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  • miss at 2200 rpm...

    i seem to have a miss, or maybe better said, a little bucking at 2200 to 2400 rpm at a steady speed.

    after getting the car back together (replacing head gasket, new cam, etc) i started the car to break in the cam and lifters. i ran the car for 20 minutes at 2000 rpm. during that time i had some popping and missing. not a regular thing but it would pop and miss even down to idle. after the run i went in and set the timing with a light. no more miss. thought i was good.

    then i had the freeze plug leak and had to go back in and fix that. started the car again and all seems fine. so i put the hood on and took a test ride. on that ride and everyone since, i have this slight miss or little bit of bucking at 2200 to 2400 rpm. can't even say it is consistent.

    above that RPM it seems to run fine. it idles fine. (maybe a little lope at idle but not much) it accelerates fine. no miss under load at high or low rpm. hit the gas and it goes. even if i am running 2200 rpm and hit the gas. no hesitation.

    no back firing thru the carbs or exhaust. So that made me think, maybe a fuel issue? but i have no hesitation under acceleration. Low rpm or high. and above 2500 rpm at steady speed no issue.

    spark plugs? i broke a plug taking them out so bought new ones. i did go from champion RN12YC to NGK, BP6ES. wrong plugs?

    i replaced the fuel filter during the build.

    i have played with different timing settings.

    since i had the head shaved, i put new gas in today and went to 93 octane. although there has been no pinging or knocking.

    i am running Pertronix but i have run that since i had the car with no issues. i actually have a spare setup and i tried the black magnetic cap out of the new box but no change.

    i know i am close and it is something simple. car runs too well the rest of the time to be anything real bad.

    suggestions?

    Thanks

  • #2
    I went from Pertronics and NGK to points and Champions.

    I suggest trying the Champions again at a reasonable gap for a quick easy test
    '74 TR6 CF13007U aka "Mr. T"
    Custom Blue (Delft-Like) and New Tan (Formerly Mallard and New Tan)
    Points, Ballast Bypassed, Bosch Blue Coil, Moss Cobalt Wires, Champion RN12YC plugs.
    Peaks and tweaks, but the spirit of Original
    Redlines always.
    My wife is the Driver, I'm just the Mechanic....

    Comment


    • #3
      And, check the condition of your low-tension lead wire (the one from points post to side of dist. cap).
      They tend to disintegrate inside the sheathing, and cause a miss & eventually a no start.
      Walt
      CC80954U '72 TR6 original condition/sold 16.500.
      poolboy rebuilt the Z-S Carbs. Philstr6 rebuilt both rear hubs.
      Wisdom comes from experience, experience comes from lack of wisdom.

      Comment


      • #4
        I second Harris' idea. Night and day difference in my car. I had a petronix also. Good luck and let us know how it turns out.
        1972 Sapphire TR6 #CC84,something

        1959 Red TR3 (Wife's)

        Comment


        • #5
          For some reason i had in my mind that the BP6ES was a cross-reference to the RN12YC plug. after doing some reading last night it turns out that the BP4ES is the cross reference, which means i have running a plug two steps colder. that plus i may be running a bit rich, is probably just loading up the plugs at that range of RPM. Also it is colder outside and i am now running the engine with 4*advance on the valve timing, a spark advance instead of a spark retard... all probably leads to the engine running cooler anyway. these plugs probably just never clean themselves up.

          i am going to go back and try the hotter plug first, resisting the urge to change too many things at one time.

