How to ajust the timing chain on Yamaha big bear motor a tv

You will need to find the timing marks and have the firing specifications to line it up. Most timing marks have the Top Dead Center position marked with a large raised triangle mark. Take out the spark plugs and use a pencil with an eraser to determine (by feel) when the piston raises all the way up the cylinder... this is the TDC position. Line up the chain so that the TDC triangle corresponds to the actual piston travel inside the cylinder. Once you have them aligned, dial back the timing the few degrees specified in the manual. Put the plugs back in and fire it up. It it sounds "off" then repeat the process, something wasn't aligned correctly.