Carrier: No Sparks.
Hi Stewart,
I see that you already have several well informed replies re. your problem but I'll shove in my five pennyworth anyway!
As far as I'm aware, all the 6v flatheads,early or late, use a nominally 4v coil with a wirewound resistor between it and the ignition switch. This resistor is made from Eueka wire which has the property of increasing its resistance as it heats up. This has a very useful effect in basic ignition systems, i.e, the primary current is shared between it and the coil. When the engine is idling the contacts are closed for a relatively long time, so the primary current tends to increase giving the coil a hard time.
However, the resistor counters this so the coil does not cook.
On the other hand, when the engine is at high revs the resistor cools, allowing plenty of current to convert into high speed sparks.
Another handy effect of this system is that if the ignition switch is left on with the engine stalled, the resistor stops the coil going into meltdown if the contacts are closed. I think the resistor should measure about 0.75 Ohms at 20c.
Great care must be taken when setting the contact breakers on 8 lobe cams, as one set 'makes', and the other set 'breaks'. The contacts are NOT 180 deg. apart, which cleverly increases the coil saturation ( Dwell ) time to 36 deg., giving a better spark.A proper setting fixture is best but I have had good results using a vice to hold the distributor, wiring in a coil, plug, battery and resistor, using a drill to turn the dist. shaft at approx. 2000 RPM, using a dwell meter or 'scope to check the results.
A later development of the Ballast Resistor is the cold start bypass system i.e, when the engine is cranked over the heavy starter current drops the battery voltage from, say, 6v to 5v. A separate wire from a terminal on the starter solenoid is fixed to the coil primary terminal, bypassing the resistor, so now there is 5v to a 4v coil and, hey presto, big fat sparks to fire the old girl up! Clever huh! This system overcomes a problem known as coil robbing which some folks may have experienced by the engine firing just as you let go of the starter switch.
Sorry if all this comes over as a lecture but i've always found that things are much easier to fix if you know how they work in the first place!
Good luck,
Rhett Fisher
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