1. Shouldn't.

2. Did the clunk get flipped forward on landing? You should be able to remove the line from the needle valve and pump the fuel out thru that line. Make sure that is the clunk pickup line. Sometimes people get the lines switched. Fill tank and the drain completely. If problems occur, remove tank and resolve problem before next flight.

3. Don't believe it really matters but I think dished forwards. When replacing the screw, just lightly snug it down until back of muffler will not turn.(Do not overtighten) Then install jam nut on rear. (This is procedure given me by OS.)