fourtrax hard to start

hi! I’m new here! I’m trying to help my father with his 1990 fourtrax 350. We got it new and has been very reliable. But now, if we don’t use it for 1 day, it will not start. The engine cranks, has spark but no fuel. If I remove the plug and pour some fuel in the engine, it will start right away and will be fine. I can shut it down, restart and drive all day without any problems. I don’t have access to it at the moment, but I’ll check it out when I go there next time. I hope you guys have some hints for this strange problem. thanks for your help!