I have a toro 621E and once started when done cannot turn off with key, have to pull choke out?

SOURCE: trouble shooting electric start toro 20074

Check battery connections, make sure they are clean and TIGHT!
Check the harness where it plugs into the starter switch
Check the harness where it plugs into the battery wire harness
Check the cable at the starter, make sure it is clean and TIGHT
If you need it, you can go to toro.com and enter your model number and download both the Owner's manual and a parts manual if that helps you any

SOURCE: Have a Toro 51990A string trimmer. It starts, but

toro trimer model 51990a part drum with eyelet

SOURCE: Toro power clear 38587 snow blower won't start.

Certified BLOWER EXPERT
This item is equipped with an electric starter, regardless of the age of the gas (Unless there is rust persent in the GAS tank), the unit will many times still turn over. This unit is also known to have problems with its COLD START or start for very cold temperature. This is what I did to fix my same problem. Attempt to move the unit into a warmer climate such as a garage, cover it will several blankets, (These blankets may get gas on them CAUTION), and allow the unit to warn up. When the unit is COLD, the metal inside the unit contracts and is not in the exact same condition as it was when you purchased the unit. Further, warming up the parts naturally will allow the metal to warm up and greatly increase the possibility of an electric start. Please try this option first.

SOURCE: I have a toro 51944 weed wacker. It has become difficult to start and requires many pulls. The choke must be set at no choke. thanks.

overhaul the carby
the problem will be diaphragms hard and not working properly