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Hot gas? Vapor Lock?

Discussion in 'The Garage' started by Burt4x4, Jun 14, 2002.

  1. Burt4x4

    Burt4x4 3/4 ton status

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    So if a carbed 350 has hot gas and is getting vapor locked because of it What would the motor do?
    Or what are the symptoms of Vapor Lock?
    Loss of power? Motor dies or doesn't idel? Secondaries do nothing when floored?? etc.....????
    Thanks
     
  2. HarryH3

    HarryH3 1 ton status Author

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    The engine stops running. /forums/images/icons/shocked.gif When the fuel system vapor locks, the fuel in the supply line has gotten so hot that it turns into a gas instead of a liquid. The fuel pump isn't designed to suck those vapors so no fuel gets to your carb. /forums/images/icons/frown.gif Sometimes the fuel is just cool enough to get past the pump, but the carb is too hot, so the fuel boils in the float bowls. Either way, the result is that the fuel level in the float bowls drops below the jets and the engine stalls. /forums/images/icons/mad.gif

    An electric pump back near the tank can resolve the first issue. There are heat deflection plates you can install between the carb and the intake to help with the second. /forums/images/icons/cool.gif
     
  3. Burt4x4

    Burt4x4 3/4 ton status

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    OK well I'm not stalling out so I guess it's not Vapor Lock.
    What happen is on a road trip last week (hot day) my rig was running fine on the freeway. Then took another Hwy that heads up into the mountains and the first steep grade I came too my motor suddinly became super gutless and I had to hold the throttle just bairly with my foot.If I pushed to far on the throttle it would not do much more than sound worse.
    The next morining everything seam to run normal again? Well after it warmed up a bit. When it's cold and you start off down the road goin 20mph switchin gears the motor will stal.......BAM loud back fire under my rig. But in time after running the backfire & stal goes away???

    Any ideas????????
    Told my wife to get prepared for a new crate motor perchase /forums/images/icons/grin.gif /forums/images/icons/grin.gif That will fix it!! /forums/images/icons/laugh.gif /forums/images/icons/laugh.gif
     
  4. Chaz88K5

    Chaz88K5 1/2 ton status

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    i think your right...its time for a new motor...there is nothin you can do to save this one...it is also fedral law that you have to upgrade it to fuel injection...tell your wife that...it might work /forums/images/icons/grin.gif
     
  5. dogman

    dogman 1/2 ton status

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    Steve:
    Look at the fuel line route, can you see any rubber hose that is collapsed.
    (like a kink in a garden hose).
    vapor lock will do that to a thin hose.
    If bobbling fuel is not your problem, I'd check out the fuel filter first.
    Then I'd make sure that the choke is open, a stuck choke can really $crew with you.
    If all thats ok, make sure the float level is not dumping fuel in. check for pump pressure.
    then if that's not it, go get a new Holly. /forums/images/icons/grin.gif

    dogman
     
  6. BurbinOR

    BurbinOR 3/4 ton status

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    It can still be vapor lock and not stall.........when I lived in AZ my big block Camaro did that.........fixed it by putting in routing the rubber lines away from the headers........ Make sure your return lines have no restrictions. /forums/images/icons/laugh.gif
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    Great stuff!! Thanks!
    I'll double check the carb settings and choke linkage(hot stove type). May reroute the fuel line when I swap in the new pump and filters.
    Return lines? From the tank? Maby the gas tank ain't "breathing" so it's hard to 'suck' the gas out of the tank??
    Thanks
     
  8. Burt4x4

    Burt4x4 3/4 ton status

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    hahah Sounds good!!
    can you say 350RamJet ?? /forums/images/icons/cool.gif /forums/images/icons/cool.gif /forums/images/icons/cool.gif ya right 3500bucks.... /forums/images/icons/mad.gif
     
  9. BurbinOR

    BurbinOR 3/4 ton status

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    One other thought...........does your fuel pump even have a return line? Some early model Chev's did not, and that was part of my problem on the SS396 Camaro.
     
