The other thing that can happen is that the tygon line doesn't let the clunk drop to the bottom of a short tank because it is stiffer. I used a heavy clunk on mine.

Well, Just finished running out the 1st quart of fuel thru my GX40 today. Got to admit to my ineptness at tuning, and the 1st few runs had left me frustrated. Been running a 11x6 APC & had seen 10,000 on my tach once or twice, but on transition it seemed to continually want to cut out and idle was very high or it would die.
But today, experimented with the "ignitor" and "pinch" test and played with the low needle and somehow wound up seeing top end at 12,000 and an idle down around 2000. My low speed screw is at 2 turns out and high speed needle at 2-3\4 out. Transition is actually pretty good,but upon restart, the 1st attempt to throttle is "laggy", but after that transition smooths out and seems good to me. I have screwed out the idle stop screw so I can kill the engine using the throttle. Will adjust idle when in plane via radio.
Many Thanks go to Alex and Bill as both have been extremely helpful and patient with me. Now to get to work readying a mount for this horse. Working on a Rascal (clone) and hoping a 12x4 or mabey 12x5 prop. We'll see.

Just keep in mind that you will have to re-tune the carburetor again once you switch to a different prop size.

Thanks for the kind words T-Man.
2-3/4 sounds rich still on the high speed. Make sure you don't have a fuel line pinch somewhere or the idle in too tight.

Bill

Make sure there is no compression leak through the head - drop some oil on the head and check for bubbles.

could you please tell me the fuel mix ratio - ie caster/gas