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According to where I purchased it's never been touched, what makes them tamper proof?
If you will notice, your carb has tapered "pilots" on the end of the mixture screws. This was used to facilitate the installation of "tamper resistant" plastic caps on later model carburetors. I worked for an Olds dealer in the early '70s and we would pop the caps off when a customer complained of a rough idle, adjust the carb, then put them back on. Below are pics of a 7040253 that I sold some time back and a 7040250 that Sparky rebuilt for one of my customers, which have the older flat tip on the screws.