well im not totally convinced you need a valve yet..
did you make sure the head is on TDC and has valve clearance when doing the leak test?
the gap you see thru the exhaust valve!! do you see the gap all the way around or only on one side?
now here's the bit that gets me, we fog the absolute pi$$ of out a zonger 140 every weekend and have never had a drama like this ever.. (included valve bouncing it all the time)
also going by the small amount your saying the valve is bent means the engine would run fine.. my engine has a bent valve (or 2) and it runs absolutely fine, idles fine, revs fine.
i think more diagnosis is needed, ot take the head to someone that can check it..
also carbon build up can hold a valve open while not running (when running it quickly blows thru and allows the valve to seat).
well if you have some money pull it out and replace it, BUT IF YOUR BROKE AND THE BIKE IS NOT THE BEST BIKE IN THE WORLD AND YOUR NOT GONNA RACE IT AND ETC ETC,THE valve stems on these are very weak and bend very easy right at the base of the shaft, find a socket the size of the valve place it on the face of the valve with it still in the head and tap the socket until the valve seats flush,now before you guys all say bodgie prick i did say BUT IF YOUR BROKE AND THE BIKE IS NOT THE BEST BIKE IN THE WORLD AND YOUR NOT GONNA RACE IT AND ETC ETC,please note i have done this over many years a couple of times with no negative consequenses
i find nothing wrong with this method if the bent valve is only minor..
i have also done this many times in the past, and was also shown how to do this by a pro engine rebuilder.. tho my method is done in a lathe.
the bent valve/s in mine will get the same treatment but i will reface the valves afterwards..