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Intermittant back fire

Discussion in 'The Hokey Ass Message Board' started by plym_46, Jul 31, 2012.

  1. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    So on my Studie, after it starts and runs for a few minutes (fairly quick start then decent idle) it begins to intemittently backfire sounds like the exhaust side, this seem to come from both cylinder banks, in a random cycle. It will idle nice and smooth, the spit once, once or twice or two or three time, then settle into a smooth idle again. I believe it exhaust side but my ears ain't what they were and it could be carb back fire, I am running with the aircleaner on.

    Changing the timing by rotating the dist has no effect. I am thinking it may be exhaust valves hanging up, but it would seem this would be a cold symptom and go away as the engine warms, but its seems to be the opposite.

    Not there when cold, appearing when warmed. It runs smoothly off idle and does not seem to missfire at mid level rpms.

    When I last did a compression check, all cylinders were at 110 lb. + or - 5 lbs dry. Thought this was good so I did not do a wet test.

    Thought maybe spark plug wires crossing or leaking but at night running shows no tell tail arching.

    Can't find my vacuum gauge but there doesn't seem to be any audible vacuums leaks, and all ports are accounted for.

    So is this one of those electrical problems that will be fixed by fiddling with the carb, or one of those fuel problems that will require electical parts??

    Just replaced the electric fuel pump with a 7lb max pressure job. Engine is 63 259, v8 dual exhaust, carter AFB,, with half inch riser. Stock cam.

    I have been told to look for vacuum leaks, and adjust the idle mixture, which I have not yet done. Any other theories or places to look.
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  2. Magnum Wheel Man
    Joined: May 11, 2011
    Posts: 424

    Magnum Wheel Man

    is it possible your distributor is getting worn, & when it starts getting warm, loosens up a little allowing for non precise timing ???
  3. Did this problem just start, is it a new problem?
  4. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    from central NY

    This motor has not run more than 20 minutes in my possesion. I am in the finishing stages of putting this project on the road. So I can not say how it behaved before.

  5. bobwop
    Joined: Jan 13, 2008
    Posts: 6,098


    is your coil starting to give up? or perhaps a bad connection from the coil?

    also, check ignition switch for loose connection
  6. OK, could be lots of stuff. Hears how I would approach it, without any history.
    Re do the compression test on the engine after its warmed up. Be careful not to burn your self.
    Be sure that the ignition system general tune up parts are quality new pieces.
    Check to see that the advance mechanism is working properly, not sticking, and vacuum pot is OK.
    Check your fuel pressure, 4-5 Max on a carter.

    After you are 100% certain the above is good, then you can narrow it down if the problem is still there.
  7. EZ Cool
    Joined: Nov 17, 2011
    Posts: 261

    EZ Cool
    Alliance Vendor

    Clean and file or replace the points and condensor. Make sure all electrical conections are tight and not corroded especially the ones on the coil. Check coil wire itself for corrosion. Check all grounds, make sure the distributor itself is grounding good. Leaving it loose can cause a problem. All this is from experience. had it all happen and cause the same problem.
  8. Also check valves.
  9. Yup...your exhaust valves are set too tight. As the engine heats up, the lash goes away and the exhaust valve can no longer close all the way, causing the exhaust gases to go into the exhaust system when the valve is supposed to be closed..
    Reset exhaust valves to specs and recheck intakes while you're at it.
  10. sqhd
    Joined: Sep 9, 2006
    Posts: 71


    Yup times 2
  11. c-10 simplex
    Joined: Aug 24, 2009
    Posts: 1,346

    c-10 simplex

    What does backfiring only on deceleration mean?
  12. Mrmowerguy
    Joined: Jul 1, 2012
    Posts: 16


    Too much advance. I bought a car 500 miles from home, drove it through the mountains of Maryland and going down the hills it sputtered and backfired. When I got home and did a tune-up I found there was way too much advance on the distributer. It was like 20 degrees at an idle or something high. I replaced the points, condensor, plugs and wires and set it on 8 degrees and it never backfired or sputtered on a deceleration again.

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