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  • Could it be vapor lock?

    Sadly today was this first time Roscoe was out. Took me to the carwash to remove the dust. Started with barely tapping the starter and purred like a kitten.This was the first time with new in tank filter, new gas shut off valve, Wix filter, new bowl to carb gas line and new Renner jets. So ran wonderful on the ride to and from the car wash until I got stuck by a train. I shut him down until the train passed and it started acting up. trying to die, coughing and sputtering with an occasional back fire.
    Once I limped into my drive I immediately raised the hood and noticed an air space in the top of the sediment bowl and tiny bubbles active. I pulled the gas cap while driving so its not a vacuum issue. Is this a sign of vapor lock and if so how do I prevent it?

  • #2
    I wrapped my fuel lines in thermotech insulated wrap to keep the fuel lines from firewall to carburetor cool as they have a tendency to overheat due to there proximity to the exhaust since then I have not had any issues.16AC12A7-6967-4B63-873A-914943F8E794.jpeg

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    • #3
      Try tightening the thumb nut on the bottom of the sediment bowl. Sounds like it is sucking air.
      You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!

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      • #4
        Check the cap anyway. Flip it over and make sure the vent hole is not obstructed by the gasket
        3 ~ Tudor's
        Henry Ford said
        "It's all nuts and bolts"


        Mitch's Auto Service ctr

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        • #5
          I will try both the items mentioned. Would the sucking air issue cause an air space in the top of the bowl?

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          • #6
            Originally posted by Big guy View Post
            Would the sucking air issue cause an air space in the top of the bowl?
            Ayup! Just like sucking through a straw with a hole in it. Dead give away.
            You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!

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            • #7
              'Vapor Lock' to me is not having gas. That was not your problem.

              On a nice warm day you cruised to the car wash, once all nice & pretty cruised on home only to be stopped to watch a train pass by. With the engine shut down, all that engine heat under the hood traveled to your carburetor, boiling the gas in the fuel bowl, basically flooding the engine with rich fuel. That was the hard start & rough running until burned off.

              Summer months you have two options. In the exact same situation shut off the fuel valve and let the engine run until the carburetor is dry. After 'your train has passed', open the valve & re-start.
              Second option that some have success with is with each fill up, add 3 oz's of diesel or MMO. My
              guess is that both might raise the gas's boiling point ??

              Experiment....and Enjoy the Ride.

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              • #8
                Good advice above.

                Another thing is to make sure the fuel line from sediment bowl to carburetor is pointed downhill. Many aren't. If its not the whole way just 'warp' the line until it is.

                I also made a light sheet metal shield bolted to fit under the manifold and exhaust pipe.

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                • #9
                  Big Guy I have seen this happen countless times on club tours. The exact same conditions. Stop the engine for a few minutes and the trouble begins when re-starting. When the ambient temp. gets to about 85 is when it begins to occur. Never in the winter. We have tried every thing imaginable including additives, diesel, etc. Those things may work temporarily but the problem will come back with the right conditions. The best thing we have found to stop it is ethanol free gas. Have never had it happen when using that. My brother and I drove a 31 Coupe off over Dallas back in the late 40's and 50's and vapor lock never occurred even the summer time. Some say it is partly attributed to the seasonal mix of the fuel.

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                  • #10
                    The talk about the fuel itself is a good one. That can make a difference, the ethanol stuff is crap. So, adding some kerosene, diesel does seem to help. I use the ethanol crap but mine gets all the old stale gas from the boat, weedeater, lawnmowers, etc and it runs fine, it really doesn't care what I feed it. I think the oil in the fuel has something to do with it.

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                    • #11
                      The Model A engine was designed with the lowly compression ratio of 4.5 to 1 for the reason that era fuel quality varied so much between dealers. I suspect today's 87 octane would be considered 'the good stuff'.

                      Sometime in 1929 the Model A carburetor had a vent hole added over the fuel bowl. This helped boiling gas vapors to escape outside of the engine in stead of flooding it.
                      Since most Model A carburetors are restored from a collection of parts, this vent hole might be worth checking for.

