Vapor lock

[charlie D]

My car sat for many years and only had occasional starts and short drives. This past year I used it more and experienced vapor lock. Only happened after I had driven maybe 20-30 minutes. I have read somewhere on this forum that the alcohol blended fuel boils at a lower temp causing these cars to be prone to vapor lock. So while I am working on it this winter it might be a good time to do what I can to prevent vapor lock. The fuel lines are away from the block and the fuel log is offset from the block. I can easily insulate those, but I suspect the fuel actually boils in the carbs. Has anyone used the spacer blocks sold to isolate the carbs from heat? What have your experiences been with vapor lock and what did you do to cure it? Thanks.
Charlie D

[vtgt500]

Charlie, this has been beat to death on every auto enthusiast forum since Gore invented the internet.  Need to differentiate between vapor lock and flooding due to fuel bowl peculation.  With a dual quad FE and tube headers, under hood heat in traffic is an issue.  My solution was, 1/2" thick phenolic spacers, and a race fan.  Fan is ridged designed to move a LOT of air.  Type intended for use in short track, modified cars.

[Bob Gaines]

Charlie, this has been beat to death on every auto enthusiast forum since Gore invented the internet.  Need to differentiate between vapor lock and flooding due to fuel bowl peculation.  With a dual quad FE and tube headers, under hood heat in traffic is an issue.  My solution was, 1/2" thick phenolic spacers, and a race fan.  Fan is ridged designed to move a LOT of air.  Type intended for use in short track, modified cars.

To add to this excellent observation -don't forget the fuel log . The fuel log is bolted to the intake . The tabs bolted to the intake help turn the fuel in the fuel log into a boiling pot.The tabs are a conduit for heat from the block.  I had some success by cutting the tabs off of the fuel log (only do this to a repro fuel log) and allowing the two rubber fuel lines and the metal fuel line hold the fuel line.  The suspended fuel log was perfectly secured using this method.. The fuel pump is another source of heating the fuel . In some extreme cases the mechanical fuelpump is by passed by means of a electric fuel pump mounted in another location typically the trunk.Another location can be where the fuel line passes through the engine compartment apron.  The pump is employed to completely isolate the fuel line from the hot engine block. You may have to use some or all of these suggestions .

[Bob Gaines]

Charlie, this has been beat to death on every auto enthusiast forum since Gore invented the internet.  Need to differentiate between vapor lock and flooding due to fuel bowl peculation.  With a dual quad FE and tube headers, under hood heat in traffic is an issue.  My solution was, 1/2" thick phenolic spacers, and a race fan.  Fan is ridged designed to move a LOT of air.  Type intended for use in short track, modified cars.

To add to this excellent observation -don't forget the fuel log . The fuel log is bolted to the intake . The tabs bolted to the intake help turn the fuel in the fuel log into a boiling pot.The tabs are a conduit for heat from the block. I had some success by cutting the tabs off of the fuel log (only do this to a repro fuel log) and allowing the two rubber fuel lines and the metal fuel line hold the fuel line.  The suspended fuel log was perfectly secured using this method.. The fuel pump is another source of heating the fuel . In some extreme cases the mechanical fuelpump is by passed by means of a electric fuel pump mounted in another location typically the trunk.Another location can be where the fuel line passes through the engine compartment apron.  The pump is employed to completely isolate the fuel line from the hot engine block. You may have to use some or all of these suggestions .

You can tell a repro fuel log from a genuine version by the way the taps are secured to the log. Repro tabs are welded across the top of the tab as it touches the log. Original fuel logs have the tabs spot welded to the log. You will not see the weld line on the top of the tab but will see two spot weld marks on the back side of the tab where it rolls over at the top and connects to the log.

[Bill]

My car sat for many years and only had occasional starts and short drives. This past year I used it more and experienced vapor lock. Only happened after I had driven maybe 20-30 minutes. I have read somewhere on this forum that the alcohol blended fuel boils at a lower temp causing these cars to be prone to vapor lock. So while I am working on it this winter it might be a good time to do what I can to prevent vapor lock. The fuel lines are away from the block and the fuel log is offset from the block. I can easily insulate those, but I suspect the fuel actually boils in the carbs. Has anyone used the spacer blocks sold to isolate the carbs from heat? What have your experiences been with vapor lock and what did you do to cure it? Thanks.
Charlie D

Look at the Mr Gasket 3710 heat shield kit. I used the two smaller heat shields sandwiched between a gasket on my old 427 2X4 Tunnelport powered Cobra kit car. Had issues similar to yours in the hot, high humidity, stop and go traffic of the northeast. Once I put the heat shields in, all of those issues went away. It really is that simple a solution.

