If the carburetor jetting worked with the old head, it should work with the new head. I interpret fine tuning to mean synchronizing the throttle plates of the two carbs and setting the idle mixture screws. This needs to be done and should reduce or eliminate the spit-back but I am not confident these adjustments will impact your temperature issue.
I guess I assumed that new jets were put in the carbs without much regard for what was in them before.
I should've asked, but it's too late now.