Run some fuel injection cleaner through it with new mixed gas.
For the money, price out a new carb. It is probably less money than paying someone to "attempt" to rebuild yours and would only take a few minutes to change.
I ain't skert of Jake........ I am old and he probably feels sorry for me.
other sources of poor performance
Depending on how long it sat, the diaphram for the fuel pump can get soft or get pinholes and cause poor performance too, an easy and cheap fix if that's it.
And thsi may be obvious, but check the oil mix ratio....some will vary and a thick mix will cause fouling and boggy power issues.
A good clean out of the tank also helps, even after devarnishing a long stored motor, other areas with bad gas can sneak in and redo the problem all over again.
I'd start from the tank and clean/replace what is needed to get it a clean fuel supply.
Also check the air intake...mousenests and other stuff can choke that up resulting in less than ideal power.
Some of this m ay seem obvious and you probably did most of it, but it's amzing to me how something as simple as an auger motor can get mucked up by even simpler things, I feel your pain.
Hopefully that's it
should just be two screws and getting a replacement (it's just a rubber diaphram that you will of course want to put in the right way....but it's only got two ways so it should be easy.)
Best of luck.
If you're ever in the valley, Homestead Garage does terrific small engine work. we send all our auger repair referrals over to him, with never a snag.
I use Strikemasters. I send the powerhead back every second or third year and they go through it and fix what needs fixing for a very nominal fee. Turnaround time is pretty quick too. I recommend you call the manufacturer of your auger and ask if they have such a service.
My auger is an old Mag 2000, maybe 9 years old. Still works as well today as it did when I bought it.