I have a sears 5.5 horse lawn mower. One day it didn’t start and a neighbor came to help. He tried to adjust the carburetor (messed with the 2 screws) and now it won’t start or when it does it stalls out. Is there a way to set the screws so it is a right mixture. Also somebody told me that this Tecumseh carburetor is a fixed one that the screws only adjust the throttle and the butterfly. Is this true. I would appreciate any advice you can give   Thank You Ralph