Hey all got my old 250 crossflow running. New fuel pump
, filter, leads, plugs, cap, new carby and set.the timing to factory specs at 4degress btdc. It has a big flat spot when u throttle to much. Backfires and blew my muffler to pieces. Any ideas on what the cause could be. Had a mechanic look at it and he was stumped.
Pcv valve is missing. Redone all the hoses as per manual. All vacuum on egr advanced timing and what not hold vacuum. Can feel it when u suck on the hoses. Not sure what is a main cause for it. 1978 250 crossflow.