Anyone know Briggs&Stratton motors?

Ok if someone can help i would appreciate it.I have an 18H.P. lawn tractor with a Briggs&Stratton motor it will work fine for the longest time then all of the sudden it will start missing like hell and blow large amounts of white smoke out the exhaust.I then disengage the mower and idle it down and it clears up,then maybe another 20-30 minutes later it will do it again.I called there hotline what a joke that turned into all prerecorded crap,i was on for 20 minutes and never did talk to an actual person :x Also tryed Sears where i bought it and the same thing.Why can't they have atleast one live person to talk to :?: Any help would be appreciated.

I quit working on lawnmower engines about 8 years ago. But I would check the exhaust valve clearence, it might be a little to tight. Clearences used to be .010" on intake valve and .012" on exhaust valve, when cold. Check your owners manual to be sure that they didn't change the clearences in the last few years. If there isn't enough clearence , it will start to stay open when it gets good and hot. Also take a look at the spark plug, if it is white or has white build up, you may have some carbon buid up getting broken loose and getting onto the valve seat. If it is a champion spark plug ,Throw it out!! try these things and let me know what happens?? I hate when you call someplace and get the automated phone system, GIVE ME A PERSON TO TALK TO!!! :x

Thanks for the info. i'll check these things.

You might have water in the gas also,especially if iy sets outside like mine.

large amounts of white smoke? my push mower does that if it gets flooded then starts up. i let it idle for a minute, then it clears up and i go up on the throttle... maybe its just not breathing enough (filter) when it starts lugging?