Oren wrote:

Surging engines often is because of improper air / fuel mixture.

Someone said it is likely surging due to clogged fuel passageways, which
makes sense because the air passageways aren't clogged.

If it's the clogged fuel passageways, it's likely because I don't start
these engines for months (sometimes years) at a time, where I leave the
fuel in them (sometimes I pour it out before use if it's really old).

But I wonder why it surges due to clogged fuel passageways?

If the passageway were VARIABLE in diameter, I could see it surging, but
it's a fixed diameter. So even with a clog, it's still a fixed diameter.

Anyway, once I have the word "surging", I can start Googling for Surging
Honda GCV 160, where I see it's a common problem but nobody seems to know
why.

http://www.lawnmowerforum.com/showth...ng-Honda-GC160
https://www.bobistheoilguy.com/forum...Number=1867275
http://www.lawnmowerforum.com/showth...CV-160-surging
http://www.hobbytalk.com/bbs1/108-sm...g-problem.html
https://www.bobistheoilguy.com/forum...1888530&page=2
etc.

It seems most people clean the carb, where there's no harm in that, but
nobody knows why it surges.

They say the orifices are small but that in and of itself can't cause
surging.

Something has to be VARIABLE for the surging to occur.