i have a 1968 oliver 1650 gas. it has a knock in the motor at mid throttle on up. everyone on here told me it was most likely wrist pins. but i discovered the spark plug in the number 1 cylinder was loose and stripped. it is a bigger plug so i assume it was drilled and retapped years ago. the compression is blowing right by no matter what i do you can hear it loud and clear especially when you start it and shut it off. this cylinder is where i hear the knocking. could this be the cause of my knock? if i take the muffler off the sound almost goes away but if i put it back on it comes right back. any thoughts?