When i try to start the riding mower will only crank once.....toro 16-hxl will crank once, then nothing

Check with a Toro dealer or directly by contacting Toro.

Your fuel needle is not closing , allowing too much fuel... there needs to be a proper fuel air ratio. Have you recently had the unit serviced? Someone mess with the carburetor itself?

The float needs to be adjusted so it closes the needle sooner

If you jumper across the two main solenoid terminals and it starts then replace the solenoid; otherwise it could be the starter.

if it has flat tires your thinkig its not disengaging but it is it does not want to roll on flat tires shove it back and forth till it rolls once you have tranny disengaged nothing holds it that should get you home then we can work on the rest

There 3 ways. One take off lug nuts like a car.
Two have a rubber cap, remove a remove e-clip.
Third,there a nut to remove.

...... you will find the newer 38" decks are a very close match up.

If you are jumping it thru the battery and it starts, then chances are that your battery needs replacement.

The spindles on the deck may need replacing.Thanks for asking and I hope this helps out.Please leave me 4 thumbs up.

Locate the model and serial number tag, under the seat.
use the site www.toro.com to download pdf of manual

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

simple go to outdoorpowerequipment.com and enter make and model and you can download or print it in pdf form