I forgot to drain the liquid last fall. What problems can I expect?

 

Ok what liquids are you talking about, gas or water. If it's water then it should have had anti frezze in it so nothing happens when it's not drained.
If it's the gas then just drain out the old gas and add fresh gas. If possible find a place near by that sells none ethenal fuel for far less water and carb. problums in the future.