If you have never worked on a four stroke engine you should get one of the books about them. Istill have my trusty OLD A Guide To O.S.Model 4/Strokes written and illustrated by Graham C. Rice. Some of this little book is out dated but only because of some of the newer minor changes that have been made over the years. The last time it was updated was in 1999. It's from RCM Anthology Library Series, it was only a couple of bucks and well worth it.
Ihave found much better books at one of my LHS book racks and should up grade my reading. This little book is great to help understand what is inside one of these engines but doesn't go into trouble shooting, has nothing on pumpers or pumps.
Your fuel pump either pumps or it doesn't pump, not a lot of gray area here and it is a replacement part, can't be rebuilt. If it's a regulator problem it's a send into O.S., this is one of my sore spots with O.S. they will sell you a new regulator cover but will not sell you a diaphram, you have to send in the complete carb to them over a 50 cent part.
Go to the glow engine forum and you can ask Bill Baxter of O.S. about engine problems, the man knows his stuff and will answer you back pretty fast.