Hello, I have a 20.0 HP, 42'' mower; the engine starts and everything... it runs as long as the clutch/brake is being applied, but as you start removing the clutch/brake EVEN IN NEUTRAL the engine stops..
so the engine works but stops as you remove the clutch/Brake

by the way it has a semiautomatic transmission

Model No.= 917.271920

any idea of how to solve the problem?

thanks for your attention

Sounds like the brake switch is bad. I believe it is located under the fender at the brake rod. To test, jumper switch out and try. If that takes care of problem, replace switch. It is for safety reasons. Never leave a safety switch bypassed. I know John Deere, but believe this is right for Craftsman

Well Yes That Is Correct, Although I Have Bypassed Many Times For Diagnostics, I Have Never Told Anyone To Do So.

It may be a simple solution. If it has a deck that can be raised and lowered, raise the deck and try again, if not pull it on to a flat hard surface try that, if it still does not start it may have a grass build up underneath the deck. Tip your mower just enough to see underneath it and support it underneath the frame not the deck with something that will hold the weight. You may have a friend help. Do not place your hands underneath the mower use a stick and nock off the grass around the edges of the deck. Other wise the mower may have thrown a belt and it is jamming the works.

Check safety switch on seat, maybe stuck

I believe travmyfld has the correct answer.