          Comment


          • #6
            So i went out and bought new RN12YC spark plugs. put them in and took a ride. the miss was worse and it was happening on low rpm accel.

            as i was pulling the BP6ES plugs out i noticed that the number 1 plug looked much worse than the others. in fact the others did not look real bad. it got me to thinking that maybe i was having an issue with the spark to that plug. first thought was i broke a plug wire. started digging around in boxes (because i rarely throw anything away) and found the old set of plug wires. so i replaced all the plug wires. i felt the car ran better but still felt like there was a bit of bucking at around 2000 rpm now. and still the low rpm accel seemed off. that discovery made me want to eat lunch. So i did. after lunch i went back out and ran an ohm meter of each plug wire. nothing seemed out of place. So i pulled all the old wires off and then pulled the cap. i started looking for a crack or something i may have missed. did not see anything.

            then i pulled the rotor button to see if maybe i filed one of the contacts too much.... and then i saw it. the new rotor button was a good gap from the contacts when centered. So i went back to the drawer (remember i never throw anything away) and grabbed my old button. Click image for larger version

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            This is one of those things where i got the diz back rebuilt and never really checked. i pulled the points out and put in the pertronix. put the new rotor back on and that was that. guessing Bob just pulled the wrong one when he did the rebuild. he also did my Healey which is a 26D, i think, and he had the right rotor on it.

            it is surprising to me it ran as well as it did. i guess the pertronix unit puts out a pretty good spark to jump that gap. it also explains why the car would start missing when i was advancing the timing. guessing the gap just got too big at some point.

            i did not really get to do much of a test drive after this discovery. it was starting to rain. but the little one i did felt smoother. i think this is probably the answer. when the weather gets better and i can get back out, i will test on a longer run. then i am going to play with the timing again and see if something feels better.

            all's well that ends well.

            thanks for the suggestions

            Comment


            • #7
              Good deal. Saw that swapped rotor issue once before. Car ran, but did miss. Advanced Distributors web site used to be a tad confusing, if you didnt read close on the applicable dizzy.

              By the way, I think the NGK BPR5 are a closer range to the Champ 12Y...
              Last edited by tr6harris; 01-30-2019, 11:07 PM. Reason: Edit - Correct BPR7 to BPR5
              '74 TR6 CF13007U aka "Mr. T"
              Custom Blue (Delft-Like) and New Tan (Formerly Mallard and New Tan)
              Points, Ballast Bypassed, Bosch Blue Coil, Moss Cobalt Wires, Champion RN12YC plugs.
              Peaks and tweaks, but the spirit of Original
              Redlines always.
              My wife is the Driver, I'm just the Mechanic....

              Comment


              • #8
                on the NGK, the higher the number the colder the plug. opposite of Champion. all the charts show the 5 or 4 as a cross to the RN12YC.

                actually i may have gotten away with the 6 plug if not for the rotor. i am going to leave the Champions in for now and just see how they look after some miles. i have read from other posts where some people thought the NGK's cleaned themselves better than the Champions. i know when i was using the Champions before after a few hundred miles i would start to get some hesitation at lower rpm on accel. clean the plugs and it would go away for another few hundred miles or so.

                of course i had some other issues going on so may not be an issue now.

                Comment


                • #9
                  Was reading on another site how too rich fuel mix or too advanced timing could cause low speed hesitation, and consequently plug fouling. Something to keep in mind.
                  Walt
                  CC80954U '72 TR6 original condition/sold 16.500.
                  poolboy rebuilt the Z-S Carbs. Philstr6 rebuilt both rear hubs.
                  Wisdom comes from experience, experience comes from lack of wisdom.

                  Comment


                  • #10
                    yup, going to keep an eye on it. Thanks. it will be a lot easier to tell now that i should have a more consistent spark.

                    since this is a new setup with all the changes, i have started with the carb mixture set in the middle and the advance where it was recommended with the rebuilt diz. just need to get some miles on it and some longer runs to see how the plugs look.

