compression vs valve adjustment
 

when i first recieved this 1977 911 2.7 , the first thing i did was a compression test, well all the cylinders were between 150 and 120 number 3 was the highest, well the car wasnt running to good so i then did a valve adjustment and it still was running bad , well me and a friend just did another compression test and now number 3 has 60 pounds , could the valve adjustment cause me to lose that much compression?

If it was done incorrectly it could. Valves that are set without enough clearance will be damaged.