I have an Snapper 8hp snowblower that's getting on in years and right now it only runs fully choked. I imagine it's all in the carb. Do the needle adjusters slowly lose their adjustment, because it was running fine last year and gradually needed more choking?

Hi,
No the adjustment needles should not move out of adjutment if all pieces are there. The needles should have a spring, a washer and a sealing o-ring on them in that order. The spring holds them in place, the washer protects the o-ring from the end of the spring and the o-ring seals the jet.
More likely is the slow accumulation of varnish or some contaminate in the fuel.
Peace,
Clarke

If you have the time just add some SeaFoam carb cleaner to your gas. Over the next tank or two your problem will go away faster than it appeared.