Friend has a Troy Bilt walk-behind Mower with a 6.75 Briggs Engine. The only way he could start it was using starting fluid. He took it to a Mower notable shop and they said the Carburetor is bad. They put on a new OEM carburetor. He got it back Home and it wouldn't start any better.  He took it back and they said the Engine compression was low so it needs a short-block.  They didn't offer any compensation for the previous repair.  Before tossing it, he asked me to take a look and I found Auto-choke was holding the butterfly wide open when Engine cold.  Removed the Engine shroud and discovered the plastic Vane for the Auto-Choke was warped causing it to hit the underside of the Shroud.  I heated it up with a Torch and lowered it a bit.  Put the shroud on and it moved freely.  Now the Mower starts on the first pull.  It seemed simple to me as I fixed it while he waited.  I'm assuming the Repair Shop tested the Mower with the Shroud off?