In one of the vett catalogs I bought a timing light that runs on 2 D cell batteries, I think it cost about $15.00 or so. That might be something to look into. It might solve your problem.

It took the combination of an unsheilded wire and hooking the timing light to the alternator. I seen a post a while back about timing with a vacuum guage. When I tried that my timing was so far advanced that I couldn't even see the timing mark. Does not seem to work on my car. Runs great now,but, it's raining like crazy and it's rained everyday for two weeks. So much for living in the desert.

I had the same issue trying to time with a vacuum gauge. I recently put a hotter cam in and had trouble getting it to run right. After I put the light on I was so far advanced I found why my carb was acting funky because the idle speed was coming from the timing. My carb was pulling fuel passed the needle because the carb wasn't getting enough air.

Both Ken (kstyer) and I have posted methods for timing by vac...   they were similar, yet not identical.  If done correctly they produce great results...   there are a few big things that can screw it up.  leaving  any vac accessories still attached while doing this....  leaving vac advance connected, timing the car with old/original distrbutor springs, etc.  if youre happy with baseline settings then timing with light is fine. 

just a thought here. if it is an inductive timing light are you clamping it the right way over the wire? on my lite it has an arrow as to which way it should go. just a thought.