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1955 V8 won't start
 
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1955 V8 won't start

 
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 Wayne N Barwick
(@wayne-n-barwick)
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Joined: 42 years ago
Posts: 2
Topic starter April 10, 2024 5:22 pm  

My '55 with a 283 V8 won't start unless you pour some gas down the 2 barrel carb.Once it starts, it runs fine.Leave it overnight, won't start next day.Tried 2 carbs-same result.Choke seems to set OK when gas pedal pressed.Someone said maybe no vacuum.I have a gauge on all the time and vacuum runs at 20 on idle.Help!!

 


   
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 Dennis Christianson
(@dennis-christianson)
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Joined: 20 years ago
Posts: 13
April 10, 2024 5:59 pm  

Sounds like a fuel pump that needs higher rpm before it will build any pressure. I would check pressure and volume after it has set overnight.


   
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 Wayne N Barwick
(@wayne-n-barwick)
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Topic starter April 10, 2024 6:08 pm  

@dennis-christianson I'll give that a shot.Thanks.


   
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 William J Anderson
(@william-j-anderson)
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Joined: 14 years ago
Posts: 6
January 1, 2025 2:35 pm  
Same symptoms as I have with my '56 2 BBL. only I installed an external check valve ahead of the fuel pump to keep the fuel from back flowing from the pump to the tank.
My next approach would be to adjust the carb bowl vent to closed, with throttle closed, and see how the system reacts.  If you look closely, the bowl vent is located on the top of the carburetor, on the front left side, controlled by throttle linkage.  It is a rubber flap attached to a spring steel support.
I think the problem would then be a rich hot soak issue due to perculation of fuel thru the main (boost venturi) discharge system.  The bowl vent exists to prevent the rich hot start problem by allowing the fuel vapor to exit the float bowl, which, in turn, allows the fuel to evaporate overnight.
To combat that, I think insulating the carb by changing gasket to either phenolic (thicker insulator) or insulating gasket material with foil tape added to each side of the gasket. Shiny surface of the tape rejects heat transfer.  Being that the air cleaner is so large, and oil bath, I don't think the primary loss of fuel (vapor) is through the air cleaner.  Beyond that, running a colder T-Stat or no stat could reduce the under hood temp running and at shut down.  One other approach would be to come up with a fan with more blades or one that moves more air to further cool the underhood.  Also, stay away from Ethanol fuels.  Ethanol is used primarily in 3 seasons.  Not summer.  Adding 10 to 15% ethanol to regular gasoline increases vapor pressure, and improves startability in cold weather, which can contribute to vapor lock under warm conditions.
 
One other heat source is that these cars have a heat riser bi-metal valve in right side exhaust manifold to get hot exhaust to flow from one bank to the other thru a passage under the floor of the intake.  That heat is to improve fuel vaporization, help cold weather drive ability, and minimize tendency toward carburetor icing.  Blocking the heat riser open is a quick band-aid, but the better solution is intake gaskets with the passage blocked off.  A good TIG welder could weld a patch over the passage if the gasket is steel.  Otherwise, if the car has paper gaskets, you modify a stock paper gasket or make your own.
 
Or, like some folks do:  Install an electric booster pump ahead of the mechanical pump with a momentary push button to allow priming the system during starts.  The mechanical pump will draw gas thru the electric pump even if the electric pump is not running.  Electric pumps can be a hazard if hard wired to the ignition key.  Somehow, someday, someone turns ignition key on when the fuel line is open and a shower occurs, enhancing the possibility of a "thermal" event.
This post was modified 2 weeks ago by William J Anderson

   
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skidplate
 skidplate
(@skidplate)
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Posts: 27
January 1, 2025 10:47 pm  

You could just do a real quick electric fuel pump splice in and see if that fixes it. You can get them for whatever psi you need. That'd tell you a lot.


   
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 William J Anderson
(@william-j-anderson)
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Joined: 14 years ago
Posts: 6
January 2, 2025 3:39 pm  

I'm putting my money on lack of fuel due to evaporation.  If I spray starting fluid (mostly ether) into my air cleaner, I get an almost instantaneous first fire which does not always carry over to running without a re-crank, since the carb still isn't full enough.  Then after running, the designers of that fuel system rely on the choke blade to blow/suck open to lean out the mixture while the bi-metal coil slowly opens the blade during warm-up..  On my ride, I haven't established the delicate balance between blade opening to support clean combustion vs having it load up/soot foul the spark plugs due to over rich condition.  By the 70's carbs had a vacuum choke pull off linkage to crack open the choke blade immediately after start-up, which eliminated the problem and reduced tailpipe emissions.


   
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