Small Engines (Lawn Mowers, etc.): I have 4.0 hp Briggs engine..., hp briggs, lawnmower

Question
I have 4.0 hp Briggs engine on a lawnmower. this machine is about 1 year old and it worked just fine until one day it was running o.k. and then it choked down and blew out black smoke with the result of no power. I have changed filter, plug and cleaned carb. This is a throttle free engine and it is about as simple as it can get but cannot find trouble. When starting engine it runs o.k. for about 3 seconds and then choks down.

Answer
If you are saying that it runs so rich (black smoke) that it quits, the high speed mixture screw, if equipped, may need to be adjusted.  Start at 1 1/2 turns out from lightly seated.  Then turn the screw in until the engine starts to surge.  From there, open the screw 1/8 of a turn.  Otherwise, you will need to verify the float level and that the needle, seat, float and pivot are in good working order.  Hope this helps.