10w30 0r 10w40 both seem to work well.
To Determine what spark plug is in your 16hp enging you would need to be more specific. It could have a Briggs and Stratton engine or it could have a Kohler engine. Both engines use different spark plugs. The spark plug for the Kohler engine is part number 32295-1. The part number for the B&S engine is 43591-7
gas is not going to the motor
on the enging
in enging compartment
It is broken.
Google and yahoo are the largaest search enging.
Time to replace enging oil
enging spere parts
It is not an interference engine, in spite of what some say.
It is inside the gas tank.
Put in your friend name in the facebook search enging and click on search.
Not a requirement, but a very good idea if you plan on keeping it for a while.