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Engine Stuttering/misfiring at high revs - 289

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    Engine Stuttering/misfiring at high revs - 289

    Hello,

    I have a 1966 289 V8.

    I have been restoring over the past 2 years, when I first started restoration engine fired up fine and ran smoothly. I am nearing completion of restoration now, and started looking at the engine again (it hadn't been started for 6 months+).

    I started the engine a few days ago, runs very smoothly at idle or low RPM, however when at high rev it sounds like it is misfiring/stuttering. I have changed all the spark plugs, and the problem still persists.

    Any ideas of what would be causing the problem?

    Thanks.

    #2
    Fuel mate , Take the carb of and clean & blow it out with a air line . Modern fuel leaves a lot of sediment when the fuel evaporates . Dont go buying parts yet , start with the simple stuff & work from there .

    69 Convertible ,05 GT , 53 F100 , 59 Impala .

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      #3
      Thanks, I will give the carb a clean. It probably did have a fair bit of old fuel still at the bottom of the tank/lines.

      Comment


        #4
        Worth checking plug leads but fuel would be my guess.
        Gazza

        "Understeer is when you hit the wall with the front of the car, oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall and torque is how far you take the wall with you"

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          #5
          How old is your ignition coil, they can go bad at high revs.

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            #6
            Fairly old, came with the car. I am going to clean carb and try to flash the old fuel out.

            If that doesn't fix it I will replace the coil.

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              #7
              My first thought was coil for sure but the answers above are all excellent.

              I would change the coil regardless

              Good luck, Peter
              Please visit our Classic Mustang for sale site: www.classicamericancarsales.co.uk
              We stock a large selection of freshly imported Classic 1960s Mustangs. Fastbacks, Convertibles and Coupes. Cars are in stock in the Southeast of England with more shipping from the USA at all times. Other interesting American cars also stocked. CSRP disk brake setups sold

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                #8
                A high RPM misfire says more to an ignition problem than it ever would fuel.

                There are lots of things that can lead to this from coil voltage breakdown, to points bounce (if you are still on points), to no points gap to a HT lead issue, to a condenser issue, to a spark plug issue.

                First up I'd check a spark on each plug using a tester light.
                Second up I'd check the points have a gap.
                Third up I'd check the points gap.
                Fourth up I'd check the condenser.
                Fifth up I'd check the timing advance at high revs (to check the distributor weights are centrifugally active)
                Sixth up I'd check the engine timing.
                Seventh up I'd check the coil resistance
                Eighth up, put the kettle on and think fuel pump or filter or carburation.

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                  #9
                  Check your exhaust gaskets on cylinder number 5 :-)
                  Classic pre 75 Ford and Chevy addict who Works in Software industry & also part owner of a small LTD Shop that imports Cool / custom pre 1970 American Cars / Trucks https://www.horsepwrkustoms.com

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                    #10
                    Not really something that is easily diagnosed on the internet.

                    Hope it doesn't still have points..................

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                      #11
                      Originally posted by yanktankmad View Post
                      Check your exhaust gaskets on cylinder number 5 :-)
                      Why cylinder No. 5 specifically?
                      sigpic

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                        #12
                        If you think it is one particular cylinder, change everything on that cylinder to the opposing cylinder and see if it changes cylinders. A - no cost, B - you have narrowed it down to what it may be. You can then change the lead back and see if it swaps back, if so, the lead is at fault, if not itís the spark plug. Cost 1 hours messing around, and hopefully 1 spark plug

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                          #13
                          I had an issue like this on an old Land Rover. You could let it tick over for ages without a problem but take it for a run and once warm it would stutter and stall, you could restart after a short period of time. It turned out to be the coil so a nice cheap fix, let us know how you get on.

                          1966 Coupe: 1995-
                          1966 Land Rover Series 2a: 2012-
                          2005 Mustang GT 2014-
                          2007 California Special Replica: 2010-2014

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                            #14
                            Still got a few issues.

                            Cleaned Carb
                            Replaced Coil

                            Improved idle, revs but when you hold at high RPM it stutters/misfires still.

                            Any suggestions?

                            Comment


                              #15
                              Vacuum advance? Could it be advancing timing too much (or not enough) causing the engine to run rough/funky.
                              sigpic

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