I have the small plug head in my 80 aspen 1bbl. I was using Bosch platinum plugs, but just switched back to the OEM Champion RBL16Y. The Bosch showed lean with a #63 jet, so I jetted up to a #64 and the plugs looked good. After running the 16Ys, the plugs show lean again. Here's the thing, the Bosch were colder plugs than the 16Ys. Looking at the center electrode on the 16s, I can see the annealing ring is about midway between the tip and the porcelin, so the heat range should be just about right. The Bosch does not have a visible center electrode, so you cannot check the heat range in this way. So what do I do know? Jet up again?

Have any of you encountered this situation when running different plugs?

Mitch

Sounds like that #16 Champion plug is hotter then the Bosch.
If all the plugs are pretty even in color, I would just leave it alone.
Without a timeclock it is hard to fell "seat of pants" if the car engine is making more power if you go richer.
In general, the most power comes when they are a bit on the lean side.
DD

After the plug change, I had to retard my vacuum advance two turns (which is significant) because the engine started pinging. After going one jet size larger, I was able to restore my timing. All of this is at part throttle, so it is very subjective. I am not at WOT where I am time acceleration runs, for example. I'll examine the plugs again. If my fuel mileage does not suffer by much, I'll leave everything where it is.

Mitch