Well we dont have experimental in the UK. We have the LAA or BMAA, who are still both very stringent but still much easier to deal with than EASA. Never the less, it is still a pain in the ass and expensive to get anything certified no matter which body certifies it. And you are lucky to escape the UK. I would leave tomorrow if I had the chance. I spent several years living and working around Boston, Chicago and upstate New York.....and I really would go back tomorrow if I had the chance. Of course there is the small mountain of convincing the Mrs that its a good idea.
right....so I found a perfect fit from a tractor parts supplier in the UK. and it was mega cheap at £6.50.....about $8. a bit of 1/4 inch copper fuel pipe and a drill bit and it was soon modified with a vent tube.
Interesting that with regards to yaw axis you say it flies straight hands off.....yes yes I know your feet are not hands but I assume you mean feet off as well? I find it interesting as you don't appear to have a rudder trim tab. My MkIV has a rudder trim tab that is almost 90 degrees bent over!! and still requires a bit of boot to fly straight.
So finally got round to some ground runs yesterday (after finding a new fuel cap). I think the Mikuni pulse pump contributed to the failure. Turns out at idle the fuel pressure was right on 0.2 bar and at full power was flickering just below 0.2 bar. With the Facet pump on pressure was up at 0.4 nearly 0.5 bar. So as soon as I switched off the facet pump and at full power the Mikuni was not enough to deal with fuel venting back out over the wing. Doesn't explain why switching the facet back on did not restore flow though.
ok, I have 1 tank. I have a stop cock between the main tank and the header and I have a bleed valve to drain the header which is what I assume you are all calling a vent? part of my pre-flight is to bleed/vent the header for 10 seconds or longer if it needs to clear air. Once I was back on the ground and prior to loading on to the trailer I needed to drain what was in the tank as it was sloshing out the wing when they were folded. So I stuck a jerry can under the header tank and opened the bleed/vent valve.......it to quiet a while gurgling and bubbling and filling up before it started to bleed out the bottom. Oh and I also have a fuel stop cock between the header tank and engine...roughly where the flapperon lever is.