Not going to argue about using the avgas in your engine, rather just stating a fact:
Use of the "octane selector" has already been mentioned.
Stromberg (one of the better carburetor manufacturers) stated that when using street premium fuel in low compression engines, the carburetor needed recalibration. Street premium is nowhere close to avgas in octane.
With 60 plus years experience of working on carburetors, I have found listening to the engineers often solves issues.
The only engines I have found where really high octane fuel works close to as well as the correct fuel are engines that have been HIGHLY MODIFIED. (Race gas works very well in my 350 / 450 with 10.38:1 compression, and 20 degrees BTDC timing.
EDIT: In the "for what its worth" category:
In 1950 "regular" gas would have been an octane of about 80 (RON) which is roughly equivilent to 77 (AKI); premium was approximately 85 (RON) which is about 82 (AKI). Stromberg stated the carburetor needed recalibration for premium (then AKI of 82). Avgas has an average AKI of 108.
Jon.
