fellows worked on a 26 HP B&S 445877, it was surging real bad at Idle, removed the carb. cleaned, replaced, no air leaks, its better but still has some slight surging, running it without the air filter, might have to tear it down again, any guessing, thanks, Light Mechanic

If it didn't surge the last time you / the customer ran it before storage, than it's probably just in the carb. It can be due to other problems, but unlikely.
If part choke make the surge stop, you've diagnosed it.
Paul

If its just a slight surge at idle, then you can try using an engine additive such as sea foam in the gas, I have used this product many times to fixing slight hunting issues and it even unstuck the fuel injectors on my truck :)

fellow is sat for several months at my daughters house, went to cut the grass cause her and him split ways, put some fresh fuel it started up run good at high speed but would surge when throttled down, so I removed the carb. cleaned it, not really anything in it that I could find that would stop it up, set the vavles, governor, put it back on and it is actually worse, not leaking on the intake, stopped bya shop and asked the best mechanic there, he said that they usually change them out, even some of the ones they get new will do that, I am not a parts changer, might take it down again, been working on them for over 40 years as side line money, they are are a lot cheaper built than the days of the Clinton, Lawson and old briggs, will let you know if something changes, thanks for the help, Light Mechanic