Back in the "good old days" they were all manual and I didn't have any leaking or hear of hydrolocked engines. My other bike has a manual fuel tap and I haven't forgotten to turn it off, I guess old habits die hard.
Regards, Russell
Yes, they mostly all leaked back then ( I carried a small rubber mallet just to wack the carbs) but then again ALL bikes had overflow tubes and they did not have ethanol back then .. Also the problem with manual petcocks is and never has been turning them off. The turning off part is fine.
The problem is turning them ON when the engine is not running and not turning them off the exact second the engine is shut off. You cannot ever be as accurate or as fast as an auto petcock there fore your chances of hurting your engine is greater because it only takes a few seconds of FULL FUEL FLOW to hydro lock the engine and a manual petcock is always at full flow when turned on.
Automatic petcocks when they fail (if they fail) only ever dribble a small amount of fuel so it takes a much longer time typically all night to fill a cylinder. Proper maintenance or periodic replacement means the auto petcock will not leak and auto petcocks do not flow any fuel when the engine is not turning. Your manual pet cock cannot do that, they flow full out when the engine is not running when you turn it on (and most people turn it on before starting the engine). It only takes 3 seconds.
Overflow tubes are the only true protection from manual and defective auto petcocks (with leaky float valves). Floats valves do leak occasionally, they always will, they always have. Most times you would not even be aware unless you have overflow tubes. It just shows up as poor fuel economy.