1989? Yamaha Sno Scoot snowmobile

[tnt]

Bought the kids a 1989? Yamaha Sno Scoot snowmobile for Xmas. 80cc motor. Snowmobile has electric start and back up kick start. Rode the snowmobile for about 1 hour yesterday until it quit suddenly. Drained old gas and replced with new fuel. Cleaned carb yet it would not start. Replaced spark plug with a new one (NGK) and it started right up. Today the kids rode it for about 1 hour again and all of the suddedn the motor quit again. I am getting fuel but seem to have a weak spark. If I use the kick start the motor will start after about 30 kicks- way to many for this guy. Motor will run for about 5 seconds and quit. I will try a new plug tommorrow but am wondering if I should be looking at something else. Plug looks new and not fouled. The snowmobile was working hard between kids riding at slow speeds and pulling sleds. We are using the snowmobile at around 7000 feet above sea level.
Also wondering why this machine seems to smoke heavily for a 2 stroke. It is oil injected and I am using th Yamalube synthetic oil. Could I eliminate the oil injection and premix the gas. There was small amount of gas/oil mixture that dripped form the exhaust when I started it today and let it warm up.

[lazzer408]

This is an old post but I'll reply since no one else did and I love sno-scoots. :) Running any 2stroke at low rpm for long periods of time will cause oil to build up in the crankcase since the engine isn't reaching the rpm needed to efficiantly scavange the mixture from the crankcase. Premixing the gas on some 2 stroke engines, can still destroy them because the crank bearings on these take the oil injection directly. The sno-scoot uses a scooter motor and premixing 50:1 with a good oil is fine. Another thing to note is that I'm not a personal fan of synthetic oil in 2 stroke engines because it doesn't burn like non-synthetic oil might which could also explain why your plugs dont -look- fouled. Once the motor cools down will it restart? Is the gas cap vent clear? How about the float vent? A blocked gas cap vent will cause a vacuum to create in the gas tank as the gas is consumed and the gas won't reach the carb. It's a hose if I remember right on those. It's been awhile. Also check the fuel system for dirt that may be restricting the flow of fuel. good luck.
-jeff