I've had surgeing on my engine combo, with a rebuilt carb and DUI, what I changed was the jet size's were too small, put bigger ones in and was good for about a month, then I found my distributor bolt loose, haven't had another episode since. still try'n to get the most out of it though.
I lean towards the distributor more, it's possible that it's loose or the vacuum canistor doesn't work or is try'n to but messes up timing or a simple spring could be missing. Take a look at it, make sure eveything is working, I would blow on the vacuum canistor line and see if it can hold air, don't suck as those fumes as nasty. then see if the cap is in-tact, and see if you get a steady ignition pulse on each plug by using the timing light on each wire, and last if you still can't find it, see if the plugs are fowled up.
