You say you've replaced dizzy cap and rotor arm etc (things in my experience never cure a prob) but have you checked cam to crank timing as previously stated? Go back to basics and check this first, then if you have a timing gun check the ignition timing, including advancing. Prove a good spark on all plugs.If these check out check compression on all cylinders, has the carb been fully checked over for leaks and function etc? Spray carb cleaner at suspect gaskets on/around carb when running to see if affects revs. If timing, spark, advance and compression are ok then it kind of must be a carb/ fuelling issue, and if you don't know how to set a carb engine up you may have to take it to someone who can. Don't get too stressed because it takes longer to sell a broken car for nothing than it does to think methodically and find the problem that is right in front of you. A good carb tuner can transform a cars performance to differ night and day, trust me I've been there with the 1.3 pierburg pile o sh!te
