Try watching the video in the link below:
There is no way to adjust the timing on a 17.5 Briggs engine. The magnet is on the side of the flywheel and there is only one way the flywheel can line up. All you can do is make wure that the coil is gapped correctly.
You do not state if it is a single or a twin (which it could be of either at that HP) so links to each below:
Lawnmower. It's a Briggs & Stratton engine.
what grade of oil on this engine
Briggs & Stratton
Briggs has a rudimentary wiring diagram for the operation of an electric start engine. see the link below.
SAE 30 weight.
why does my 4.75 BRIGGS & STRATTON lawnmower engine idles high and low when cutting my grass
You adjust the run and idle speed with the governor wire...loosen the nut and adjust it.
The correct gap for the spark plug of a Briggs and Stratton 6.75 Lawnmower engine 0.030. Most new plugs come with that gap, but it is best to check to make sure.
It is 0.030" for an L-head engine.
My engine is idling too high. How do I adjust the idle speed?