If there is black smoke coming out of the exhaust on a Yard Machines riding tractor it most likely means that the air to fuel mixture is too rich, meaning it has too much fuel.
If there is blue smoke coming out of the exhaust then oil has probably leaked into the combustion chamber. This usually happens if the mower was tipped on its side and oil leaked out into the chamber. Or it could mean that 2-stroke engine fuel was used instead of 4-stroke engine fuel (2-stroke engines require an oil and fuel mixture, where as 4-stroke engines do not).
The tag that has the model and serial number of your Yard Machines riding tractor can be found under the seat.
NOTE: if you need a part for the small engine in your Yard Machines lawn tractor, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Yard Machines tractor. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: