Vapor lock issues? - Vintage Mustang Forums
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Old 07-02-2018, 10:02 AM Thread Starter
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Vapor lock issues?

Now that summer is back in full swing in the northeast I've been finding myself in traffic on hot sunny days more often, and lately have been having issues with vapor lock in my fuel system. Wondering if anyone can say based on your experience at what point vapor lock becomes a problem if the fuel system is working properly?

For context, had a vapor lock-related breakdown in stop and go traffic on the highway the other day (got it going again after ~10 mins cooling down so no harm done). That was after 20-30 minutes of stop and go in the sun in 90 degree weather. Is that indicative of a problem or is that just to be expected w/ mechanical fuel pump?

Replaced all the fuel lines last spring and a new Carter pump and filter this spring (stock 302) so I'd expect everything should be working properly, but wanted to see if there are red flags I'm missing.

Secondary question, what could I do to avoid breakdowns like the one described above? Considering either a second electric pump back near the tank, or getting an EFI tank and running a pressure regulator until I upgrade the motor to EFI.

Thanks in advance for any tips!


1967 coupe in dark blue w/ a 302 and 3 speed from a '68
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Old 07-02-2018, 10:41 AM
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Quote:
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Replaced all the fuel lines last spring and a new Carter pump and filter this spring
Did you use a metal line between the pump and the carb?
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Old 07-02-2018, 10:59 AM
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A 1/4-1/2" phenolic spacer between the carb and intake is a given "standard" preventer too.

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Old 07-02-2018, 11:17 AM
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I never had a Vapor lock issue in a Ford.... but I had a 1995 Caddy with an LT1 that had bad Vapor lock problems real bad. The solution?? All I did was drill a good sized hole in the middle of the gas cap.... Problem solved... The car never died again...

)

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Old 07-02-2018, 11:48 AM
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Are you sure it's vapor lock? I had the same problem and it turned out to be a bad coil. Coils don't act the same cold as they do hot (leaving the key in the "on" position can damage a coil). To prove that it is vapor lock, you can check to see if your fuel is boiling. Use a clear section of tube in the fuel line before the carb, or, and this is what I was going to try, use a clear fuel filter.
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Old 07-02-2018, 01:13 PM Thread Starter
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@wolfeman haven't had a chance to bend up a line from the pump yet but that is the plan. Metal from the tank to the pump

@kenash do have a 1/4" insulator spacer; that's the thickest that'll fit under the hood w/ a 14" air cleaner

@NEFaurora will give that a try, I was wondering if maybe the tank isn't sufficiently vented

@quik I've got a clear filter in it so I can see it's definitely vapor lock; based on the minimal flow into the filter when it shuts off I'm guessing it's at the pump. Also I did have a coil related misfire earlier this year but I already replaced that

Thanks for the suggestions

I'm thinking the best solution (until I do EFI) is probably to put an electric pump back by the tank and maybe also re-do the lines from the tank to make them straighter; would that work? For the lines I put in last year I followed the stock path so there're several bends I could straighten out.


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Last edited by Ojenkins; 07-02-2018 at 01:17 PM.
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Old 07-02-2018, 01:33 PM
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Since my thoughts of coil getting to hot, carb spacer, fuel lines to close to block all touched on, only thing comes to mind then if no fuel in clear filter is get another fuel pump. Timing ok..

Only other small way to keep some of the heat out of engine bay is ceramic coat exhaust manifolds/headers.

I'm running a pretty stock 390 in my 67 in New England, 95 degree days no problem. Has a lot of heat. Note a turn signal hood on a 67/68, the vents on the hood are heat extractors. That helps

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Old 07-02-2018, 01:39 PM
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When you switch to a metal tube from the pump to the carb, consider using stainless steel. The heat transfer value is 1/3 that of steel. You could also use clear header paint, which is silicone ceramic based.


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Old 07-02-2018, 02:05 PM
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I had vapor lock a couple of years ago. I ended up with a 1" phenolic spacer under the carb and also covered the bottom side of the carburetor bowls with a heat reflective tape to help keep the heat away. That got me through a couple of summers until I switched to an electric fuel pump.



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Old 07-02-2018, 02:53 PM Thread Starter
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Thanks guys, sounds like an extra pump by the tank is probably what I'll go with. Will look into getting stainless for the pump - to - carb line; have also got some heat tape I might put on the line and or the carb bowls.

Headers are already ceramic-coated so under hood temps should be reasonable, seems it's just when the weather gets a bit too hot the mechanical pump isn't staying vapor-free.


