Go to outdoor power Equipment site and read the sections on Honda carb cleaning.
Your carb is not there but it will come apart exactly the same way.
Then remove the fuel tank and clean it out as well
Take photos of where everything is before you pull anthinf apart and mark the throttle cable so you can get it back in the same position.
Your mower is surging and surging on a doverned engine is always due to insufficient fuel to run continously at a particular speed.
@ causes
I not enoug fuel getting in ( dirty tank, fuel lines, carb etc )
or
Air entering after the fuel has been added ( broken gasket, loose carb )
