That's not right at all. Something is wrong there. The Kouba screw is threaded just like the OEM unit unless you got a bad one. Your description of the Kouba screw not going in loose and having a little resistance is relatively normal. I wonder if the threads in the carb are buggered? Still, the brass fuel screw is usually the "victim" in a crossthread scenario rather than the carb body. Vibration shouldn't be a big issue here, since the carb is mounted between two rubber mounts.

The fuel screw just should not turn on its own. I'm curious about your need for a two steps larger pilot jet.

 

Me too, with the FMF, K&N, a ground header, smog delete, removed snorkel and dyno jet kit with a 24 main, I'm at 2.5 turns out on the stock pilot... and I still get a good amount of decel pop with no throttle.

 

Yeah make sure they are in the proper order: O-ring, washer, spring, then the Kouba screw.

Kouba states that it can and will vibrate out if turned farher than 2.5 turns out.

 

I can barely turn my Kouba screw by hand it's so tight.