# Vapor Return Line



## Hotsticker1 (Aug 20, 2017)

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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## PontiacJim (Dec 29, 2012)

Hotsticker1 said:


> 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. :thumbsup:


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## JNYBOY (Sep 28, 2017)

Hotsticker1 said:


> 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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## Hotsticker1 (Aug 20, 2017)

It is vapor lock, starter spins up fine.


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## tiretread (Sep 28, 2015)

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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## Lemans guy (Oct 14, 2014)

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.


:nerd::nerd::nerd:


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## Lemans guy (Oct 14, 2014)

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.:nerd::nerd::nerd::nerd::nerd:


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## tiretread (Sep 28, 2015)

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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## Lemans guy (Oct 14, 2014)

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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## tiretread (Sep 28, 2015)

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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## Lemans guy (Oct 14, 2014)

You are on it, could be the dirty fuel sock, filters can stall it. Did you order a sender with a return line? Usually 5/16 return.

A return line is the cure for vapor lock.

Let us how you do, credit is to you for staying with it!


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## tiretread (Sep 28, 2015)

Well, the old fuel sock was in pieces. I cleaned out the tank (no rust whatsoever in it) and I cleaned and re-painted the outside. I'll be putting the tank in tonight or tomorrow. I did not order the sender with a return line. Not sure but I thought the 65 389 set up didn't allow a return line. Seems like it wouldn't be too hard to do with the correct fuel sending unit.


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## PontiacJim (Dec 29, 2012)

tiretread said:


> Well, the old fuel sock was in pieces. I cleaned out the tank (no rust whatsoever in it) and I cleaned and re-painted the outside. I'll be putting the tank in tonight or tomorrow. I did not order the sender with a return line. Not sure but I thought the 65 389 set up didn't allow a return line. Seems like it wouldn't be too hard to do with the correct fuel sending unit.


The return line was used on AC cars. The fuel filter at the carb had three nipples versus the standard two. Your return line would have connected there. This has been covered before. Seems as the later 1968 and up cars used the return line coming off the fuel pump. https://www.gtoforum.com/f12/fuel-line-questions-111986/

The pieces of fuel sock were probably getting sucked up onto the fuel pickup tube and shutting off fuel flow. Had a similar experience when younger and it turned out to be a rag that someone undoubtedly used as a gas cap after losing theirs at a gas pump. The rag slipped into the tank. Removed the rag, and never a problem again.


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## Lemans guy (Oct 14, 2014)

Right the correct sending unit to beat vapor lock is the one with the return line. If you are putting one in that is the best option even if you just cap the return for now and later add the line. If it vapor locks on you you will be glad that you did.

The line is also much easier to run with the gas tank out......again you can cap it off and put it in in stages as well.


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## geeteeohguy (Feb 2, 2008)

Late to the party again, but what Lemans Guy and Jim said you can take to the bank. The '66 and '67 HD cooling cars had the return line run from a special canister fuel filter mounted 2 inches in front of the carb. As LG stated, it works better than the '68 and later return that ran off the fuel pump. My '67 came with HD cooling, and I ran with the vapor return bypassed in the 1980's, as I thought it wasn't needed. In the '90's, with the advent of crappier and crappier gas, I started to get vapor lock. I reconnected my Vapor Return, and the problem was 100% cured. And I live now where it's 30 degrees hotter in the summer. In 1988, on a trip from CA to Yellowstone in my '67, my car would surge and buck and die out every 10-20 miles. It was July, and I was in the Oregon desert. I crawled under the car and blew out the gas line with my mouth every time the car stalled. Then waited 30 minutes for the starter to cool off so it would crank over. When I got home, I pulled the tank and found the fuel sock wadded up into a ball. Cut if off and threw it away. Been running with no sock and no problems for the past 31 years. As for the no start when hot, I finally fixed that as well, simply by installing a new Solenoid wire from my ignition switch to the starter. I still have the same stock GM starter in the car I had then, only now it always cranks over when blistering hot. Win-win. I agree, adding a vapor return line on you car properly will have no down-side, and will make it much more tolerant of poor fuel.


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## tiretread (Sep 28, 2015)

Thanks for all the advice and tips. I have everything buttoned up but the car won't start. No fuel getting to the carbs. I blew the lines and there was the pop and then fuel rushing out the line. Still won't start. Car will start with some gas poured into the middle carb. In my frustration, I have pulled the fuel line, coming from the tank prior to the pump, three times. Each time I pulled it, there was little to no fuel coming out. Once I run some air thru the line towards the tank, I'd get the pop, and fuel would come rushing out. Any idea on what the issue is there? I'm about ready to just say the hell with it and get an electric pump.


