Don`t these isv valves have like a rubber diaphram inside.
I did wonder if that nut locking the stub was like an adjustment thing for say throw of the diaphram.
Bit like the adjuster on a fish tank air pump.
Car horns used to have a simular thing for controling the oscillation of the vibrating disc so hence alter the tone.
Somebody may have pulled an old one in bits so may know.
Be nice to know just incase i`m talking out my rear lol.
Fred.
