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Technical Starting issue... odd.

Discussion in 'Traditional Hot Rods' started by AGELE55, Aug 10, 2021.

  1. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    350 SBC 300HP. Flat tappet , bone stock crate engine. 750 cfm edlebrock.
    Yes, I know I'm over carburated, but I'm saving my green stamps for a 650 cfm. The 750 came off the engine I thrashed.
    Starts with a tap of the key when cold, or within 5 minutes of shutdown. No gas pedal required.
    After sitting a bit, it wont fire without excessive cranking. So far it seems like just flooring the pedal works best, with it firing up after 3-5 seconds.
    Or wait an hour or so and boom, fires right up.
    I have a fuel pressure gauge and a mechanical fuel pump. I see 6-9 psi holding for hours after shutdown, so I know its not draining back away from the bowl.
    Ok...ready, set, go. Fix me up boys.
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 50,172

    squirrel
    Member

    Likely just fuel boiling in the carb, flooding the engine....see about some insulation (carb spacer? heat shield?) between the intake and carb. Or get used to holding the throttle open for hot starts.
     
    Tutashen and AGELE55 like this.
  3. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    Odd...never had the issue with the old engine and I'm using the same intake and carb. I'll try a mycarta spacer and see what that yields
     
  4. carbking
    Joined: Dec 20, 2008
    Posts: 3,193

    carbking
    Member


  5. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,584

    Elcohaulic
    Member

    Flooding.. Need a 1/4" return line from the supply side of the fuel pump to the tank.. A return line makes a real pain in the ass your best friend..
     
    Rramjet1 likes this.
  6. gary macdonald
    Joined: Jan 18, 2021
    Posts: 181

    gary macdonald
    Member

    Fuel boiling ( corn fuel ? ) or the carb has a internal leak . Your pressure gauge wont show a spare 1/2 bowl of fuel . Did you have an electric fuel pump on your thrasher motor with this carb ?
     
  7. You answered your own question ,,,,actually Squirrel did ,,,,,it’s a flooding situation .

    The symptoms you are experiencing,,,,,and the things you are doing to overcome it .
    If you have to floor the pedal to start it,,,,,,it’s flooded .
    9 psi of pressure is at the top range,,,,,actually a little over the top in my book .
    And like someone else suggested,,,,a return line is not a bad idea .

    Tommy
     
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  8. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

  9. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    Nope, always mech fuel pump.
     
  10. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    Not sure how to go about plumbing in a return line on a mechanical fuel pump...
    Is the intent to bleed off pressure?
     
  11. Try the carb spacer first,,,it’s a lot easier then plumbing a return line .
    However,,,,,your pressure is max,,,,,check it closely .
    You might could just lower the pressure and fix your problem ?
    Either way,,,,the pressure is too high in my opinion .

    Tommy
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 50,172

    squirrel
    Member

    There are a couple ways to do the return line...one is to get a pump that was made to use a return line, they were pretty common on Chevys starting in the 70s. Or you could use a filter with a return line fitting built in, mount it near the carb, like a 33041 if you have 3/8" line, or 33040 if you have 5/16".

    either way you have to figure out how to connect a return line at the tank, such as by adding a 1/4 tube soldered into a hole in the sender unit, or something.
     
    carbking and Desoto291Hemi like this.
  13. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    I’ll go with a spacer for now and see how that works. Oddly enough, I’ve been threatening to drop the gas tank and install a vent line from the top of the tank to the filler neck. I’m tired of getting a gas bath when standing too close to the fill door. It BURPS gas before the nozzle can react and shut off.
    If I do that mod, maybe I’ll plumb in a return line while I’m in there.
     
    Desoto291Hemi likes this.
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 50,172

    squirrel
    Member

    The 57 tank has a vent line for the filler, but the 55 neck needs to have the vent added to the top of it.
     
    427 sleeper likes this.
  15. carbking
    Joined: Dec 20, 2008
    Posts: 3,193

    carbking
    Member

    No, the spacer will not change the hard start hot issue, but it may (or may not) help with hot idle issues while running.

    The key in the link is to totally forget EVERYTHING you have been taught on pressing the footfeed to the floor to start a hot engine. The gas is so volatile the engine never (or takes a long time) catches up to the vapors.

    By NOT touching the footfeed, you shut off the supply of vapors to the intake, allowing the engine to pump out the overrich mixture.

    Try it, it won't cost you anything either in parts or labor; and it works!

    A return line will help, but may not completely solve the issue without changing your starting routine.

    Jon.
     
    pprather likes this.
  16. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    Appreciate the input...however...there's got to be a way to not crank for 5 seconds when hot. Whats the trick?
     
    31Vicky with a hemi likes this.
  17. Run the non ethanol fuel.
    Hot engine with shit for fuel, a successful start after 5 seconds isn’t bad.
    As to your other remarks that this didn’t happen on your other engine last year,,, fuel out of the pump changes.
    Fuel evaporates, percolates, and goes stale faster than ever.
     
  18. AGELE55
    Joined: Jan 4, 2018
    Posts: 394

    AGELE55
    Member

    I’d have better luck finding Jimmy Hoffa buried in Amelia Earhart’s plane than finding non ethanol gas out here in the sticks...
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 50,172

    squirrel
    Member

    wait until it cools off?

    I've had fewer problems with hot starts with 91 than with 87, on a couple cars. Might or might not help you,.
     
    AGELE55 likes this.
  20. Your Edelbrock should see 4-5 pounds fuel pressure, maximum. You have a pressure gauge, do you have a pressure regulator?

    Anyway, with hot start, as @carbking said above, do not touch the gas pedal until the engine fires and you are ready to stop cranking. Touching it during cranking will cause flooding.
     
    Desoto291Hemi likes this.
  21. Greg Rogers
    Joined: Oct 11, 2016
    Posts: 486

    Greg Rogers
    Member

     
  22. Several people have pointed to the high fuel pressure, yet this is ignored in responses. Why? It is easy to lower the pressure to a more acceptable (to the carb) level, so why not? If you don't have an adjustable fuel pressure regulator, you know what to do.
     
    AGELE55, dirty old man and pprather like this.
  23. Tutashen
    Joined: Aug 8, 2015
    Posts: 86

    Tutashen

    the fuel pumps with return lines were for emissions the vapours were routed into a charcoal canister back to the tank, i don't think that's the issue, i think when your intake was put on whomever didn't use those little square things to block off the heat risers under the intake so the carb is boiling , take your intake off an check , if they aren't there you have hot coolant heating your intake manifold an if you aren't living in the north pole you don't really want that :)
     
  24. No trick. Just not HAMB friendly. DITCH THE CARBURATOR! I have done so and would not change back for anything.

    Ben
     

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