Hey. I have recently aquiered an old Yamaha Venture RS, but I have problems with getting it to start. It ran yesterday, for the first time in a long time. Had to charge the battery, but after that it was fine. Then when I tried to start it today, it went on, I let it run for some time and then it died. Had to change the sparkplugs, which I did, and once again it started. Let it run a little more and then it died again. Battery, fuel hose and sparks has been checked, as well as oil, gas and coolant fluid. Any idea what it could be? Im completely new to Snowmobiles and engines, so would really appreciate some help.