Vapor Return Line - Pontiac GTO Forum
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post #1 of 22 (permalink) Old 05-10-2018, 04:39 PM Thread Starter
 
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Vapor Return Line

I have a 65 GTO, 389 Tri Power, 4 speed completely stock except bored out 30 over no A/C. After rebuilding carbs, replacing vacuum hoses, replacing distributor she is running very good however since its getting warmer out here in the southwest it has vapor locked a couple times after shutting off and heat soak, does not want to start until about 30 min of cool down. I have read that I should install a vapor return line back to the full tank to remedy this problem. Can someone one here tell me the proper way. Should I purchase a fuel tank sending unit with the return line or just run a return line to the nipple located on the fill neck behind the license plate?
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post #2 of 22 (permalink) Old 05-10-2018, 05:15 PM
 
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Originally Posted by Hotsticker1 View Post
I have a 65 GTO, 389 Tri Power, 4 speed completely stock except bored out 30 over no A/C. After rebuilding carbs, replacing vacuum hoses, replacing distributor she is running very good however since its getting warmer out here in the southwest it has vapor locked a couple times after shutting off and heat soak, does not want to start until about 30 min of cool down. I have read that I should install a vapor return line back to the full tank to remedy this problem. Can someone one here tell me the proper way. Should I purchase a fuel tank sending unit with the return line or just run a return line to the nipple located on the fill neck behind the license plate?
You want to do this correctly and safely. The nipple on the filler neck is for a hose/vent. Would not be smart to have gas pushing through that close to the cap and you would most likely eliminate the function of the vent and wind up with other fuel problems you will have to sort out.

This has been covered a number of times and I believe recently by another member who had a '65 (?) and was searching for a fuel tank sending unit with the 1/4" return fitting so he could add a return line as well. Make sure ALL rubber line is updated to ethanol friendly hose.

If you do a search using the SEARCH feature on this forum up there in the upper right, you should be able to pull up several topics that cover this. It was found that those cars with the AC came with the 1/4" return line and filter having the return line feature, while the non-AC cars did not. So you should find a good many posts to help with adding one to your car.
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post #3 of 22 (permalink) Old 05-10-2018, 09:16 PM
 
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Originally Posted by Hotsticker1 View Post
I have a 65 GTO, 389 Tri Power, 4 speed completely stock except bored out 30 over no A/C. After rebuilding carbs, replacing vacuum hoses, replacing distributor she is running very good however since its getting warmer out here in the southwest it has vapor locked a couple times after shutting off and heat soak, does not want to start until about 30 min of cool down. I have read that I should install a vapor return line back to the full tank to remedy this problem. Can someone one here tell me the proper way. Should I purchase a fuel tank sending unit with the return line or just run a return line to the nipple located on the fill neck behind the license plate?
Sure it's Vapor Lock ?..The symptom you describe could also be attributed to a Starter in which the Windings are breakin' down due to the heat it is subjected to, over time....Had the problem a couple years back...New Starter, No more problem, in my case ....Best ,. j
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post #4 of 22 (permalink) Old 05-10-2018, 09:20 PM Thread Starter
 
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It is vapor lock, starter spins up fine.
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post #5 of 22 (permalink) Old 03-18-2019, 08:30 PM
 
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Sorry to bring this back but I have the same issue with basically the same set up except mine is an automatic 65 Tripower. I searched but haven't found the thread stating how to do this correctly. What did you end up doing and if your utilized a particular thread, could you help direct me there? Thanks in advance.
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post #6 of 22 (permalink) Old 03-19-2019, 04:34 PM
 
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I have dealt with all this so let me build on what was said already, and correctly I might add.

Two one is Vapor Lock, which occurs while driving and stalls the car.....the other is Heat soak which occurs after shutoff and fuel boils in the carb and lines.

Vapor lock first. The cure for vapor lock is a return fuel line to the tank. This is also how the factory fixed it by starting to add that return line from the fuel pump. That works ok. But the best is a return line right at the carb since it keeps the fuel flowing and cool all the way up.

you start with a fuel sending unit that has a return line usually a 5/16 return line. You will just link to that sender with a rubber hose and then to steel fuel line. The hardest part is running the steel fuel line. "Inline tube" has the line and the sender. You can also cut that line in half and put a coupler in the middle of it and it would make the install much easier.

get a garage with a lift to install it you just put it in dry. At the front where it exits the frame hole you have another rubber connection to the pump or to more steel fuel line. If your current pump does not have a return line on it buy one that does, some of the Air Conditioned GTO, Lemans etc had a pump with a return line. so that is an easy route and will beat your vapor lock as it occurs on the suction side of the pump.

Instead of changing the fuel pump you can run a Wix fuel filter 33041, that has a return line built in. That filter acts the same as the return on the pump and will prevent vapor lock. It has a small about 060 orifice that returns the fuel just like the pump does. you just connect to the 5/16 steel with rubber hose. Their is also a mounting thing for that fuel filter, check Ames catalog, it mounts on the intake.

Now the best way, what I do and many others is a return line from the carb fuel line, after fuel goes buy both bowls of the QFT carb a steel line button hooks back, inside is a connector with a welded slug and I drilled an 060 orifice in that fuel. Fuel never stops moving past the bowls, and it stays the coolest. An added method would be to run a fuel regulator at the end of the fuel log, same thing fuel keeps moving.

