How to set timing on mid-70's 7.5 hp

[bdmorningstar]

I've rebuilt the carburetor, replaced the water pump, and got my mid-to-late 70's 7.5 hp motor running. It's running a little rough, and I'd like to know how to set the timing on it. I've put a timing light on it but can't figure out how to advance or retard it, and would also like to know if it should be timed at top dead center and line with the tdc mark, or advanced to the degree shown. The timing scale (like a ruler), is not on the motor. Thanks for your help.

 

[Chinewalker]

If you didn't do anything to the timing linkage while working on it, it oshould be fine. It is VERY hard to get the timing out of whack on these. Timing advances and retards with the throttle.