That little set screw Joe told you about is designed just for that reason. What you were asking about is in the photos I'm posting for you. When I set up an engine that is cowled I like to keep the needle valve hidden and just have a small hole in the cowl. I drill out the NV hole and tap it for 4-40 then use a hex head screw in there plus the set screw Joe showed you just to keep it tight. I don't have any photos of one but most the time I use a 22 rifle shell that I drill out and have the set screw running through it. That way I just have to run my hex head wrench into the shell case when the engine is running and the screw head is easy to locate and the wrench doesn't pop out due to vibration when I'm adjusting the high end. You could probably use a 2-56 screw but I had a lot of 4-40s in my box over the years and used that size. It's clean looking and works well. Just another way of doing things. A bit more work though.