ANOTHER 760 issue

[kirkp]

Relatively new to the forum and have a question about my 760 rifle.  It’s a 5th variant model that was given to me by a friend.  I installed a scope and started zeroing it in when I noticed a problem.  Most of the time when pumping it up there is back pressure and the pellet fires normally.  At other times there is no back pressure felt when pumping it up and the pellet stays in the barrel.  Luckily I can eventually get it to pump up normally and get the pellet out.  In looking at the piston it appears well oiled although with what I don’t know.

I assume that it’s one or more seals that need to be replaced unless anyone else has another idea.  I was looking at the Crosman parts list and see that they list a seal kit consisting of a breech gasket, pump cup and valve assembly.  I also see that they have two o-rings that go on the valve body which I assume come with the valve assembly.  Is there anything else I missed that might be causing the problem? 

I appreciate all your help.
Kirk

[longhunter]

try cocking the gun before you pump it. the valve spring could be weak and the hammer is holding it open, thereby allowing the air to escape as you pump.
you may also have a bunch of gunk in the valve. that will require disassembly. might not be a bad idea to tear it down and clean it up anyway.
if it were me, and there was a question of what the gun has been lubed with, i'd tear it down and clean the whole shootin' match. then, re-oil with either pelgun oil or good ol' tranny fluid.  hope this helps.