Motorcycle Repair: valve problem, vavle, eighth inch

Question
 mitch,
        1974 honda z50 - put in new valves both were bent when i bought the bike,lapped in good.
fired right up.ran it around the block a couple of times.
when to start it next day and would not start. ocassional
backfire through exhaust. pulled head and when i spin cam
and intake valve closes, my exhaust valve will pop open
and sticks about one eighth inch off valve seat. then i
can turn cam back in opposite direction and because of exh valve sticking both valves will be off their seats. when valves are closed they are both seating good. whats  the problem?  thanks for the suggestions!
                      gary
                  runrunningmarathon@yahoo.com  

Answer
sounds like weak vavle springs not pulling rhe va;ves back up to correct seat . they mighr have got hot at one time and weakened ther pressure to pull valves bk up to saey try looking at valve springs then e- mail me bk ok
good luck and keep riding
  
                 mitch kruszynsky