and yes usually a bike will run if the jet is too small, although if its WAYYYY too small it wont. i actually own a 39 dellorto jet for some reason, and pretty much no bike will start with that jet.
if your jet is too small, its true, youll run lean and ruin your shit, but also keep in mind that the engine generally wont seize unless you run it way too lean for like 10 miles or more, thats my rule of thumb. not to say you SHOULD run a bike super lean, but dont get all scared when you're testing out jetting or doing plug chops.
ask me how i know this