problem tuning carb

catsncudas and I have been trying to get the "new" motor tuned in and the carb is acting funky so I thought I'd ask for some insight. The motor at idle is pulling between 5-6 pounds of vacuum and it has a 2.5 power valve installed. Ocassionally for no apparent reason the idle will increase by as much as 400 rpm. We checked for vacuum leaks, but found none.We're leaning towards a bad power valve and tomorrow I'll pull the carb and check it but I was wondering if there is anything else I should be looking for? thanks in advance for any tips,,,,,,Mike