RooviatorJ

Thanks IBob, Fuel lines all smooth and no undulations or sags. We are currently looking at the filler caps and the stick vents that are part of their design. Our flying coach has suggested there may be an issue with the lower disc component orientation, difficult to explain in so many words, but if proven will elaborate later.

Thanks for all instructive replies. So it seems that this may not be an unusual issue. In summary, it may boil down to minor differences in vent pressures for either tank plus flow conflicts where down pipes join or meet in a header tank. Interesting that Cessna have dealt with this issue long ago! On further observation of our Jabiru, it seems that it is always the starboard tank has the priority to empty, sometimes there is little difference, sometimes a lot! The assumption and the testing while safely on the ground is that even if one tank completely empties in flight, there should be nothing stopping the other one to take over once there is no "competition", but it would be comforting to have a way of monitoring this when in the sky and maybe even over water! On another forum, the issue of keeping the skid ball in the middle is also often mentioned, but other than this producing different air pressures on the wing-top stick vents, I cannot see that this would cause the big differences we have noticed, especially as on our Jab, there are built in tank vents linked down to the header tank and most of the time (at least) we fly with the ball centred! I will update on here if we find anything else.

We have a home built Jabiru 430, built in 2019. We have noticed a very variable and extensive emptying rate of the tanks to the point that one may not empty at all after a couple of hours flying. We have conducted a lot of ground tests and inspected flows from all the pipes down and up to the tanks, all appears normal. We have a 5 litre header tank fitted. We cannot find an explanation for this, has anybody had a similar experience?