low power when hot?

I will post some plug pics when I swap them.

is there something specific you would like to know about the engine that might help you? as far as I know its stock aside from the bore.

So of 87 is just OK, what should I be putting in it? Also - I'm slightly out in the country so there's not really a broad selection of gas
Well the size of the engine is a good place to start, /6, 318 or 340?
Factory stock carb, ignition, exhaust? Automatic or shifter car?