Egads, that is what mine looked like when I bought it at a yard sale in 1984 for $200. Then I think I put another $100 or so, and that saw has been a faithful friend ever since. I don't use mine commercially, but it cuts 6-chords of pine each year. I made an adapter to mount a Green-Weenie air filter on it because the original air boxes just seem to leak too much. I fired my 2100 CD up a few weeks back to quarter-up some 38-inch Digger Pine.
I wonder if wrestling those big rounds will keep my back tuned-up for winter snow skiing forward-tumbles. hahaha
https://tillotson.ie/wp-content/uploads/2015/07/techinfo_hs_us.pdf
My one suggestion is to check the crank-case seals. that was the only thing I did to my engine. I cannot remember if mine is a thin-ring, but I have never changed the ring or barrel the whole time I have owned the saw - 34 years already. I have rebuilt the carb numerous times. And, this aboristsite is where I learned how to block-off the Governor, which I have not yet done, and should.
Can the Governor cause over-fueling ? I say this because until I fine-tuned the L and H adjustments, my saw seemed like the governor was kicking in early, and the governor chokes the engine somehow giving it more fuel. I am not an expert, so hopefully one of the guru's will have an answer.
Give that thing a bath and it might run just because it is clean.