Timing-big drop in idle speed when in gear

I had that same problem when I installed a moderate Comp cam in my Valiant. I tried to set the timing by a light but had no luck. I finally tweeked the idle/air screws and just played around with the timming old school style. Finally found the sweet spot. I will only take a little timing adjustment. A little stall converter will also give you the results you want. I just didn't want to take out the tranny to do that. Good luck, Jerry