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Old 07-02-2018, 08:28 PM
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do have a 1/4" insulator spacer; that's the thickest that'll fit under the hood w/ a 14" air cleaner
Try a shorter 14" air cleaner to fit a thicker spacer. May not fix your issue even with a thicker phenolic spacer. I've tried a few spacers (different thickness, materials) and still get vapor lock in hot weather if I park and come back too soon. It'll last for about a mile before it clears up. I have a FiTech EFI and not immune to the vapor lock.

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Old 07-02-2018, 10:38 PM
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1. Don't drill your fuel cap. If anything, in hot weather, you'll have excess PRESSURE in the tank, not suction. You don't want fumes escaping but you DO want fresh air entering.

2. Use MILD steel line from the pump to the carb. The problem with rubber (and any other line coating AND stainless) is that they don't RADIATE heat fast enough. It's not as much of an issue of the line ABSORBING heat as it is the line SHEDDING the heat. Once air gets moving the line will cool back down. Slow fuel flow at idle and hot temps will heat the line but a rubber line will HOLD the heat and won't let it go.

3. Get rid of your clear filter. If you have an Autolite carb use the factory metal screw-in filter. If you have an Edelbrock, use the banjo-style inlet with screw-on metal filter. If a Holley, use a Rochester inlet filter under the inlet adapter. Don't use any filter before the pump.

4.. Make sure the rubber line from chassis to pump and from tank to chassis isn't rotted on the inside and is stiff enough to not be collapsing, especially the one to the pump.

5. Run as much spark advance as you can without "pinging". If using distributor vacuum advance, switch to full manifold vacuum as a source. This will greatly reduce combustion temps in the exhaust and underhood heat (at the expense of some unburned hydrocarbons... a good trade-off as far as I'm concerned).
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Old 07-02-2018, 10:46 PM
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Quote:
Originally Posted by Ojenkins View Post
@wolfeman haven't had a chance to bend up a line from the pump yet but that is the plan. Metal from the tank to the pump

@kenash do have a 1/4" insulator spacer; that's the thickest that'll fit under the hood w/ a 14" air cleaner

@NEFaurora will give that a try, I was wondering if maybe the tank isn't sufficiently vented

@quik I've got a clear filter in it so I can see it's definitely vapor lock; based on the minimal flow into the filter when it shuts off I'm guessing it's at the pump. Also I did have a coil related misfire earlier this year but I already replaced that

Thanks for the suggestions

I'm thinking the best solution (until I do EFI) is probably to put an electric pump back by the tank and maybe also re-do the lines from the tank to make them straighter; would that work? For the lines I put in last year I followed the stock path so there're several bends I could straighten out.

Ok, 14" dia. does not translate to depth of the filter. I ran a 14" with a standard 3" thick filter and a 1/2" phenolic spacer. This was on a Eddy Performer RPM and a 1405 Eddy carb. Yes it was close, but it did "barely" clear my stock hood. One can also, install a "drop base" which allows additional clearance. I've been here done all of this......

KenA..
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333 Cu.in. T5z, 3:55, Dual 40 mm DCOE Webers
Performer RPM, CI cam, TFS/TWs, Tri-Ys, Discs w/Shelby Drums
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Old 07-02-2018, 11:03 PM
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Another ploy, install an electric Fuel pump. This is a classic fix for Vapor lock. But, not many, want to go through the additional funds to add one.....I did early on......

KenA..
64 1/2 Poppy Red Cvt. Resto-Mod
333 Cu.in. T5z, 3:55, Dual 40 mm DCOE Webers
Performer RPM, CI cam, TFS/TWs, Tri-Ys, Discs w/Shelby Drums
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Old 07-03-2018, 09:19 AM Thread Starter
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3. Get rid of your clear filter. If you have an Autolite carb use the factory metal screw-in filter. If you have an Edelbrock, use the banjo-style inlet with screw-on metal filter. If a Holley, use a Rochester inlet filter under the inlet adapter. Don't use any filter before the pump.
.
Thanks for those tips that's helpful; just wondering what is the reasoning for not running a clear filter? I have an Edelbrock.

Quote:
Originally Posted by kenash View Post
Ok, 14" dia. does not translate to depth of the filter. I ran a 14" with a standard 3" thick filter and a 1/2" phenolic spacer. This was on a Eddy Performer RPM and a 1405 Eddy carb. Yes it was close, but it did "barely" clear my stock hood. One can also, install a "drop base" which allows additional clearance. I've been here done all of this......
You're right, had forgotten about the option of a drop base for the filter. I have that same carb/intake combo, currently using an edelbrock insulator pad (https://www.amazon.com/Edelbrock-926.../dp/B00062YBPM) which is 0.320" thick. What would work better, the insulator pad or a 1/2" phenolic spacer? Obviously the spacer is thicker but not sure about relative thermal insulation properties.


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