My question is : Do these GMC motors of this vintage (guessing 228 ci) have the same firing order as the Chev 235 1,5,3,6,2,4 ? Is the firing order casted on the block or intake anywhere, like a sb chev?
If it does, then the wires may be in the correct order, but in the wrong place. The engine seems to backfire out the carb, like the timing is off. So rather than keep on trying or pulling the truck to start it, I thought we should check a few things out first.
The next step is to find the compression stroke on number one cylinder and install the wires according to the position of the rotor and firing order.
