I am a novice mechanic. My 12.5 b&s (Murray) was leaking fuel from the carb. I put in overhaul kit for Nikki carb. Solved fuel leak. Now mower only runs when holding in clutch. Engine stalls when release clutch to engage drive belt. Thanks for your input.

Check your safety switches.

THANK YOU MOWERMAN2468! You were absolutely right. :) The kill-switch under the seat had fallen down into the mower housing. Now if I could only adjust the carb. Again, it is a B&S 12.5 hp, the numbers are: 28V707 1113-E1 010131ZD with a Nikki carb. Thanks.