How well is the tank foam rubber padded? That could be a source of air bubbles. A fuel filter before the carb will tend to condense air bubbles and help with that as will a sintered clunk.

Having the clunk go to the front of the tank is inviting a kink in the tubing or getting it stuck in the front where it doesn't usually belong. I have a bad habit of getting the clunk stuck in the front of the tank sometimes after a hard landing and then forgetting to check for that! (ask me how many dead stick landings it takes for this pilot to then realize the clunk is stuck in the front.....

Ernie Misner