carb question - t9.9ELHP

[Incantation]

Can someone tell me what this assembly is? It sits on top of my carb on my Yamaha T9.9ELHP and when the motor warms up the pin moves down and the motor chokes.. if I pull it up i'm able to raise the rpm to a stable level and the motor functions normally. I opened it up and the assembly looks fine but I'm no expert and it's clearly not functioning properly; any advice would be appreciated. I'm sure if I take it to the dealer they will tell me I need an entire new assembly $$$

The first image is with the housing on





Thanks,
Inc

[boats.net]

It's the auto choke. It has to be perfectly clean inside, may need new diaphrams and plunger. If that doesn't resolve it then would need new carb.