There should be a governor rod / spring and plate style shaft . Normally the plate should be approx 11:00 o,clock position beside the flywheel . Quite often the rod wears (loosens) and causes surging . You can tweak the plate to increase or decrease Engine Rpm . Also many F-Series Lawnboys had a airvane style governor . The Air vane on top of carb works against the governor rod spring to close the Chokeplate butterfly to maintain proper rpm. The vane also has a small white thumb wheel to adjust back for less front for more rpm ( 3-4 clicks from centre is the norm ) . Proper rpm 2800-3200 max ! P.S. Often crud or rust will cause more spring pressure and cause high rpm . Also a bad crank seal , will cause high rpm , look for oil on crank or blade . I believe you can still download service manuals from Toro.Com Site . P.S.S Governed rpm adjustment is only 50-75 rpm from factory set point .

First thing to check is a common mistake that is easily made. Tip the mower up so that you can look at the governor vane on top of the carb. Make sure that it is placed in the cut out slot in the cooling shroud and moves freely. It is easy to place it on the outside of the slot making the engine run wide open and no amount of adjusting can slow it down.

Next look at the tension spring (yellow box in photo, lower left with a small hook on the end). It should be hooked into a slot on choke slider (Lever F official name for it). The choke cable attaches to it.

The way it should look. Yours may be a little different but they all work nearly the same.

With everything in it's place, hooked up and moves freely. The vane should be close to the flywheel with the engine off. You should feel some tension on the spring when you try to move the vane away from the flywheel with your finger and it should spring back toward the flywheel once released. If no tension is felt. The spring may be broken or not placed into the adjuster wheel correctly.

If everything checks out and is working smoothly. To adjust the RPM. Turn the wheel counterclockwise (toward back of mower) to increase rpm. Clockwise (toward front of mower) to decrease the engine speed..

The small butterfly/vane (inside of carb) connected to the rod that controls speed held in place by two small screws.. ON VERY rare occasions I have saw the vane either fall out or be felt out during carb work... The engine will run without it. But again it will run wide open and no way to slow it down but to shut it off.

The knurled adjusting wheel has a narrow range so that adjustment is not your problem although once you get the air vane right and the small governor spring connected right it will come into play. Quick check; with engine OFF, remove air filter and look into the carb - you should see the edge of the throttle plate - wide-open throttle. Now swing the air vane over and see if it returns under spring tension to WOT. The forced air from the flywheel blows the air vane over to closed throttle unless there is spring tension from the governor. In your case it sounds like the air vane is not being moved by the air stream as 'MM' suggested, so that's where you look first.