need specifics. look in cavity under tilting seat. get FULL model number. Look on engine for ID plate/decal. get FULL model/type/etc. number. repost.
There are a kazillion l--100 and 17 hp briggs engines out there...

these are the numbers I found under the seat, GLX100A073299 and the tag on the engine the numbers are as follows, 31F7070112E1 and 030430ZE30007. Thanks

Remove the valve cover and watch the valves while you turn the engine by hand (hand on top of engine screen).
Remove spark plug if engine is difficult to turn by hand.
Note how much each valve moves up and down as you turn the engine through a few revolutions.
If one valve seems to have less up and down travel than the other, the exhaust valve seat may have loosened and is now tilted.
If you are not comfortable with doing this, seek the help of a professional shop.

thanks, mownie