The first thing I'd do is get new plugs.

My guess though is that you're timing is off. Easiest there would be to slowly turn the distributor while someone is cranking the motor. It'll hit when it finds its happy place. Assistant under the hood turning the distributor should be prepared to get shocked. Try to avoid leaning on the fender or touching the car anywhere else when doing this...

Could also be a fuel issue though. For that, pour a small amount of fresh gas down the throats of each carb, replace filter to avoid fire should it backfire, then see if it hits. A fire extinguisher on hand wouldn't be a bad idea just to be safe...

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-Matt I ♥ my ♂