That looks like a Homelite check valve. The Poulan ones are PN 530026119. You could stick the one you have on it on with a bit of Motoseal. Just don't plug it up. If there's room you could also wrap the barb with a bit of Teflon tape.Thanks Tim! Another question that has to do with the 4200. The duck bill piece that goes on the end of the little breather screw keeps falling off in into the fuel tank. Is there any way
to keep it from doing that? I think the duckbill piece is actually for a different saw. Here is a pic.
View attachment 376749
It needs to be a snug fit so it doesn't leak.