1986 Polaris Sprint 340

I got this sled last year for free , it wasn't running when I got it , I put new gas lines on it and it started after awhile of priming and pulling . Last night I took it out for the first time this season and it started off very slowly but once it got going it seemed to have no issues , when I got it , it had been sitting outside for about fifteen years and had bad oil and gas , the first time I ran it it seemed like the oil reservoir wasn't emptying at all , turns out it wasn't I ran it for about ten hours last year and the reservoir never seemed to go down , so now I have cut the oil line and I am just mixing oil and gas which seems to be working . My question is , is there anything I should adjust/clean to make sure it is ready for this season . I am new to the snowmobile world but I have some experience repairing ATVs , dirt bike and our sxs . I am planning to get a new belt soon so is there anything other than that , that I could do to improve the performance of the sled , thanks in advance

1986 Polaris Sprint 340