1985 Yamaha SRV 540 questions

I just got a 1985 Yamaha SRV 540 sled the other day and was looking up some maintenance stuff and was wondering if it was a 2 stroke or a 4 stroke. It has a oil container and no place that says anything about mixing gas on sled, just says "Check Oil When Refilling Gas" on gas cap but I was poking around and people are saying its a 2 stroke and to mix gas. Please help. Thank you so much

1985 Yamaha SRV 540 questions