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Back fire

Discussion in 'The Hokey Ass Message Board' started by Ford1948f1, Jun 9, 2013.

  1. Ford1948f1
    Joined: Apr 8, 2013
    Posts: 10

    Ford1948f1
    Member
    from Corona

    Hello I Have a 1940 dodge pickup with a inline 6 and it back fires threw the carburetor. I have rebuild the carburetor and check my timing and everything seem ok. What else could cause this if any one could help me. Thanks in advance.
     
  2. Do a compression check and leakdow to check for stuck or chipped valves. Stretched timing chain?
     
  3. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,385

    landseaandair
    Member
    from phoenix

    If it ran the same before touching the carb, accelerator pump is working, firing order and timing look correct, a compression check might be in order to prevent you chasing your tail. Once major mechanical issues are sorted out (possible stuck or bent valves, blown head gasket, etc.), you can go deeper into fuel and ignition.
     
  4. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,385

    landseaandair
    Member
    from phoenix

    Beat me to it.
     
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  5. Ford1948f1
    Joined: Apr 8, 2013
    Posts: 10

    Ford1948f1
    Member
    from Corona

    I was afraid of the valves I think this could be my issue. it ran fine and just stared to do this. Could valve clearness do this to.
     
  6. big M
    Joined: Mar 22, 2010
    Posts: 709

    big M
    Member

    If you have an intake valve too tight, it can, indeed backfire through the carb. Another thing to check is that you haven't6 crossed a couple of plug wires [firing order]

    ---John
     
  7. greasemunkey
    Joined: Jul 24, 2007
    Posts: 201

    greasemunkey
    Member
    from katy, TX

    I've had the same issue if the distributor is in 180 degrees backwards...
     
  8. junk yard kid
    Joined: Nov 11, 2007
    Posts: 2,714

    junk yard kid
    Member

    Or if your dwell is way off.
     
  9. waterhorse
    Joined: Oct 17, 2008
    Posts: 138

    waterhorse
    Member

    Like has been said, double check the plug wires at the distributor. I'm thinking out loud but, if engine has not run in a while it could be an intake valve sticking partially open. You can pull the tin side covers and look at the valve train while it's running.
    Let us know what you find.
    Greg
     
  10. Ford1948f1
    Joined: Apr 8, 2013
    Posts: 10

    Ford1948f1
    Member
    from Corona

    The distributor can only go in one way.
     
  11. Ford1948f1
    Joined: Apr 8, 2013
    Posts: 10

    Ford1948f1
    Member
    from Corona

    Took the truck out today and it back fires more under load, more in 2nd gear.
     
  12. MO_JUNK
    Joined: Jan 22, 2006
    Posts: 1,012

    MO_JUNK
    Member
    from Rolla, Mo.

    Is your cam going flat? Are you using a Zinc additive in your oil.
     
  13. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    Compression check as stated, and check points / dwell....

    I had an L-6. 230. If I remember, the distributer can go in 180 off...

    I doubt its caused by a lack of zink additive, but hay...LoL
     
  14. BootleggerMatt
    Joined: Aug 17, 2011
    Posts: 258

    BootleggerMatt
    Member

    That's not what being 180 out means, it means the distributor was installed with the motor at top dead center on the exhaust stroke rather than the compression stroke. If the engine ran before and you never pulled the distributor I wouldn't worry about it. If it always ran crappy I would verify your distributor is pointing to the right plug wire at top dead center on compression stroke.
     
  15. BS -
    So much BS that I have $100.00 that say the engine will not run when it's firing on cam overlap.

    Backfire thru carb causes
    Too Lean but these are sporadic and "can appear " to effect any cylinder in the order .

    Firing when intake valve is open due to internal mechanical issues or ignition wires crossed.
     
  16. I'd certainly pull the plugs and look for a lean condition.
     
  17. Cams in that time period hardly ever went bad like the later ones do so....I discount that.
    Id bet since you say it was a recent development and had been running good ,it is this....
    Older cars by nature either sat a period of time before we start driving em or they set as we don't drive them daily for the most part.
    When the set carbon will sometimescome loose when they are run after setting and get stuck in the partially open valve,hence causing bad seal on your intake valve to its seat.....
    pour water in a spray bottle and while revving your engine,spray the water in the open carb till it dies out.....repat about a dozen times and see if the problem goes away.....worth a try.
     
  18. Had a similar experience some years ago with a flathead 6 in a 50s Dodge p/u. Started good, idled, and ran OK cold but picked up an intake backfire after it warmed up. Compression test at operating temps turned up a weak cylinder. Pulling the head revealed a slightly burned intake valve and some weak springs.

    Burned intake seemed odd to me but was advised that this was probably the result of adjusting the lash just a bit too tight or with the engine not up to full operating temperature.

    After making the repairs we adjusted the lash just a couple thousandths looser than the stock specs just to be safe. Still ran surprisingly quiet, especially with the side covers back on and the hood closed.
     
  19. Fortunateson
    Joined: Apr 30, 2012
    Posts: 2,693

    Fortunateson
    Member

  20. While the engine is running feed a qt. of ATF down the carb while running at high idle and see if that helps,damn thing is gonna smoke but will clear up. You might have carbon on valves and this will clean them up!
     

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