Setting timing with a vacuum gauge is about as accurate as sticking your hand out the window into the slipstream to measure road speed instead of using the speedometer.
With the valve cover removed, watch the last valve in line back by the firewall (#6 exhaust). Turn the engine clockwise from the front until that spring is fully compressed, then continue turning until the spring relaxes. Just as it reaches the full-closed position, the next valve in line #6 intake) will start to open. At that point the #1 cylinder (NOT #6!) will be at the top of the compression stroke, ready for the spark plug to fire. This is an absolutely foolproof method of determining which cylinder needs to fire as the BB lines up with the pointer. The crankshaft on all 4-stroke engines turns twice in a 4-stroke cycle, so the timing mark will line up twice- - - -once on compression, and 360 degrees of crankshaft rotation later, at the top of the exhaust stroke. The spark plug needs to fire at the top of the compression stroke.
Jerry
