I have a question concerning the multi core abilities of the JForex platform. I figured that the historical tester sometimes runs on both of my cpu cores, while sometimes it only uses one. How can I influence the number of cores used for testing? What is the maximum number of cores? Increasing the process priority didn't help.

Thanks

The way how program uses your cores depends on operating system. It's a duty of OS to provide one of the cores to the every thread in program. If it always gives one core you will see one core fully loaded and all other free. Usually threads are reassigned every few milliseconds to different cores randomly (or it appears so) and you see that all cores are loaded equally but only for 50% or less (if you have 2 cores - 50% if 4 then 25%)
Strategy tester logic is very sequential because all ticks should be processed one by one in the same order they was created (ordered by it's time). It's not easy to make it work in parallel in more than one thread.