Small Engines (Lawn Mowers, etc.): 17.5 Briggs Stanley Riding, slow reply, fuel outlet

Question
I have a 17.5hp Stanley riding lawn mower (Murray). when I first start it, the idle speeds up then idles down. I will keep doing this until I start mowing then run fine. But after I have been mowing for about 30 mins. it will shut off and i can start it up and mow for 5 mins and it will do it again. I checked the carb and it looks clean, no water in gas, could use anew air filter but don't think that could be the problem. Does riding lawn mowers have a safty thing where when the gear oil in the hydro gear gets low it will shut off? the oil in the motor looks good but when i first ride it it sounds like the gears are working extra hard for the first few seconds in the hydro. Not sure what in the world it could be. Plese help me with this crazy thing. If you need any info on the lawn mower please ask.

Answer
No safety "gizmos in the transmission.  Sounds like a coil to me.  When it dies and won't restart immediately check for spark.  If no spark, you need a coil. If you have spark you have a clogged fuel pickup in the tank, or, a chunk of crap sucking against the fuel outlet.

Sorry about the slow reply.  Fathers day, what a pain in the ass!