Hi Gary, you may know a lot of this , but here goes ! Many do not understand these dual points .. Including me , way back . Can drive you crazy. Check for damaged "flex"wiring inside distributor , ( it can break intermittantly under / inside the rubber -- pull on it ! -- and check with low range ohmmeter) . But most likely just not adjusted right . Did you use dwellmeter ? 2nd set closes right after first opens at the spark instant . Unbelieveably critical to get it perfect/ right -- especially down in the hole in back under heater . @@$$"""as you say . I cannot do it in car anymore . . If 2nd set closes too soon , it misfires . Or same thing , first spark set opens , but the second still semi closed . And everything in between . Once set up right , really good , quite stable . I think just as good as any pertronics , and it wont just die suddenly . Probably ok for 20-30 k miles at least . Sometimes process of tightening clamp set screw down causes it to change after setting up carefully . ( Dwell meter will still show anything wrong, after you are all done) --cheap on ebay , as cannot use w electronic ignitions . Due to many tolerances wear etc , i would only trust dwell meter , ---that also ensures hot spark at higher rpm.. With right dwell. If not right dwell , ( too much or too little overlap) it will also break down at hi rpm even if runs ok at low / med rpm . The whole reason for two sets is to up dwell time to charge coil up fully for hi rpm , between successive sparks . That longer current on time (dwell) gives the coil more time to store up spark energy in the coil magnetic field for full power for next up coming spark . ( EE hat on) So they close circuit again as fast as they can after a spark ( 2nd set closes , they do not wait a lot longer for a single set to go ever the hump and then close again ( like GM!) . Note that both sets open and close per each spark , 8 lobes . Not 4 cyl per points set ( some Mallory did that , 4 lobes ) . Great design really but matchbook cover setting wont cut it. If mechanically perfect setup , ( gap) it should work but dwell meter tells you it is working . A Coil failure cannot ( generally ) do what you are seeing . It dies , might come and go , but dies . A Bad capacitor can reduce spark , cause hard start and very poor running . . A lot of the new capacitors with stamped lines or crunched marks on the plain end of can are flat out junk . They crunch in that end to make crude "touches only " contact with inner wound aluminum foil, it gets intermittant .I took one apart and found all burn and electrical corrosion marks where it had been arcing in there . That --after chasing intermittant ignition performance hassles for several years . ( capacitor is brand new --it cannot be bad !-- changed everything else a few times!! ) Find your old one , test with ohm meter put back in! Spark should be hot and strong .. Jump like 3/8 + in air .
To test capacitor , put analog ohmmeter on high ohms ( megohms ) touch the leads to cap can and wire . Needle should swing up a ways and go back to infinite ohms, or 10 megohms + . Reverse leads --it will do it again . ( reverses the stored charge on cap) Cannot do with a digital meter . But an intermittant inside can confound you . No swing = open cap . Swing that stays up =, shorted or leaking cap.
It went 140 mph with no electonics, right ?
Don't join the "i dropped the tiny screw club". I am a member since 1961 . When i tuned up a perfectly running 392 hemi , and could not get it to run at all after . At 18, that is the end of the world. A few times over . The screw then falls under the points plate . Auuugh . Many hours later ---/Get an electrician's small size screw holding screwdriver . Hard to find a short one , the kind that reaches solidly around screw head .. And follow service manual to a T . Before you start be sure points are square and aligned concentrically . You do not want edge only or tilted / off center contact . Cant gap that . Sometimes they need a tweak first . Good luck !
John Grady
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To All, Have replaced Pertronix with factory dual points. Car ran great with factory set up. Went to start and backfired and felt like it was only firing on 4??
Re-Replaced the condenser and all was good (I thought). Drove about 10 miles and put away. Went to start next day and back to backfiring and 4 cylinder's!!
Figure I will replace coil. Any other thoughts.
As Always, All suggestions Greatly Appreciated.
gary gettleman