                    Comment


                    • #11
                      Originally posted by Drone Dog View Post
                      on the NGK, the higher the number the colder the plug. opposite of Champion. all the charts show the 5 or 4 as a cross to the RN12YC.

                      actually i may have gotten away with the 6 plug if not for the rotor. i am going to leave the Champions in for now and just see how they look after some miles. i have read from other posts where some people thought the NGK's cleaned themselves better than the Champions. i know when i was using the Champions before after a few hundred miles i would start to get some hesitation at lower rpm on accel. clean the plugs and it would go away for another few hundred miles or so.

                      of course i had some other issues going on so may not be an issue now.
                      You are correct - BPR5. Getting old, cant rely on memory anymore! All I had to do was walk out to my bench to the ones I never installed... (edited my initial post)

                      That said, I love NGK, but the TR6 just ran better on the Champion RN12YC, so I am dialed in.
                      '74 TR6 CF13007U aka "Mr. T"
                      Custom Blue (Delft-Like) and New Tan (Formerly Mallard and New Tan)
                      Points, Ballast Bypassed, Bosch Blue Coil, Moss Cobalt Wires, Champion RN12YC plugs.
                      Peaks and tweaks, but the spirit of Original
                      Redlines always.
                      My wife is the Driver, I'm just the Mechanic....

                      Comment


                      • #12
                        I had exactly the same symptoms last summer - great acceleration below and above somewhere around 2500-3000 rpms, but the car stammered in between. I tried everything I could related to ignition. I inherited the car with petronix, so I replaced it. No change. Switched to points. No change. New rotor, cap, plugs, wires and ultimately a new distributor, timed perfectly, and still zero improvement. Because I had 1 year-old SU carbs (triple) I didn't think they were the culprits, so I then switched out the fuel pump and fuel filter thinking low fuel pressure at peak demand, or filter debris. Nothing. Finally, and out of desperation, I pulled the carbs off, did a light disassembly and cleaned them - including removing and cleaning the float valves - with compressed air and carb cleaner, then reassembled. Instatntly, problem solved. I was pissed off, then amazed, then relieved. Eight months later, it is running like a top. Not sure that's your problem, but it sure was mine... good luck.
                        Joe Murawski

                        '74 w/bits of '72
                        ... a perpetual work-in-progress...

                        Comment


                        • #13
                          Two of my miss episodes: 1 solved by new plug wires, 1 solved by carb service. Back in the day the rubber diaphragms in the carbs were good for years or 50,000 miles. With alcohol in all the gas and maybe today's inferior parts the rubber bits perish quickly, always chasing vacuum leaks.

                          Comment


                          • #14
                            The problem with this kind of hesitation is that like with personal health issues, the symptoms can come from many sources. I replaced plugs, wires, fuel pump, and each time there was a slight but only temporary improvement. Placebo effect maybe?

                            Then I sent the carbs to Ken. Car ran much better after his work, but there was still a definite - shall we say - "lack of interest" in the engine's willingness to accelerate through the 1500 to 2000 RPM band smoothly. Finally, on Ken's recommendation, I got a rebuilt dizzy from British Vacuum, with no spark retard and a spark advance. Problem solved.

                            I suspect that had I done the dizzy first, the improvement would have been noticeable but still not complete. All the intervening fixes were part of the overall problem. Everything has to be optimized to get the best from these engines.
                            1976 TR-6 BRG - CF57239U
                            Carbs by Poolboy
                            Rear Camber Kit, Rear Hubs by Goodparts
                            Gear Reduction Starter by TSI
                            Distributor by British Vacuum

                            Comment


                            • 70Damson
                              70Damson commented
                              Editing a comment
                              Bartman, What is a "dizzy?" Thanks.

                          • #15
                            Originally posted by familysimon View Post
                            Two of my miss episodes: 1 solved by new plug wires, 1 solved by carb service. Back in the day the rubber diaphragms in the carbs were good for years or 50,000 miles. With alcohol in all the gas and maybe today's inferior parts the rubber bits perish quickly, always chasing vacuum leaks.
                            Aside from the air valve diaphragms, I think the 'perishable' parts useful lifespan is about 7 years.
                            Diaphragms are worth checking annually... Normally there's no contact with the gasoline but high manifold vacuum such as in engine braking and high rpm downshifting will stretch them thin.... and if you have a backfires thru the carbs for whatever reason check them..
                            And thanks, Bart !
                            Driving a 1973 TR6
                            Doing ZS carb repairs
                            email kencorsaw"at"aol.com

                            Comment

                            miss at 2200 rpm...

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