There are 3 different types of carburettor that could have been fitted to this engine but none of them have any adjustment to prevent hunting.
What is happening is the govenor is allowing the engine speed to increase to a level where there is not enogh fuel so it slows down.
The govenor then opens up the throttle to maintain speed and the engine accelerates then gets to a point where there is not enough fuel so it slows down again.
There are 2 ways for the engine not to get enough fuel.
1) blockages in the carb preventing the full flow of fuel
2) air entering the cylinder after the carburettor
So pull the cover off the engine, remove the carburettor and clean it properly, if you are not sure exactly how to do it then ask.
An overhaul kit will not hurt nor break the bank.
Also check that long manifold tube they come loose and I find lot of them are actually cracked thus leaking air.
Replace the gasket and be careful when you tighten the two very sall bolts as the threads are easily stripped which is why I like to fit a new gasket.
The seal between this tube and the carb is done via an O ring andis easily damaged so replace it as well.