New To Me 06 Suzuki Eiger

I just bought a used 400 Eiger over the weekend and know very little about it and there was no manual with it. I tore it all apart yesterday to give it a thorough checking and learned a lot. I also have an 07 Arctic Cat 500 with a Suzuki motor. I need to change oil and would like to know what the manual recommends for type and weight. Do people have a preference for synthetic vs non-synthetic? I was thinking about running the same thing I do in my Arctic cat for simplicity, but thought I would seek other owners input.  Thanks.  

my 06 eiger 400 takes 3.3 qts,i use a good grade of 10/40.change it every 6 months.