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                      • #12
                        Here is a post I put together on the vent hole that JB speaks of. You need to have matching housings for it to work
                        https://www.vintagefordforum.com/for...=3131#post3131
                        3 ~ Tudor's
                        Henry Ford said
                        "It's all nuts and bolts"


                        Mitch's Auto Service ctr

                        Comment


                        • #13
                          Thanks guys, I have shielded the fuel line and tightened the sed bowl glass.Cleaned the fuel cap vent. I still need to look for those vent holes in the Zenith. Going to be very warm tomorrow so I'll do some test driving. Ethanol free isn't easy to find. The marinas have it but they are set up dock side. With the low consumption this year, it would not surprise me that we are still getting winter blend fuel which has way more light ends. I'll keep you posted.

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                          • #14
                            Originally posted by Big guy View Post
                            Thanks guys, I have shielded the fuel line and tightened the sed bowl glass.Cleaned the fuel cap vent. I still need to look for those vent holes in the Zenith. Going to be very warm tomorrow so I'll do some test driving. Ethanol free isn't easy to find. The marinas have it but they are set up dock side. With the low consumption this year, it would not surprise me that we are still getting winter blend fuel which has way more light ends. I'll keep you posted.
                            Some of teh major gas station's premium gas is supposed to be ethanol free. BP, Shell, Kwik Trip, usually has it. Usually it is marked as ethanol free on the pump.

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                            • #15
                              Well guys, I am officially bummed out now. I have finally been able to take another ride. Running very well until I made a couple stops. I turned the gas off and ran it a bit both times. Five minutes later the same symptoms returned. No power, sputtering and an occasional backfire. Made it home, lifted the hood and there was that vapor space in the sediment bowl again. I love this car but it should be driven.

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                              • #16
                                Originally posted by Big guy View Post
                                Well guys, I am officially bummed out now. I have finally been able to take another ride. Running very well until I made a couple stops. I turned the gas off and ran it a bit both times. Five minutes later the same symptoms returned. No power, sputtering and an occasional backfire. Made it home, lifted the hood and there was that vapor space in the sediment bowl again. I love this car but it should be driven.
                                I still say that if there is an air gap in the glass bowl, there is a leak either around the gasket or the fitting or even a crack somewhere around the bowl.
                                You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!

                                Comment


                                • #17
                                  Maybe pop out the Wix filter and retest. We all use it with no issues, but lets change something
                                  3 ~ Tudor's
                                  Henry Ford said
                                  "It's all nuts and bolts"


                                  Mitch's Auto Service ctr

                                  Comment


                                  • #18
                                    Bummed,

                                    Yes your car needs to be driven & enjoyed......obliviously a 'keeper ' because she always brings you home.

                                    I'd suggest you take the same route and this time no stops.

                                    IF you get the same symptoms, maybe you have a failing condenser or coil. An A&L burnout proof condenser is inexpensive and you should be carrying a spare.

                                    I'd borrow a know good coil from a buddy and try that as well.

                                    Try these steps one at a time...it's a simple car with simple fixes.

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                                    • #19
                                      I am leaning towards the cap vent. When it acts up, remove or loosen the cap. Do you hear a "hissing" sound from around the cap? If so....
                                      I had this happen twelve miles away from home and loosening the cap solved the immediate issue. Finished my trip and returned home with nothing but a rattling gas cap.
                                      Cleaning the vent hole and even adding an additional one corrected the problem for me... Chap

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                                      • #20
                                        Originally posted by Mitch View Post
                                        Maybe pop out the Wix filter and retest. We all use it with no issues, but lets change something
                                        Pop out the Wix filter and if you have the brass screen remove it also, your tank screen should take care of rust out of your tank. Make sure all of the fuel lines are going down hill towards the carburetor !!! Gravity flow fuel system.

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                                        • #21
                                          So I may have corrected the issue thanks to you guys. I removed the Wix filter and removed the new gas line, shortened it and bent it so it would slope down the entire length. I took my drive and tried to duplicate the issues. So far so good.

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                                          • #22
                                            I have the filter/screen, and do not have problems. Try them again, most likely the issue was the gas line.

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                                            • #23
                                              Watch that ferrule!!!! And yes no problems with the Wix, but drive it for now as is, to confirm. Then reinstall.. The slope and or ferrule positioning, may be the culprit
                                              https://www.vintagefordforum.com/for...1019#post11019
                                              3 ~ Tudor's
                                              Henry Ford said
                                              "It's all nuts and bolts"


                                              Mitch's Auto Service ctr

                                              Comment

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