One of my many dissertations.......
In retrospect, I've melted a few engines in my time. well not melted them in the liquid sense but melted holes in the pistons from running a little too lean. 2 stroke engines, especially ultra high performance ones are extremely sensitive to melt down so it's advantageous to always keep many heat ranges of spark plugs on hand to tailor the plug to particular conditions. You want a plug to run a tan color with no blistering on the insulator but you don't want a plug to be running dark brown or black. The easiest way to do a plug check is to perform what's called a plug chop. You bring the engine to operating temperature and then do a WOT run and immediately at the end, chop the throttle, pull in the clutch and hit the kill switch. Coast to a stop and pull the plug(s). The read the plug for color. I always ran Bosch Fine Wire Racing Plugs in my sleds as they resist cold fouling and have a good life expectancy. I always stayed away from Split Fire plugs because they tend to flatten the flame kernel (that's what the spark is called) and flame kernel shape is critical in a 2 stroke. When I holed my T'cat (I discussed that in the thread on timing sprockets), the engine was under warranty and I didn't actually melt it due to a lean condition but rather a faulty oil injection metering pump and that caused a big end rod bearing to weld to the crank, break the rod and blow it through the bottom of the crankcase.
I suspect this winter, like most winters, I'll be doing a bit of cylinder re-boring and sleeving as well as piston matching in the shop. Sledders always run their engines at the fine line between reliability and maximum horsepower per cubic inch and it's easy to cross into that grey area of a too lean condition and meltdown.
The more power you extract from any engine of a given displacement n o matter what type of aspiration it is, the more critical heat range of spark plugs become. It's a nice engineering scheme to have underside crown oilers on an engine as that pulls the searing heat of combustion away from the piston crown and takes any localized heating (as in incorrect heat range plugs) and dissipates that heat over a wider area but the heat range is still critical though not as critical as a 2 stroke high performance motor.
