The Stovebolt Site Forums The Shop Area The Electrical Bay Sparkplug cable resistance.

I'm running a pretty standard ignition system. Coil with ballast resistor. What should the resistance of the lead from the coil to the distributor be and what should the sparkplug cable resistance be? I'm having starting problems. Coil tested ok but the spark looked yellow instead of blue when checked. Cheers

That's not something to worry about. I would just buy a plug wire set. Copper conductor is best. Some folks perfer other types. Whatever you like. I used to say buy good quality, but that is now impossible to determine using brand names as a guide. I now try to buy from local or Amazon, where I can take back with no hassle.
I would put the cause of your trouble at plugs, points or CONDENSER/capacitor. New wires and "tune up" items mentioned is a good boiler plate start however.

If you need help with starting you will have to specifically explain "starting problems". Spark color is subjective. What "starting problems" means is objective.

1. Slow engine cranking speed
2. Starts and dies
3. Starts and runs good but takes a long time to start
4. Takes a long time to start and also runs bad
5. Does not actually start but pops, backfires, spits
6. Starts only when cold or only when hot
7. I notice when it xxxxxx, then it will xxxxxx
8. Please specify year make model of vehicle and motor and 6V or 12V.
9. Yellow spark will explode gas.

Radio frequency noise suppression ignition "wire" has been in use since the early 1960's. It's not wire at all, but a piece of string infused with graphite and other conductive material. It can have a resistance of up to 1,000 ohms per inch. It's there to suppress the magnetic signal generated by current passing through the ignition leads that causes interference with radio and TV signals. A yellow spark is normal. The "hot blue spark" that people still look for is as obsolete as a hand crank for starting an engine, or a carbide generator to power acetylene headlights. Using wire-core ignition leads will cause rapid erosion of the contacts inside a distributor cap due to the high current involved, however.
Jerry

Vehicle is a 1957 3100 with a 283 small block. 12v system. It takes ages to start and will sometimes pop and spit. When it does start it runs OK .

Put it this way large aircraft engines don't use resistance wires, nor do lawn mowers or chainsaws. The higher the resistance the more power the coil has to put out and that means heat. You know similar to connecting a 1500 watt
space heater to your little 2000 watt portable generator, what causes it to work harder the 1500 watt higher resistance or a 100 watt lower resistance light bulb?
Almost no one uses AM radio or non cable tv, to have to worry about RFI any more.
Some have recomended 500 ohms per foot that I have seen. A solid wire will have almost zero ohms per foot.
Also for starting problems make sure the resistor bypass is working.

Squirt gas down carb when cranking to see if you get an immediate start....or any indication of improvement. Report.

For many years I always made my own plug wires using copper wire with soldered on ends. I never had a problem. But today, I've finally given in, and am using factory made modern wire sets. Much easier to find and save lots of time. I cannot tell a difference in starting. If I were looking for a weak spark problem, I"d start on the low voltage side, i.e. every connection from the battery clear up to the points. A dirty, oily, or poor connection at the ignition switch, ballast resistor, coil, or distributor can cause weak spark. Poor starting can have many other causes too though. For me personally, intake leaks have been the most hard to find and to isolate, although more on small engines than on stovebolts. Some modern coils don't need a ballast resistor to be used with them. If you have one of those, and are also using an external ballast, that could cause low spark voltage.