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## PontiacJim (Dec 29, 2012)

tiretread said:


> Thanks for all the advice and tips. I have everything buttoned up but the car won't start. No fuel getting to the carbs. I blew the lines and there was the pop and then fuel rushing out the line. Still won't start. Car will start with some gas poured into the middle carb. In my frustration, I have pulled the fuel line, coming from the tank prior to the pump, three times. Each time I pulled it, there was little to no fuel coming out. Once I run some air thru the line towards the tank, I'd get the pop, and fuel would come rushing out. Any idea on what the issue is there? I'm about ready to just say the hell with it and get an electric pump.



Sounds like some crap in the line if you are blowing it out, getting a "pop", then fuel comes through. It would seem to me that when the fuel begins to flow again, whatever is floating around is once again getting sucked up into the line and blocking it again.

Double check you have the correct "vented" fuel cap and that someone didn't swap it out with a non-vented cap. A non-vented cap will quickly create a vacuum, especially with a full tank, and then your fuel delivery will stop - it can be severe enough to literally collapse a gas tank - maybe the "pop" you here is the tank being pressurized/inflated pushing it back into shape, or out of shape - tin canning?

Pull your steel line off at the tank where it is connected to it by a rubber hose. Make sure the hose is ethanol friendly. Old/wrong type rubber hose will deteriorate quickly and have seen then split and another collapse internally blocking off the fuel flow while looking good on the outside. Once the line is off the tank, then run your air through it and see if it is freely coming out. Then do the reverse just to make sure that whatever could be lodged in the steel line is not acting as a one-way check valve and when you blow from the rear forward to the fuel pump it plugs the line - like a flap of sorts.

Just go step by step and it should not be too hard to isolate. Just don't get frustrated. :thumbsup:


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## tiretread (Sep 28, 2015)

Jim, I appreciate the tips. I will get back at it tomorrow. It makes sense what you are saying about the lines possibly being clogged. The gas cap is the same one i've had since I had the car. Is there something obvious that lets you know it's vented vs. non-vented? Thanks again.


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## PontiacJim (Dec 29, 2012)

tiretread said:


> Jim, I appreciate the tips. I will get back at it tomorrow. It makes sense what you are saying about the lines possibly being clogged. The gas cap is the same one i've had since I had the car. Is there something obvious that lets you know it's vented vs. non-vented? Thanks again.


There may be a small visible pin sized hole on a vented cap. On a station wagon, I don't know if you have the vented cap or the filler neck vent hose that the GTO's had on the filler neck. Assume with a station wagon you have fuel door on the side of the quarter panel? You might have to look to see what your set-up is. https://www.gtoforum.com/f50/65-gto-fuel-tank-vented-cap-not-46586/

Just leave the cap loose as a test. My buddy has a 1970 Camaro with an electric fuel pump and could not figure out why his car would run out of gas, but still have plenty in the tank. Non-vented gas cap. Once he left the cap loose, it was able to draw air and problem solved. However, I don't think he ever got the correct cap, just leaves it slightly loosened. He drives like a little old lady, so no gas spills out.


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## tiretread (Sep 28, 2015)

I do have a vented cap. Say so right on it. lol. Don't know how I missed it. So I finally got fuel to the pump and to the carbs. Car started right up and I idled it for about 5 minutes and took off to get a full tank of non-ethanol. Got to one gas station, found out the pumps were closed, started the car right up and drove up the road for about a mile to another non-ethanol station. Fill the tank, take off and the car cuts off about 1/4 mile from the station. Lovely. Same issue as before. I sat for about 35 minutes and tried to start. It would turn over and catch for about a second or two and then go back to just turning over. Eventually, the engine stopped catching. Once again, no fuel to carbs. I got towed home and now I'm contemplating my next move.


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## RMTZ67 (Mar 12, 2011)

On my 67, I had what seems like the same issue. Mine had the return line on the fuel pump and sender. out of the blue I decided to use my compressor to blow the line back to the tank, and wha la, that pop the PJ mentioned. That was the source of my issues.Never cleaned the tank after that and never had the issue again. Try blowing out your carb to fuel pump line, then the fuel line at the fuel pump to tank. Just might be that simple.


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## PontiacJim (Dec 29, 2012)

tiretread said:


> I do have a vented cap. Say so right on it. lol. Don't know how I missed it. So I finally got fuel to the pump and to the carbs. Car started right up and I idled it for about 5 minutes and took off to get a full tank of non-ethanol. Got to one gas station, found out the pumps were closed, started the car right up and drove up the road for about a mile to another non-ethanol station. Fill the tank, take off and the car cuts off about 1/4 mile from the station. Lovely. Same issue as before. I sat for about 35 minutes and tried to start. It would turn over and catch for about a second or two and then go back to just turning over. Eventually, the engine stopped catching. Once again, no fuel to carbs. I got towed home and now I'm contemplating my next move.


