You can adjust the valves on your 17 horsepower Briggs and Stratton engine by turning the adjustment screws. The adjustments screws will determine how much fuel goes into the piston chamber.
Try watching the video in the link below.
The valve clearance is set by grinding the faces if there is too much clearance or grinding the tip of the stem if there is too little. If it is a OHV engine you can easily adjust the valves. Try going to the link below for a video that shows how to adjust the valves.
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:
Valves 21 hp Briggs and Stratton Intek V Twin can be adjusted by increasing the torque on screw band with a right rotation. This can eliminate some leaking problems.
Yes They Do
This video will show you how: http://www.youtube.com/watch?v=NjzX-PUjKmo
Even though an Intek is not shown, it would be the YouTube video below.
If it is a Briggs and Stratton engine, it sounds like you might have to adjust the valves. There is a built in compression release that lets it crank over easier. If the valves are too loose it will not release the pressure.
You can not set the timing. It is determined by the keyway between the flywheel and the crankshaft. It only goes in one place. You can adjust the coil, the valves and the carburetor.
The most popular place I know of for instruction is the YouTube site at the link below.
good vid on this on youtube, remove valve cover turn engine by hand till one valve is open"spring compressed, then adjust the valve at rest to .004, repeat on other valve, put a thin coating of rtv silicone on cover and reinstall,