I do not remember the formula

Everything is working but I have one problem. When the psi in the tank reaches 80 psi, the gas motor shuts off.
It does not roll to a stop. It stops on a dime.

The engine is a 5hp Briggs and Stratton. I runs very well normally or when uncoupled from the compressor. I have the check valve/ unloader installed. But I do not have the throttle from the unloader to the engine

I imagine you all know more than me. I really do not think the throttle cable not being installed yet, would cause this. Any ideas would be appreciated