popping can be a few things, older unit carb is not adjusted right newer
units have fixed jets and cant be adjusted, plugged airfilter, misadjust
float level.
those are the simple ones.
major problems is a valve is not seating properly and you get a popping
noise, or the head gasket has failed.
as for the key being sheered no, when sheered the unit wont run. Out of the
1000's I fixed with this problem I can only remember 1 that sheered and did
not change the timing enough so it still ran.
I see you have a lot of posts on here in different groups with different
problems. A cheap and good place for someone to do it them self is a service
manual from the engine manufacture for the model you have. last I checked
they can be bought for under $20.00 but it has been a while. Also the local
library may even have the book for you to read and copy for your self.