Are you 100% sure it is a fuel issue and not an electrical issue? It seems to happen when the car gets hot, right? Have you ever pulled a spark plug wire and used a screw driver inserted into the end and see if you can get a good snappy spark going from the screw driver shank to the exhaust manifold - hold it close, but not touching.

Setting for 35 minutes should have been plenty of time for things to cool enough if it were vapor lock.

Points distributor? Could be a bad condensor. Electronic? Might be a bad module.

It would have been interesting if you had a little gas you could pour down the carb to see if it would catch, or a shot of starting fluid.

Does the engine have the tri-power, I can't remember. If it does, I would think you could manually work the end carbs to put a little gas in the engine - the bowls should be full.

Next test might be that if it quits and you are sure the bowl is dry, pull the line going to the carb (have rags ready to absorb any gas as you crack the line open) and have a catch can ready and see if cranking it over (coil wire pulled off) will pump gas into the catch can. If you have gas flowing, then it indicates carb problems like faulty needle & seat or sticking float. You might even consider a temporary clear glass aftermarket fuel filter plumbed into the carb line to see if you have fuel in the system when it quits.

Just going to take a little time and trial & error on this one.


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## tiretread (Sep 28, 2015)

PontiacJim said:


> Are you 100% sure it is a fuel issue and not an electrical issue? It seems to happen when the car gets hot, right? Have you ever pulled a spark plug wire and used a screw driver inserted into the end and see if you can get a good snappy spark going from the screw driver shank to the exhaust manifold - hold it close, but not touching.
> 
> Setting for 35 minutes should have been plenty of time for things to cool enough if it were vapor lock.
> 
> ...


No issue with spark and the engine does turn over and start with gas poured into the center carb (yes, tripower). I'll try pulling the fuel line off the carb and cranking it over with the coil wire off. But, I know fuel isn't getting to the pump. For some reason, it gas gets to the pump when I blow air thru the line, but it stops eventually. Lines clean, tanks clean, new fuel sending unit. I am wondering if maybe the sock in bunching up (as mentioned earlier by someone). I'll keep at it and hopefully find some time in the next week to diagnose.


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## tiretread (Sep 28, 2015)

Another re-visit from the past! Well, I finally figured out the starting issues. Bad fuel pump. Replaced with one I had lying around and the car started up just fine. Drove it this past weekend for about an hour seeing if the vapor lock/heat issues would raise their ugly head. Well, it seems after driving for an hour, and parking it for 15 minutes, I still had the symptoms of heat soak. It would start for about 10 or so seconds and bog down. No worries. I have a new tank, fuel sender (w/return line), a robbmc fuel pressure regulator, and a robbmc fuel pump waiting to go in the car once I get access to a lift. I will put in a 1/4" return line (either at the pump or at the regulator) and I think that will eliminate or at the very least mitigate the heat soak issue.


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## Lemans guy (Oct 14, 2014)

Robb MC stuff is tops!, ...all that will cure vapor lock. But remember Heat soak comes after shutdown,....like you are describing.

fixes for 1) conductive heat = phenolic spacer
2) Radiant heat = heat shielding, ( cool carb product will do both for you)
3) convective heat = fans, venting, removing hood blankets etc.

so do what you are doing, make sure you plan for all three types of heat. Sometimes just eliminating one of these will fix it.

good luck and let us know how you do!


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## tiretread (Sep 28, 2015)

Lemans guy said:


> Robb MC stuff is tops!, ...all that will cure vapor lock. But remember Heat soak comes after shutdown,....like you are describing.
> 
> fixes for 1) conductive heat = phenolic spacer
> 2) Radiant heat = heat shielding, ( cool carb product will do both for you)
> ...


I have the phenolic spacer and I have heat shield around the fuel lines near and around the block. I'm thinking of trying the cool carb product but not sure if that will do any better than the phenolic spacers I have on there now. I'm really hoping the return line helps cure that. I will look into putting in some fans as well because it sure does get hot here in SC in the summer! Thanks again for the tips Lemans guy.


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## gtoearl (Dec 21, 2009)

Interested in finding out how things turned out for you. I am planning on doing a return line in my 1966 Pontiac GTO tri power… having difficulty figuring out just how to route the steel line. I bought a coil of 5/16 tubing…If I have issues with that I’m thinking of going with the AN steel reinforced fuel line. Interested in how you ended up routing in your line..


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