Initially thought it was spark plug knock as engine runs rough when it occurred. Increase revs a bit it diminishes. Comes & goes. When audible engine puffing smoke increased. Didn’t want to keep going was afraid of cyl damage. So far no smoke from tail pipes so think cylinders still OK, I hope. Will not run again till I see in side the bottom end. All has to b related. Pretty hard to diagnose w specificity
