As racerone states, the carburetor needs cleaning. Adjust after cleaning as follows. Info for replacing the m/starter cord also follows.
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.
Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.
Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.
When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
(Manual Starter Cord Installation)
(This pertains to the vertical type of Manual Starters such as the 9.5hp and later 4.5/6/8hp models etc)
(J. Reeves)
1 - Have a pair of vice grips handy set so that they will grab the top of the starter spindle tightly but will not damage it.
2 - Using a large screwdriver inserted into the top of the starter spindle, wind the starter in a counter clockwise direction 12 to 14 turns, stopping so that the cord locking slot is facing the away from the engine.
3 - Lock the spindle in that position with the vice grips, letting the vice grips lay against the flywheel.
4 - Insert the cord as needed and make sure it is retained properly at that slot.
5 - Feed the cord out the starter cord hole at the front of the engine and attach the handle.
6 - Grip the cord tightly so that the spindle cannot spin around rapidly, then release the vice grips.
7 - Allow the cord to be withdrawn slowly around the spindle.
