I have my engine back together, but it is only firing on 4 cylinders and I do get flame out of the exhaust. (looks neat, but totally useless) From the heat on the headers, it is 5 7 3 and 4 that are firing. 1,2,6 & 8 are cold. I have rechecked the plug wires and I am getting spark on each plug and the order appears correct. My first guess was reversed wires,but the order matchs the diagram and firing order. Any ideas ?