91 octane to stop vapor lock?

I have a stock 198 Slant six (71 Scamp)
The same story, runs like a dream on the highway, but chokes in the city.

*I've since had an Electric Fuel Pump with return line put in and re-plumbed the fuel line which solved everything :cheers:.
Would filling up with 91+ octane (no ethanol) alone been enough to stop Vapor lock altogether?

Curious to see what you guys think.