I can't seem to figure out the problem on this 1981 Johnson 15hp. I went through the carb so I know its getting gas. When I test for spark it has good spark. When I looked at a service manual it said to make sure the terminal wires were correct, no terminal junction on this motor. The timming seems to be off or at least it has the symptoms, I have gotten it to loudly backfire about 3 times now, timing? It has good compression and the flywheel is not slipping. What do you think? thank you in advance for any input.