Originally Posted by busman1965

I have been working on my recently acquired 1973 280 sedan. The original (and only) owner before me did conversion on the distributor to a Crane/Allison XR-700 Electronic Ignition (basically a points eliminator).

I noticed today that the car has Resistor type Champion RN9YC spark plugs as well as copper/silicone ignition wires with 5K resistor metal boots on them. This seems to add up to over 10K resistance between the coil and the plug gap, which seems like a lot to me. I recall these engines used to use 1K resistor wires and non-resistor plugs originally.

The whole reason I went digging into the ignition system was I noticed the original owner listed fairly frequent replacement of spark plugs in his maintenance logs (he kept insanely detailed records of every single item that was changed on what date and the mileage, as well as what symptoms if any required the change). It appears he has used the Champion RN9YC for many years, and it appears he also had swapped out the original 1K ohm wires for the 5K wires many years after installing the XR-700 Electronics Ignition.

The last bit of info is that the coil is a stock internal ballast resistor Bosch coil. Currently the car starts easily cold or hot and runs really well with no hesitation or flat spots, and still has the original Solex 4A1 carb. Its actually one of the best running carb'ed M110's I have ever driven.

I guess my question is do I need to look at getting rid of the resistor plugs and/or going back to the 1k plug wires? My concern is that the set up is causing the plugs to fail prematurely based on the frequency of plug changes noted by the original owner, who sadly cannot remember much anymore. Any thoughts or ideas on this setup?