thought i would post some pics in whats involved in checking your ignition timing, this is an ohv, but will also work on flathead, but you will have to pull the head to find top dead center, as a piston stop which i use wont work with a flathead!
the tools you need to have, an old inductive timing light, a piston stop, and a small degree wheel, the one i use came from comp cams!
next i take the nut off the crank, and put the degree wheel on and tighten the nut back down, you may have to pull the tinwork to do this!
next using the above piston stop, pull the sparkplug and turn the engine by hand till the piston is almost to the top of the bore, i use a small screwdriver to feel where the piston is, make sure engine is on compression stroke, next install the piston stop and turn engine clockwise till the piston touches the stop, DO NOT USE STARTER FOR THIS!
now using a piece of stiff wire, bolt it down somewhere on the block, doesnt matter where, i used a starter bolt, bend the wire so it points at a number on the degree wheel, in this case, it points to 140 on the degree wheel, write that number down,
now turn the engine counter clockwise till the piston again hits the stop, and write down the number your pointer is pointing at, which in this case is 178,
now halfway between 140 and 178 is gonna be true top dead center, which is 159, so pull the piston stop out and turn the engine clockwise till the pointer is exactly on 159, this is top dead center!
now we need the pointer to be on 0 on the degree wheel, you can either move the degree wheel, being careful not to turn crankshaft or simply make a new pointer, making a new pointer is much easier, we dont want to move the crankshaft whatsoever or readings will be off, now that you have the pointer at 0 on degree wheel, reinstall the sparkplug, hook up the timing light, start the engine and point the light at the degree wheel, the pointer will show you exactly how many degrees the sparkplug is firing before top dead center on the compression stroke!!
i tried to get a picture of the timing light showing the degrees on the flywheel, not an easy task and finally gave up!!