The FG-20 has an inhouse Saito carby (rather than a Walbro) that uses some sort of membrane pressure. The result is that is can't transfer fuel over much of a distance. 20cm is probably about as far as you can do assuming the carby is roughly at mid-tank level (eg not pumping uphill).

I'm using black fuel tubing so I can't see if the fuel is flowing or not, but experience has taught me that ifthe engine has been running fine and then drops off, try a new spark plug first and then check the fuel set-up.

As you know, the engine is fiddly to tune and even a few clicks can make a huge difference. The low needle influences most of the throttle range. I generally find it best to run the low end a little rich, which then enables the high end to be leaned out 4 or 5 clicks more. Of course, too lean (top end) or too rich (low end) and the engine will usually die at the worst time (eg WOT on take off). I found the best way to tune (both low end and high end) was to hold the plane up to the sky and tune each needle accordingly at idle and WOT (engine dies it is too lean, engine splutters too rich).

I currently have my FG-20 in a VQ 2.7m wing span Pilatus Porter (6.5kg total weight). It ran perfectly, but I changed the fueling set up and it took me ages to get it right. I must have dug the fuel tank out of the belly of the plane about 4 times to check/replace and check things again and again. I had a succession of small problems (all adding up in difficulty in getting a good flow of fuel to the engine) which I finally fixed up. I've had the equivalent of about 5 hours good engine operation since that time. The engine economy is amazing (about 1 hours flying from 500ml of petrol).