Small Engines (Lawn Mowers, etc.): Craftsman Push Mower, craftsman model, push mower

Question
6.5hp B&S craftsman model # 917-388521 Hopefully this is something easy. The mower has recently started to rev high at start up and then mow fine but the mower will not start when the engine is warm. Will start after being left over night.

Answer
Try replacing the spark plug first.  Is the air filter clean?  I suspect some debris in the carb causing the surging.

Here is your engine model number: model 123k02, type 0258


Briggs carbs will run a little longer than Tecumseh carb if ther is some debri in the bowl.  Do you have an air compressor and any experience cleaning carbs?

Here is a picture of you carburetors inside:

http://www.lawn-mower-shop.com/carb2.htm

Below is a site on carb cleaning.  Although it is for Tecumseh carbs, the process is the same for Briggs carbs.

Let me know if this helps.

Eric