This has me baffled, totally and completely but I’m probably not that smart either!!!

57 GMC 1/2T with a 261 and a push button start

After starting and if it only runs for a very short time the engine can be shut off by turning the key to the off position, if it runs for any amount of time it won’t turn off and I have to choke it to kill it


Any ideas are most welcome

Thank you so much!!!