screws on butterfly in carb keep coming loose

[daddy3]

troy bilt 42" 18hp with fuel stop on bottom of bowl ,these two stupid screws on the main butterfly keep coming loose i have put locktite on them ,tryed indenting the back side of screw ,and tryed new screws, mower has 500 hours it and the rod that the butterfly bolts to is slighty slighty loose at the bottom do u think maybe there could be a little vibration causing this! choke butterfly is in the front and pushes in a slot in the front rod

 

[jeff]

Sounds like The threads in the shaft may be damaged. Get a new shaft and use the locktight when you put the screws back in