All must have the return line to the tank and sending unit. then you can run it to pump, or Wix 33041, or from the fuel log with orifice or regulator.


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post #7 of 22 (permalink) Old 03-19-2019, 04:50 PM
 
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so what I mean by putting in Dry is just to plug tyhe 5/16 sender return until you are ready to make the final connection.

Now heat soak. after shutdown the fuel boils in the lines bowls and causes hard or no start. Todays reformulated gas has a low distillation curve.

summer blend pure gas starts boiling near 170 degrees, E-10 around 140 degrees. winter blend is even lower. the change over is in May usually so get fresh summer gas.
Pure gives you a little advantage.

Now you deal with 3 Heat types Conductive, Radiant, and Convective. The fix for conductive heat, metal to metal, is a phenolic spacer under the carb,Check with "DashMan" on the web he has a site and sells the Phenolic spacers and will get you the right one.

Next is radiant heat, it effects some carbs more than others Holley and QFT hang the bowls out over the intake , it gets hot and radiates heat to the bowl. some Carbs have more internal bowls and not so much of a problem, but your fuel lines and filter get radiant heat as well. The fix for Holley and QFT is radiant heat shields under the carb. Holley sells them, Mr Gasket and "Cool Carb" has one that acts as both a phenolic spacer and radiant heat blocker. It just cannot be used if your exhaust crossover is open.

mine is, so I use the aluminum shields with DEI heat tape on them. Your fuel lines can be kept cool with DEI fire sleeve. Summit and Jegs sell it or DEI direct.

Convective heat is another challenge, when the hood is shut after a long drive the under hood temps get very hot like an oven, and boil the gas..phenolic spacer or not.

when you stop at the car show open the hood all the way, it helps the heat leave. Some guys say they don't have the problem but only drive to the car show and open the hood for 3 hours and they are ok. The real test is drive for an hour at highway speeds and then go in a restaurant for an hour with the hood shut, different story.

I use fans on time delay relays to dissippate that heat on real hot days and it works good.

Alternatively you can get fuel injection and because the fuel is under pressure you don't have these problems, it's boiling point is raised by the pressure.

best 2 things run a return line any way you choose and use a phenolic spacer. Then see how things go.
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post #8 of 22 (permalink) Old 03-19-2019, 07:51 PM
 
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Lemans Guy, much appreciation. I just put phenolic spacers on from Mike Wasson and still have the heat soak (drives fine but when I park it for and shut it off, it has issues. I have to wait about 30-40 minutes until the car will turn over and stay running) issue. I'm going to put some non-ethanol fuel into it tomorrow and drive it to Myrtle Beach (2 hours) for a car show tomorrow. I'll look into the fans on time delay. Thanks so very much for your feedback.
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post #9 of 22 (permalink) Old 03-19-2019, 09:02 PM
 
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Good luck tiretread,...once you get to the car show open the hood right away,...it will decimate much of the heat. If it is breezy in Myrtle Beach, often it is,....once parked face that engine to get the breeze! Free cooling.

What happens is the fuel will boil in the carb bowls and lines as all the heat tries to reach equilibrium, hot always goes to cooler items.

If you stop at the parts store ”Stabil 360 Marine” helps a little bit. It has a very high vapor front to keep gas stabilized and that goes on your side a tad only though.

It is hard to start cause your carb bowls are empty. Try this after the car show, set the choke with your pedal all the way down, once. Then crank 3 seconds and stop don’t even try to start it . Wait 20 seconds do it, and once more. What you are doing is using the fuel pump to put some fuel back in the carb bowl.

So now you have some fuel in the bowl hopefully, but it is not full. So two good squirts from the accelerator pump with your foot and one last all the way, to make sure choke is set. Wait 30 or 45 seconds and let the fuel settle down over the valves. Then try to crank it...

Sounds complicated but really simple, just working the pump choke and fuel to your advantage.

Have fun! Heat soak is only after shut down while driving the air moving thru prevents the boiling fuel.
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post #10 of 22 (permalink) Old 03-28-2019, 10:08 AM
 
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Just a follow up: Almost made it to the show. Vapor locked about 3 miles short of the registration site. Kept hitting all the lights just prior to getting there. Opened hood, waited 20 minutes, started up and drove to the hotel to register for the show as well as our room. Got into the car 40 minutes later and drove the remaining 5 miles to the show site. Upon leaving the show (70 degree breezy weather) I made it almost 4 miles before vapor locking. Actually, my fuel gauge is doesn't go below the 1/2 way mark and I may have actually been out of gas. d'oh. No worries, get fuel, and car starts up and I drive about 20 miles to a non-ethanol station to fill up. Vapor locked for about an hour before it gets going again. make it the rest of the way home with no issues.

Dropped the tank and emptied it of fuel. There was definitely "stuff" in the fuel but the tank looks relatively clean. I have ordered a fuel sending unit and will clean the tank out with some diesel prior to install. I also ordered some heat shields (DEI) for the fuel lines. If this doesn't work, I'm most likely going to go whole hog and get an electric fuel pump installed. I'll keep you updated (if anyone is interested, lol). I'll post some pics of the fuel sock when I pull it and replace with the new. I'm thinking this might be a primary culprit for this issue.
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