If you ever have to leave your Grasshopper zero turn radius lawn mower outside or any other lawn equipment you should always cover it with a tarp or some kind of protective cover. If it gets rained for long periods of time then water can seep into the engine and fuel system.
The best thing to do is to perform a full maintenance on the lawn mower. Remove the battery, drain and replace the oil, replace the oil filter, and clean or replace the air filter. You should also drain the gas, change the fuel filter, clean or replace the spark plug, and put in fresh gas.
Try letting the lawn mower warm up for a little bit before giving it full throttle.
The model and serial numbers on your Grasshopper zero-turn mower will be found in different spots, depending on the model:
On FrontMount and Midmount mowers they will be to the right of the frame, under the seat.
On FrontMount Decks- on the back of the deck, to the right.
NOTE: if you need a part for the small engine in your Grasshopper zero-turn mower, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Grasshopper mower. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: