some bubbles can be expected in certain situations while others may not. i can't answer you there. all i know is that i have not had bubbles sence i got rid of my la and all my planes have flown fine. however, it may be acceptable. if your engine runs fine, than they are probably acceptable. it is a common mistake to overpack tank compartments with foam, so i wanted to throw the fact out there because i do not know you or anything about you, so you may or may not have known.. i appologise if you already knew that. i do not intent to act like i have all the answers. i appologise if i come off as a know it all. i am merely providing suggestions, ideas, and answers because that is exactly what you asked for. becuase i do not know your plane, engine and stup i can not really answer your question. it is in your best judgement to decide whether the bubbles you see are acceptable or excessive. i do not argue your knowladge of fluids. i do not know you personally, so i can't argue. however, under the right conditions, glow fuel may foam. but, the foam is on the top, so my thinking is that if the clunk is sitting in fluid, it should be sucking up only fluid unless there is a place past the clunk where air is getting in. see what i mean?