Re: 68 1600 Fuel return line

Post by notoptoy »

One other thought, does he have the correct gas cap? Using a non-vented cap can create a vacuum in the fuel system. I think only 70's had a non-vented cap.
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dads311
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Re: 68 1600 Fuel return line

Post by dads311 »

Thanks notoptoy, I will check with him when I get home later this week.
Mike
rebuilt dads 67.5 1600
1952 GMC 302ci 6cyl w/cam and 3 deuces
1965 Mustang (Wife's)
1971 Nova (Son Claimed)