69 fuel leak on return line near fuel pump

[Richard R.]

Just started up the engine on my 69 L46, 350/350. It hadn't been run since it was rebuilt about 6 years ago. I took the precaution of removing the plugs and squirting in some fogging oil, turned the engine over with the plugs out until oil pressure started to build, then put it back together and gave it a spin. After fussing with the plug wires, it started and ran great until I had to shut it down for fuel leak problems. leaking from the fuel filter line and from the return fuel/vent line.

The thing that puzzles me most is the return line. That line has simple spring clamps and I had to temporarily put a screw type hose clamp on it to stop the leak. This was at the end of the steel line near the fuel pump where the rubber hose connects to it. It was steady drip, almost a stream. It also is ozing at the other end of the rubber hose that connects to the steel line that runs up to the fuel filter. Why is there so much fuel in this line? Is the fuel filter defective? I just can't believe the original design of these little spring clamps anticipated much if any fuel in that smaller line.

Any suggestions on how to deal with this?

Thanks much,

Rich

[Michael L.]

Re: 69 fuel leak on return line near fuel pump

Rich,

I don't think the presence of the spring clamp is an indication of how much fuel is supposed to go through the line, since those style clamps are used on all the fuel lines from this year and on the L-46 model as well as on all the other models I believe. If your other lines do not have these spring clamps then it's because they have been replaced. Given what you said about the fact that the car sat for 6 years I have no doubt what has happened is the rubber lines have dry-rotted at the point where they are over the metal lines and need to be replaced. likely the worm style clamp you added managed to plug the hole that was there but it still should be replaced.

Mike

[Richard R.]

Re: 69 fuel leak on return line near fuel pump

Mike,

Thanks for getting back to me. I would agree if the plumbing was original or old that perhaps there was a problem with hose, but everything is new and per original specs. I read the AIM again and they refer to this line as a fuel vapor line that returns to the gas tank. If it is a vapor line then there should be no fuel in it al. I'm thinking the new repro fuel filter is a problem. Still working on it.

Rich

[Bill M.]

Re: 69 fuel leak on return line near fuel pump

Rich mike is 100% right change the fuel lines you may also spring a leak in your fuel pump soon I would change that now as well.

[Mark E.]

Re: 69 fuel leak on return line near fuel pump

Mike,

Thanks for getting back to me. I would agree if the plumbing was original or old that perhaps there was a problem with hose, but everything is new and per original specs. I read the AIM again and they refer to this line as a fuel vapor line that returns to the gas tank. If it is a vapor line then there should be no fuel in it al. I'm thinking the new repro fuel filter is a problem. Still working on it.

Rich

It's curious AIM refers to this as a fuel vapor line, because it isn't. The line originating from the filter and going to the tank is a fuel return line. It allows fuel to continue circulating even when the carb's needle and seat is closed to help prevent vapor lock. So this line definitely has fuel in it.

As advised above, check and replace the rubber lines if they show any swelling, cracking, or if they are not new.

[Joe L.]

Re: 69 fuel leak on return line near fuel pump

It's curious AIM refers to this as a fuel vapor line, because it isn't. The line originating from the filter and going to the tank is a fuel return line. It allows fuel to continue circulating even when the carb's needle and seat is closed to help prevent vapor lock. So this line definitely has fuel in it.

As advised above, check and replace the rubber lines if they show any swelling, cracking, or if they are not new.

Mark------


Yes, fuel vapor return lines only exist on 1970+ Corvettes also equipped with EEC systems (1970 with NA-9 and all 1971+). However, these fuel return lines often are referred to as "vapor return lines". They are NOT. All 1968 and later C3 Corvettes equipped with Rochester carburetors were equipped with fuel return lines.

[Joe L.]

