Those particular engines did have valve sticking issues sometimes.
Either remove it and clean the carbon off it, paying particular attention to the guide area or just replace the valve as they are relative inexpensive.
As mentioned do not hit it as the compression release tab on the cam is easily broken, then you have a complete tear down for cam replacement.
And yes, the compression release is holding the valve open .010 give/take on the compression stroke till the very last few degrees of rotation BTDC.
then it closes jast as the ignition fires the plug.
At anything over cranking speed, the centrifugal force causes the tab to
become inactive allowing full compression.
simple mechanical design and it works well even in todays 'lectronic excesses.
It might be noted that a guide reamer works well cleaning valve guide as carbon also and sometimes, contributes just as much as a carboned valve stem.
Lacking a guide
reamer, a drill of the correct size used by hand
can work but carbon is hard.
IIRR 5/16" is the guide size but various engines/sizes/manufactures use other guide sizes.
-----TMI (too much information)