Did you by chance leave out the balance pin during assembly of the primary chamber and diaphragm?
Another thing I have seen happen is installing the balance pin diaphragm upside down which will cause the balance diaphragm to rupture and let unregulated LPG to be sent out of the regulator fuel delivery hose to the injectors.
The balance diaphragm and pin help to fine tune the regulator to compensate for a range of pressure differences in fuel tanks due mainly to ambient temperature changes.
Are you getting the O-ring installed properly (that seals the primary valve brass pivot base to the aluminum regulator body)?
If that O-ring is missing or installed incorrectly, unregulated LPG will the result because LPG is bypassing the primary valve.