Re: 69 fuel leak on return line near fuel pump

Mike,

Thanks for getting back to me. I would agree if the plumbing was original or old that perhaps there was a problem with hose, but everything is new and per original specs. I read the AIM again and they refer to this line as a fuel vapor line that returns to the gas tank. If it is a vapor line then there should be no fuel in it al. I'm thinking the new repro fuel filter is a problem. Still working on it.

Rich

Rich------


Original rubber fuel lines were larger in OD than most current rubber replacement fuel lines. Spring clamps used on fuel lines were designed to work properly within a relatively narrow range of hose OD. So, if you are using original hose clamps (or, identical to original hose clamps) with hose which is smaller in OD than original hose, you'll likely have a leak.

[Richard R.]

Re: 69 fuel leak on return line near fuel pump

Below are two pictures from the AIM (7&8 of B3). Page J229 calls it a fuel vapor return line. Page J230 calls it a fuel return. This is what was causing my confusion. I'll pull the offending hose off and get another. I can't recall where it came from. Joe, do you know what the original OD rubber fuel return line was?

As it turns out it is leaking at both ends of the same short rubber line. Nothing at the tank end though.

IMG_6488.jpgIMG_6487.jpg

[Mark E.]

Re: 69 fuel leak on return line near fuel pump

Judging points aside, worm gear clamps provide a better, more reliable seal than spring clamps which can lose tension with age. Also, hose OD variance is not an issue with worm gear clamps. If you drive this car, I wouldn't mess with spring clamps, especially on fuel lines.

Back in the day, it was common (at least among guys in my circle) to toss the spring clamps. Maybe that's why original ones with square ends are rare today.

[Joe L.]

Re: 69 fuel leak on return line near fuel pump

Below are two pictures from the AIM (7&8 of B3). Page J229 calls it a fuel vapor return line. Page J230 calls it a fuel return. This is what was causing my confusion. I'll pull the offending hose off and get another. I can't recall where it came from. Joe, do you know what the original OD rubber fuel return line was?

As it turns out it is leaking at both ends of the same short rubber line. Nothing at the tank end though.

[ATTACH=CONFIG]116343[/ATTACH][ATTACH=CONFIG]116344[/ATTACH]

Richard------

The term "fuel vapor return line" in the AIM is a misnomer. Among other reasons, there would be absolutely no point in returning fuel VAPOR to the fuel inlet line at the fuel filter (1968-69) or the fuel pump (1970+)

I do not know what the OD was of the original rubber fuel line. However, if you use the worm screw type clamps and it solves your leak problem, then you'll know that the problem I previously described is the root of your leak problem.

[Joe L.]

Re: 69 fuel leak on return line near fuel pump

Judging points aside, worm gear clamps provide a better, more reliable seal than spring clamps which can lose tension with age. Also, hose OD variance is not an issue with worm gear clamps. If you drive this car, I wouldn't mess with spring clamps, especially on fuel lines.

Back in the day, it was common (at least among guys in my circle) to toss the spring clamps. Maybe that's why original ones with square ends are rare today.

Mark------

Yes, worm screw type clamps were/are often substituted for the spring type clamps. However, there is one advantage to the spring type clamps. These clamps provide constant pressure through their operating range. In other words, as the hose gradually deforms due to the pressure of the clamp, the clamp in-turn automatically "adjusts" to maintain sealing pressure. Worm screw clamps do not automatically adjust and may need tightening from time-to-time.

[Richard R.]

Re: 69 fuel leak on return line near fuel pump

Thanks much guys. I appreciate your help!

[Richard R.]

Re: 69 fuel leak on return line near fuel pump

Well I finally got to this on my punch list and discovered the problem. Take a look at this picture of the line. It is like this on both ends so I imagine it was that way through the piece. Perhaps it was stepped on before I bought it. Clearly I missed it when installing it or thought the creases would not impact sealing. Regardless a new 1$ 6" x 1/4" solved the problem. All's good.

By the way, the service manual also calls this a fuel "vapor" return line. Clearly it isn't.

Rich

fuel return hose.jpg