[redmodelt]

In the distance past, there was an issue with where the needle passed thru the clamping area and the fix was to remove the little ring at the bottom. If your ring is missing replace the needle valve as suggested above. That little ring helps keeps pressure from the fingers on the needle so it stays where it is set at. The rubber grommet helps but is more for anti-vibration. Also, clocking the knob so the little projection is at the bottom when in running position. Few people realize that is a tiny counter weight, same with the knob on the junction box cover nut, made so if comes loose, tends to point down and not vibrate around and off.