Surging usually indicates the fuel/air ratio is wrong, often a too-lean condition.
Keep in mind, too-lean can mean TWO issues: not enough fuel OR too much air.
Replacing or absolute cleaning of the carburetor usually resolves the "not enough fuel" problem. If the engine continues to surge, it's likely getting too much air, a.k.a., vacuum leak. To avoid this, never re-use gaskets, always replace with new ones, and be sure to snug down on the carburetor mounting bolts.
It's easy enough to confirm a vacuum leak. When the engine is running, spraying a little bit of carb cleaner around the outside of the carburetor/intake areas will cause the engine to smooth out briefly when the fuel/air ratio is momentarily at the perfect mix.
Caveat: I work for Honda, but the preceding is my opinion alone.