  10. Burt4x4

    Burt4x4 3/4 ton status

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    No. Only one line in and one line out.....
     
  11. BurbinOR

    BurbinOR 3/4 ton status

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    I'd say that is a big cause of it.......from my experience anyway. After I put a fuel pump with a return line on, the vapor lock was gone. Do you not have return lines to the tank?
     
  12. Burt4x4

    Burt4x4 3/4 ton status

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    I have 3 'vent' lines on the tank. Two go to a pipe in the rear corner and the 3rd follows the fuel line up to the engine bay into a round can that says Rochester on it. As for the fuel pump I don't recall any other lines besides the fuel inlet and outlet?? I will surly double check tonight!! Thing is though this fuel line setup has been the same sence I bought my K5 in 1993, that is when I put a new pump in, back in 93. So....???? Hell!Pss!Damn!
    hmmmmmm.... /forums/images/icons/confused.gif
     
  13. 91K5

    91K5 1/2 ton status

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    My first guess would be the carb. I'd do a compression check on the motor first to see if it's got some lazy valve springs or bad rings. The carbs float level might be low or high, it could have some wear on the jets/rods causing a bad A/F ratio, accelerator pump, or even a clogged fuel filter. A crate motors always fun to get, but you might be able to fix it with a carb rebuild or something else simple.
     
  14. BurbinOR

    BurbinOR 3/4 ton status

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    Sounds like you do not have a return line. My Camaro did but the PO put a non-return line pump on it..........thank goodness at the time my bud noticed it (GM Goodwrench mechanic), put the correct one on, hooked up the return line and problem solved. Might not be your problem, but not having a return line just doesn't sound right. That Camaro was a '71 by the way......... /forums/images/icons/tongue.gif
     
  15. Burt4x4

    Burt4x4 3/4 ton status

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    Hmmmm Sounds like a question for the first gen board, on the return line deal. I am the 3rd owner of this K5 so everthing is still perrty much there. I will look for unused return type lines and try to find out what my setup should have.
    I will go thru the whole fuel system this weekend. I'll reset the float and A/F mix check timming toss in that fuel pump & filters.
    Thanks!!
     
  16. dogman

    dogman 1/2 ton status

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    You know if you put the same carb and dist. on a new crate motor.
    Then If you still have that problem, you will know its not the motor.
    I had a HEI chip that would only screw up when the temp outside was around 90deg.
    cool down it runs, then would return like i was out of gas.
    and I thought it was vapor lock too.
    history tells me: the cheapest thing to fix and most often will solve the problem.
    change the carb fuel filter. They will clog and should be changed at every tune up.

    dogman
     
  17. muddin4fun

    muddin4fun 3/4 ton status

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    I thought only the newer models (efi) had return lines for fuel /forums/images/icons/confused.gif
     
  18. txbluethunder

    txbluethunder 1/2 ton status

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    nope...my 86 has fuel return lines
     
  19. BurbinOR

    BurbinOR 3/4 ton status

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    My 79 has them.......... /forums/images/icons/tongue.gif
     
  20. behemoth

    behemoth 1/2 ton status

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    Correct me if I'm wrong, but from what I'm reading into this is - if you keep the engine (and
    engine compartment) relatively cool, you'll eliminate any kind of fuel evaporation - and therefore,
    stall onditions related to lack of liquidfied fuel to the carb.

    My question is - how does a TBI play into this scenerio? I'm a 'carb' idiot, so a TBI is star trek
    to me! I had the same symptoms a few weeks ago - I stalled out at a red light and it was a
    hot day and a lot of stop and go traffic. The temp gauge pegged a few minutes later. I've since
    replaced the thermostat (170 degree - I know - it's too low. I'll replace it with a stock 190 this
    weekend) and radiator cap. I'm still running 'warm', but no more stalls. Pick-up seems sluggish,
    though - not the 'pep' it had before.

    Any thoughts?
     

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