9 Hp Briggs Vanguard

[StarTech]

The key to remove if they are not too overly stuck is the straight sided hollow grind flat blade tip bits. Just grinding the side of a regular flat blade screwdriver will not work as well as it will tend to climb (cam) out.

 

[Hammermechanicman]

I have a set of hollow ground gunsmithing screwdrivers. These are great for removing jets. Better than grinding the edges off a standard screwdriver. If the jet is really stuck i soak it a day or 2 with Seafoam Deep Creep.
While you are buying screwdrivers consider a set of JIS screwdrivers. Contrary to popular belief most cross slot screws on mowers are JIS and not phillips. Those real tight bowl screws just don't fit a #2 phillips but a JIS driver fits perfect