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Peletz, at the high input (from switch NOT to coil) coil terminal when the ignition is switched on you ought to see around 6 volts setting and maybe 4.5 or better while cranking (depends on battery n starter n cables etc etc). If shes (battery voltage) too low you get a weak spark. If voltage is low on the coils input, the first thing I suspect (if not a battery or starter or cable or connection problem) is a bad ignition switch with loose or carboned contacts. One way to check is to temporarily jump a hot wire direct to the coil and then measure voltages setting and running and if she has a strong spark then and runs better, I would check the switch and the wires from the switch to coil and also the voltage and wiring to the switches BAT input terminal to see if its around 6 as it should be setting. If the switch shows near 6 volts on its BAT input terminal but with the ignition on and points closed only shows 3 to 4 volts while setting on its output (to coil) terminal (NOT cranking) THE SWITCH IS BADDDDD DDDDD DDDDD DDDDD DDDDD it has resistive contacts and/or carbon. If the voltage on the coil setting with ignition on and points closed is near 6 volts but drops drastically to like 3 while cranking and the switch is good (or shes hot wired), then I suspect a weak battery or a bad starter or bad or too small or corroded cables or connections. I recommend 00 Gauge Battery n Starter n Ground cables on 6 volt applications. Another cause of extreme voltage drop while cranking is a poor ground connection, maybe try grounding to a soild frame bolt versus any thin or rusted sheet metal somewhere, the closer to starter the better. I would remove, clean n wire brush and reattach each n every battery n starter n ground cable connection then try it. To be safe, charge the battery and better yet have a shop load test it !!!!! !! and/or try a know good substitute battery to see if that helps. If the battery and cables n connections n grounds are all good but voltage still drops drastically to like 3 while cranking, I suspect a bad starter thats drawing excess current, it may have a shorted or dragging armature or bad brushes etc etc. Drastic battery voltage drops while cranking causes a very weak spark and hard starting. Besides the ignition switch, a bad/carboned starter switch or solenoid can cause poor cranking performance and voltage drops. Once the voltages are all up to par (6 on coil setting and 4.5 and over while cranking) and she has a good battery n cables n grounds but the sparks still weak, post back for my non or weak spark Troubleshooting Procedure. HOWEVER make sure the points are good (not burned or pitted or all carboned up) and gapped proper and you have good wires n plugs in the meantime as that affects spark quality big time. John T in Indiana
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