Thunderbird 900 - Fuel Tap Question...

If you leave the petrol tap switched on, then the only thing preventing a tankful of the finest unleaded petroleum ending up either on the floor or in the bike's engine is the efficiency of the float and its valve in the carburettor. A bit of muck or gunge preventing the needle valve closing properly, or indeed a punctured float (unlikely and would lead to poor running anyway) could easily cause a sump full of petroil - which is fine on a 2 stroke (well, not really - not a sump full - but you see what I mean) but highly detrimental to a 4 stroke engine.
Thankfully it never happened to me, back in days of yore before vacuum fuel taps and fuel injection, but my mate's early CB750 suffered that fate overnight, which cost him an oil change and a day off work. Good job he didn't smoke!!!!

 

Just turn it off!! How long will it take?

 

Just remember to turn it back on again before you ride off. When I was a lot younger my first H***a had a fuel tap and many's the time I sputtered to a stop after half a mile, swearing, turning it on and kicking the thing over several times to draw enough fuel through to start it again. Good job it was a weedy little 2-smoke 100cc. Got quite good at checking the tap on the move as soon as it coughed though .

 

I can imagine that would be a good move if you were going to lay the bike up for a while, assuming it was a faff or you were unaware of how to drain a float bowl. Got no idea of how that sort of thing works with current FI throttle bodies so I'll, er, defer to others on that one and not worry.