Well, I used to always think that the short piece of fuel tubing sealed something. I had a couple of engines where you could see a large quantity of fine airbubbles being sucked in via a remote needle valve and heading to the carb on the engine. The engine ran like crap, no adjustments worked, false needle settings, too rich or too lean, nothing in between. But after sticking on a piece of fuel tubing, the air bubbles went away and then engine behaved like it ought to.

But in retrospect now, maybe it was just centering the needle better than stopping the air bubbles. so maybe the air bubbles wasn't really the problem, it just looked like it was.

If I get rambunctious, I'll hookup a GMS 1.20 engine with remote needle valve and see if I can take close up videos and pics of the remote needle valve on it causing the problems. Then try it with a piece of fuel tubing and see what happens.

Anyway, the piece of fuel tubing fixed several ASP 61 four cycle engines that I dealt with. But in that case the needle is on the carb and not remotely mounted. But at first I thought it was an air leak, but maybe it was really simply keeping the needle centered better. These engines all use a single detent on the needle valve.

You can see in the video I made of the "Generic" .36 engine earllier where touching the needle valve without turning it would change the engine speed as the needle moved or the throttle barrel moved ever so slightly. It has the single spring detent too. So that might turn on to be a problem on some engines. Including the one I made a video of too.