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backfiring out both ends

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  • backfiring out both ends

    '47 Champion...backfiring out both ends.....What is the problem ?? I have installed new points and a condenser. Cleaned the cap, rotor, plugs. I have fire to each plug. I have the distributor set according to the "ign" and pointer on the engine. It backfires infrequently in the carb and once in a while out the exhaust. The engine will not run. The engine has been setting for a long time without running...........Brad

  • #2
    Could be you have some valves stuck. Have you tried a compression check?

    Dick Steinkamp
    Bellingham, WA


    • #3
      Backfiring occurs when something is out of time in relation to the spark getting to the cylinder at the correct time. Maybe a wiring error or wires going to the plugs, or something along those lines.
      Double check the spark plug wires using the service manual to insure you don't have one crossed, or two or more crossed. I think the rotor turns counter clockwise and you can check that the firing order from each spark plug wire is going to its correct cylinder when you find out the firing order.

      Don Dodson


      • #4
        Backfiring out of both ends...sounds like the results of eating a bad taco. I guess it's best to first understand why a backfire occurs. In the carb, it's because of the fuel-air mixture being ignited before it gets into and is trapped inside of the cylinder. As Dick said, an intake valve sticking open, at least partially or intermitently, could be the cause because when the plug fires, there's nothing to keep the fire from traveling back up into the carb. It can also be caused by excessivly advanced ignition timing that has the plug firing before the intake valve gets a chance to close. On engines with a chain driven camshaft, sometimes a worn out, loose cam chain can jump a tooth and alter the valve timing causing the intake valve to still be open quite a bit when the plug fires. That shouldn't be a problem with a Stude and the cam gear, if it jumps time you have a really worn gear.

        Backfiring out the tail pipe when trying to start an engine is usually caused by raw gas that has made its way into the exhaust. This could be from excessive cranking or pumping the gas when trying to get a recalcitrant engine started. It could also be from the carb float valve sticking open or leaking and allowing gas to run through. When the engine's running and you let up on the gas withit still in gear and it backfires out the exhaust, that's usually from running too lean of a mixture. Lean mixtures burn slow and unburned air-fuel charge gets sucked into the exhaust where it's ignited by the next exhaust pulse.

        If your engine isn't running, the exhaust backfires are probably from raw fuel running through. As Dick suggested, you might check the compression first. If everything seems ok, or at least all cylinder readings are even, make a mark on the distributor so you can return it to the current position. Then try retarding the ignition timing a bit and see if it will start and if the backfiring stops or at least is reduced. An engine will run with the timing retarded considerabaly, not very well, but it will run. If that doesn't do anything, try advancing the ignition. If it's too far advanced, a good clue when trying to start is the engine will hesitate or stop turning over when cranking it over with the starter. This is because the ignition fires while the piston is still coming up and as a result, the combustion pressure overcomes the starter torque. As far as I'm concerned, on a well used engine the timing marks are a good place to start but not an absolute.

        Last but not least, a weak ingition will often cause backfires from either end and hard starting. Try sticking a spark plug in a wire and let the plug rest on the engine block. Crank it over and see it you get a fat, blue spark. If not, or you get a yellow or orange one, that could very well be the problem. A lot of carburator problems are cured by working on the ignition. A good healthy spark will ignite mixtures that are too rich or too lean, but with a weak spark, everything has to be perfect or it won't do anything.


        • #5
          I second checking that the plug wires are correct on the dist. for the firing order. Been there done that!!! Let us know what is was after you fix it. Good Luck

          1956 Studebaker Pelham Wagon Houston, Texas
          Remember, \"When all is said and done. More is always said then ever done.\"


          • #6
            Plug wires are correct...Brad


            • #7
              Did some one have the distributor out? It cloud be in 180degrees out?That would make it back fire out both ends.

              63 Twin Supercharged Avanti
              64 Avanti R3w/NOS
              88LSC Avanti 350 Supercharged w/NOS


              • #8
                I just got the car, but it doesn't look like the distributor has been out....Brad


                • #9
                  Take out no 1 plug, turn engine to TDC-mark on the pulley. Check that no 1 valves are not depressed. You are now at Top Dead Centre and the rotor should be almost at the no 1 plug lead position.


                  • #10
                    Compression check: 40..40..70..50..0..0....I have soaked it for three weeks with Marvel Mystery Oil. Tried to turn it over 3 times a day and the compression has not changed. What's next ???............Brad


                    • #11
                      Sounds like Nos 1-4 have stuck rings and Nos 5,6 have stuck valves. I'd suggest pulling the head to verify this. A new gasket won't cost much and won't hurt anything. If the 5 and 6 valves are sticking up, spray some Kano Kroil, or maybe ATF (AutoTransFluid)on the stems and let them soak a couple of days. Do the same for all pistons to aid in ring release. After the valves have soaked, tap them with a block of wood, or the handle of a hammer. They should drop down. If not, go for a rebuild. If they do, reinstall the head and try it out. Stuck rings will free themselves [eventually]if lubricated with 10 W 30 and STP.

                      Tom Bredehoft
                      '53 Commander Coupe
                      '60 Lark VI
                      '05 Legacy Ltd Wagon
                      All three Indiana built OD cars


                      • #12
                        Well, the only time I have trouble with backfiring out both ends is when there's too much onions in what I'm eating. You might want to try... What was that Pauline? Oh, a car. Um...[:I] Nevermind![)][:I]

                        Lotsa Larks!
                        K.I.S.S. Keep It Simple Studebaker!
                        Ron Smith
                        Where the heck is Lewiston, CA?
                        Home of the famous Mr. Ed!
                        K.I.S.S. Keep It Simple Studebaker!
                        Ron Smith
                        Where the heck is Fawn Lodge, CA?


                        • #13
                          quote:Originally posted by bradnree
                          I have soaked it for three weeks with Marvel Mystery Oil.
                          Soaked what? If just squirted into the cylinders through the spark plug holes, it might help free stuck rings, but will not help stuck valves. Tom's idea is what I would do at this point. Be careful taping those stuck don't want to break the valve guides.

                          (BTW Tom...I've got an Indiana built GMC Sierra. My Hawk was built in Hamilton, my Starliner in LA, but my M15 is an Indiana vehicle too )

                          Dick Steinkamp
                          Bellingham, WA


                          • #14
                            MMO into the spark plug holes. Sounds like I just need Tom's and Dick's beautiful coupes in my garage...............Brad


                            • #15
                              If the engine sat for a long time, you might want to check the condition of the valves and seats that are stuck. Setting open for a long time is a good way for the seats to get rusty and pitted and also the valves if they aren't stainless.