Well, the thing is how does one know whether the carb mounting bolts are touching the carb body somewhere or not? With the sleeve on the bolt, you know it can't touch metal to metal. Anyway, that's how it was done on at least one saw I had apart one time. I think it was an older McCulloch saw.

Shrink tubing would probably make a good bolt insulator/sleeve....

I think unless it is really a very hot installation, the only problem encountered with a non insulated carb setup would be vapor lock after having been run. Without cool fuel running through the carb, and cooling air, the fuel boils in the carb and can make hot restarts tough.

AV8TOR