Got the right tank prepped and primed this morning. Forgot to mask off the areas on the back baffles for the zee brackets, but just cleaned the areas with acetone after painting.
9/11: sealed up the back baffle this morning. Broke my rivet puller on the last rivet.
9/14: finished up the final countersinks and rivets in the right tank. satisfied that the left tank was holding I moved the balloon and schraeder valve over to test it. Looks like it's leaking around the fuel pickup. I removed it and put more thread sealant on and reinstalled. Still leaking. Hard to tell if it's the pick up or through the skin adjacent. Pretty sure it's the pickup.
9/15 am: removed the fuel pick up, cleaned it all up with acetone and resealed it with a healthy bead of loctite 567. Re-inflated the balloon and it seems to be holding.
9/15 pm: balloon was deflated when I got home. :(
I can't find the leak and getting frustrated. My wife casually mentioned that those are really cheap balloons I was using. And I had reused the one from the left tank. Could it just be the old cheap balloon slowly leaking through the skin? I replaced the old balloon with a new one and it seems to be holding. I also inflated the old balloon and ties it off; in an hour it had noticeably deflated.
Lesson learned - don't use old balloons.
9/25: have been chasing a slow leak for weeks in this tank. Balloon holds for 2 days, but slowly is getting smaller. By the 3rd day it is completely deflated. So am I. Can't find a leak anywhere.