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Engine backfire through exhaust with all new parts installed !

Discussion in 'The Hokey Ass Message Board' started by Retro Jim, Aug 25, 2011.

  1. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    This is a first for me and I am scratching my head right now . I am good at figuring out the problems but I m not doing good with this one .
    I have a Ford 302 with a points distributor , coil , 2 bbl carb . It's on an engine stand . I have the distributor hooked up to an on/off switch with a push button for the starter . I have a one wire alt hooked straight up to the battery side of the solenoid . I have a resistor hooked up between the battery and the hot (+) side of the coil . that also is on a on/off switch .
    Engine has headers and mufflers . The engine came to me as a job NO RUNNING ! Had no carb , exhaust or alt . the balancer was off as well . No plug wire . He had a box full of parts and I picked out what I could use and bought the rest .
    This is what was replaced with NEW parts !
    distributor cap
    spark plugs
    one wire Alt
    all wiring is new
    new fuel pump

    I also had to take the top off the carb because the float got stuck and had the needle valve closed so I got no fuel to the carb .

    The engine will start up no problem and runs . I have set the points , carb and the distributor I had to set by ear since the timing marks don't line up due due to the wrong balancer being used . It's still a 28 oz balancer ! The engine has been apart before from the signs of different gaskets that are not stock and signs of silicon being used .

    The engine backfire through the exhaust ONLY and not all the time either ! Backfire through the driver side on the number 5-6-7-8 cylinders . The passengers side fire OK I think and gets hot on the headers and muffler like normal . NOW the drivers side exhaust is cool and the exhaust gasses are cool coming out the exhaust ! Doesn't matter where the distributor is set , it still back fires out the exhaust and not the carb . I used a stethoscope to listen to each header tube at the heads to see which exhaust valves the backfire is coming from . I hear the backfire in the number 6 & 7 cylinders .

    I am open to any all all comments or suggestions on this problem !

  2. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    from Kent, Ohio

    I would check for an exhaust leak, at head or wherever. If your engine is running rich, sometimes and exhaust can suck cold air (oxygen in) and when it mixes with a rich mixture it combusts, and sounds like a backfire.
  3. tucknroll
    Joined: Mar 10, 2007
    Posts: 104

    from iowa

    hello jim. just a thought but if that 302 is a HO version they use the same firing order as a 351 -- 13726548 ccw compare to the 302 with 15426378 ccw firing order. may want to check. good luck
  4. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    It's an early 302 . I did see another post about someone having the same problem and many said it's the headers sucking in cold air and causing it to backfire . The backfires sound like a shotgun going off !

    Retro Jim
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  5. George/Maine
    Joined: Jan 6, 2011
    Posts: 949


    I had a problem were it would idle only 14lbs vac,after changing timing chain,carb,dist.So my last shot was to put a new cam Elbrock good idle up 5000 rpm.When taking it apart i found a bent push rod.I do,nt think that was my problem,cam lobes were more round on old think it was hot cam.Can,t fight success it runs good now.
  6. Do the cheap and easy things first, look for signs of exhaust escaping at the header flange. Maybe throw some copper gaskets on it, those seal nicely.

    The only other thing I can some up is maybe you have a sticky valve from the motor sitting around. Pop off the valve cover on that side to see if the push rods and rockers look okay.

    If it was mine, and everything looks good, I'd run some Marvel in the oil for a while to see if the condition improves.

  7. Jim
    You already know that I mostly work on GM stuff sop what I am going to say will probably have little bearing on your problem. Never the less you will go well that makes sense comming from a GM type.

    once I wired a Ford that I had up backwards. I was scratching my head so I called the Ol' Man. He said, "What way does the distributer turn son?" There was a short silence then lots of very loud laughter from what sounded like dozens of people, I guess he had me on speaker phone. The car ran although a little sluggish and backfired on the drivers side.
  8. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    I have done a lot of GM engine too over the years working at dealerships . I was a GM mechanics first and when i bought my first Ford and did a cam swap I had a hell of a time trying to get that engine running . I did the same thing you did with number 1 cylinder . I think we all have done that one before too .
    The engine did run fine when I first got it running . It also had the stock manifolds on it too ! So since I installed headers and a one wire alt , then this back firing started up . I pulled that damn distributor 3 times to make sure I got it set on number one TDC ! I know the header leaks on the passenger side .so I will replace them and see what happens .
    The engine has plenty of get up and go but this back firing has me puzzled a lot . I never had this happen in over 40 years of building engines . I guess there is a first time for everything !
    I will let everyone know if the header gaskets was the problem or know !
    Thanks to all !

    Retro Jim
  9. 61 chevy
    Joined: Apr 11, 2007
    Posts: 891

    61 chevy

    maybe a broke valve spring, :eek:
  10. parklane
    Joined: Oct 17, 2009
    Posts: 188


    Jim, just put the manifolds back on and see if that stops the backfiring.
  11. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    Thanks for all the posts and help . I have done more tests to the engine and started a different post with all my test results . So please continue with the ideas for helping me figure out what is wrong with the engine !

    The new post is called " The engine that won't behave !"
    Please go to that post .
    Thanks to all for the help and suggestions !

    Retro Jim
  12. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    Well I removed the intake and the nightmare has begun .
    I did replace the intake gasket and as I was filling the radiator with water all the sudden the water started pouring out the intake gasket at the water jackets in the front . Now I know why the last person used a 1/2 tube of silicon on the gasket .
    So I drained the water and pulled the intake . I used a steel straight edge on the heads and they were true . I then use that same straight edge on the intake and OMG , it looked like a motor cross dirt track . The intake is full of waves ! Both side is like that . Well I will have to find a sbf 2 bbl intake cheap someplace . That was the whole problem from the start . The last person trimmed down the front and rear cork gaskets on the intake and used a 1/2 tube of silicon on both sides of the side gaskets hoping that would hold .
    Well the nightmare continues to go on and on !

    Retro Jim
  13. morac41
    Joined: Jul 23, 2011
    Posts: 532


    Hi Jim Could have a 351 cam installed ...they fit .....different timing...would explain backfire exhaust.....
  14. Retro Jim
    Joined: May 27, 2007
    Posts: 3,860

    Retro Jim

    The intake is badly warped ! Found out after I replaced the intake gasket with a new on then filled the radiator with water . Then all of a sudden the water started coming out the gasket in the front at the water jacket ! I pulled the intake back off and checked the head surface with a straight edge and the head surface is true . Did the same thing to the intake side , both were terribly warped and not true !
    Now I need to find a cheap or free sbf 2 bbbl intake !

    Retro Jim

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