Hey guys. So the 318’s in our trucks have a plastic tooth timing gear in them. If you are having trouble with a little smoke coming back out the carb and low power. This is not the most favorable place to start but... they do wear and can jump out of time one or two teeth. They will still run but low on power on can let some smoke back out the carb as the valves are no longer closed at the proper degree. Hopefully This is not your problem. But it’s definitely something to think about if you can’t find any other probable cause.