It is not at all uncommon to find best power short of full throttle.

 

A number of factors may be involved. There may be an imperfection in the manifolding that can be masked by turbulence generated by the throttle plates.

 

Poorly radiused runners may be assisted in turning the flow by a less than vertical plate.

 

Poor atomization may be improved by high velocity flow around the plate when angled, and then return when the plate is vertical. (going from rich to lean)

 

Dyno with the carb or throttle body facing both ways, so as to get all of the free power.

 

On my Fiat engines full throttle was 4 HP less than about 95%.

 

Lynn E. Hanover