the easy way of checking is very simple on port timimg and this means you donot have to find top dead centre, i hope you have a degree wheel , your move your clutch and mount your degree wheel on the crankshaft, i use a piece of plastic pipe that fits over the crank and the degree wheel fits tight over the pipe , take some solder and wrap it around your studs that hold the bar on , flatten the end of your solder so it is a marker for your degree wheel, so let say we are trying to find our ext. port timing
bring your piston down until it just start to open your port , watch as carefull as you can on the port opening, set your degree wheel at zero degrees now roll your motor down and back up until your port is as close to closed as you can get and still see the top of your piston or light comimg threw the port , now we will say your degree wheel says 160 degrees , so divide that number by 2 because you went up and down so now you have 80 degrees of port opening, now if you want to know how many degrees from top dead centre , in one direction you have 180 degrees so take 180 degrees and minus your opening 80 degrees and you have 100 degrees from top dead centre before your port starts to open, very simple and alot easier than having to find top dead centre all the time
