I have been having problems with the old Blazer and do not know if it is the Carb. or the Dist. It will run fine then all of the sudden it with stumble on aceleration, and if I give it more throttle it will pop up thru the carb. If I feel it start to stumble and keep it at the same throttle it will stumble for a few and then recover with a slight surge and run fine untill the next time. The only thing I have done to try and correct this problem is replace the fuel filter and spray some carb cleaner in it. At first I thought it could be my vacume advance but it does this same thing at idel. Any ideas???