leaving the foot down on the starter should not damage anything. old Suzuki's have a habit of electrical problems. Othert things with old bikes are stale petrol. it goes off and is no good after 3 - 6 months. also old bikes can have the air filter collapse and block the carby.
check the spark by laying the plug against the head and attaching the plug lead and kicking it over see if it is a consistant and strong spark.
put in a new plug and check again. if the spark is poor and intermittent or not present, you may have a dud cdi box. check all the connections as old bikes can get corrosion in the connectors and the earth points. if all the ancilliary bits look all right, send the box off for testing by a good auto elec who does bikes....
hopefully its just stale fuel....