Bill S.

[Tom Honegger]

I had the same issue on my 289 Shelby GT 350. Died a couple times in traffic on a car show/cruise-in. After it cooled off, started right up. I didn't add an extra cooling fan, just a spacer and new gaskets between spacer and carb and manifold. Solved the problem. I even got stuck in freeway traffic on the way home from SAAC convention in Indy a couple years ago. Temp gauge kept going up, but never stalled out. My fuel line from inner fender well to carb is a rubber line (not original, obviously) that doesn't clamp to engine anywhere, so no direct engine heat to fuel line.
Also, look for alcohol -free gas in your area. We have Casey's General Store chain that sells no alcohol premium.

[1967 eight barrel]

There is no need for an electric fan. I will try and put you a list of products by part number together. I bought the Canton 1/4" spacers for the carbs and the 1/8" spacers for the fuel log. It insulates it for the most part from the intake. I also have the heater hoses running in close proximity to the fuel log. I used a portion of insulation at the rear where it comes up from the firewall and sits against the fuel log. That cured the issue. The only other item I am running is the 406/427 Canister fuel filter. I am in the Dallas area and it is well over 100 here during the summer.

                                                                                    -Keith

[2112]

Anyone blocking off the EGR passage In the manifold?

[1967 eight barrel]

Yes. I used the Fel Pro 1246 S3. They have a metal shim core. They block the manifold crossover and the metal core will assure they aren't burnt through like paper gaskets.

                                                         -Keith

[shelbydoug]

Yes. I used the Fel Pro 1246 S3. They have a metal shim core. They block the manifold crossover and the metal core will assure they aren't burnt through like paper gaskets.

                                                         -Keith

I like to block them too but it absolutely eliminates the possibility of driving the car under about 30 degrees. The carbs will ice up. You can run the car in the driveway, etc., but don't take it for a long ride. It's done until it warms up again.

[69 GT350 Vert]

Holley Sniper EFI system is the ultimate solution if you want to drive your car a lot in the summer heat.  It will cold start like your daily driver, no more flooding/fuel smell after hot shut off, and a perfect air/fuel ratio all of the time.  Plugs will never foul again. 

https://www.holley.com/products/fuel_systems/fuel_injection/sniper_efi/sniper_4bbl_tbi_kits/

[Cobrask8]

Bill beat me to the heatshield, as I had this on both my 428SCJ and the FFR race car. Get everything off the manifold, and the heat shield helps. Yes, does not look stock, but if you can't drive it, then what fun is it?

Other easy fix is the fuel pump. I bet you still have an old original, and they do get tired, check balls in the check valves no longer fit well. Replace.

Ultimate fix is a hidden electric pump out back.

[1967 eight barrel]

Yes. I used the Fel Pro 1246 S3. They have a metal shim core. They block the manifold crossover and the metal core will assure they aren't burnt through like paper gaskets.

                                                         -Keith

I like to block them too but it absolutely eliminates the possibility of driving the car under about 30 degrees. The carbs will ice up. You can run the car in the driveway, etc., but don't take it for a long ride. It's done until it warms up again.

You're in Hell....... I mean New York. I just got out of Ithica. Too cold to close them off if you want to drive the vehicle  fall to early spring. I froze my arse off.

[shelbydoug]

Yes. I used the Fel Pro 1246 S3. They have a metal shim core. They block the manifold crossover and the metal core will assure they aren't burnt through like paper gaskets.

                                                         -Keith

I like to block them too but it absolutely eliminates the possibility of driving the car under about 30 degrees. The carbs will ice up. You can run the car in the driveway, etc., but don't take it for a long ride. It's done until it warms up again.

You're in Hell....... I mean New York. I just got out of Ithica. Too cold to close them off if you want to drive the vehicle  fall to early spring. I froze my arse off.

Well, it won't overheat. 

[charlie D]

Thanks, great conversation guys. I will be doing the carb spacers and isolate the fuel log as well. Seems as though that worked for Kieth in 100 degree Texas, so it should do me OK in 98 degree Maryland. Why didn't I think to check the mechanical fuel pump, good idea! I do have an electric fuel pump that I originally switched from the dash, but moved it to a micro switch on the carb linkage so it only kicks in at full throttle. Not much help in that configuration for vapor lock. I will move it back to the dash. Thought about changing the whole induction system, but even though I am not into strict restoration/preservation, to me the dual quads are part of the character of the 67 GT500. If I were to do anything there, it would be to save the original system for the next owner and install a more modern, maybe smaller CFM, dual quad set up.

Hey Keith, if you can find those part numbers, it would be a big help.

Thanks again to all,
Charlie D