ORIGINAL: av8tor1977
I haven't been following this closely, but a comment anyway. On some chain saws I have had apart that don't have a large phenolic carb insulating spacer, they have a small spacer such as you are using. But, this is important, they have insulating sleeves ON THE BOLTS that mount the carb, and fiber washers under the nuts that hold the carb on. This prevents the heat from transferring through the bolts into the carb...
AV8TOR
I like the idea of the insulating washer under the head of the screw, because in that case there is metal-to-metal contact. A great heat conductor. But for the screws, I still maintain just air is a better insulator than any sleeve put in there. My guess is the sleeve is for centering, not insulation.