I went to ride my sled this moring 79 skidoo everst 340. And it is running very strangely. It wont idle and when you rev it it seems to lag behind like i will get on the throttle and it will stay reved for a few seconds. It seems to run alright from mid to top but it wont idle I have cleaned the carb. And my bro checked the spark on the plugs and said they were good. I'm thinking its the timing. Anyother suggestions? It had ran fine a few days ago.