Hunting (recurrent cycling in speed, with a period per cycle of something like 5 seconds) is just about always caused either by lean mixture, or binding in the governor mechanism. If the governor arm will move easily through its full stroke under very light finger pressure, you can be fairly sure the problem is lean mixture. A faulty air cleaner can only make the mixture rich, not lean, so that is not the problem.
Stable, ongoing lean mixture with Hondas is commonly caused by dirt in the fuel system (obstructing the in-tank or in-line filter, or the petrol tap), dirt or gum in the carburetor (obstructing the float chamber needle-and-seat, or the main jet, emulsifier, or idle jet) or a leaky carburetor insulator gasket. You should check all of these, carefully. Split insulator gaskets are very common - many Hondas were built with sticky gaskets that always split when the carburetor was removed, and split gaskets will not seal when reassembled. Remember there is a gasket on each side of the carburetor insulator.
I suggest you begin by checking that the governor linkage is free, then clean the fuel system, then disconnect the fuel hose at the carburetor and check the flow rate of fuel out of the fuel hose into a cup. Then check both of the insulator gaskets to ensure they are not split or leaking.
If you get that far and the problem still exists, it will be time to strip the carburetor and clean it in detail with carburetor cleaner. Refer to this thread:
https://www.outdoorking-forum.com.au/forum/u...p;Words=gcv160&Search=true#Post38602Please report back, either to confirm success, or for further discussion if necessary.
