So long as you use the same point for both marks it does not matter what you check against. With my twin, with a competition tank, you can see the top fin even with the tank on. If you have a road tank you might not be able to see the top fin easily with the tank on for a subsequent timing check.SOHC wrote:I was having brain fade there for a wile, I made a rod and marked off the top fin,
When I measure 11/32 off the piston and then check my degree disk it still comes up at 39 degrees BTDC
Worth checking the timing on both cylinders too as the magneto ring may be a little worn ( assuming you have one) and you may need to set it at a compromise to get the two cylinders firing at their best.