How do I adjust the valves on a Briggs and Stratton Intek V Twin

SOURCE: Stratton Briggs Stratton Intek V - Twin Engine 21

The oil is contaminated with water. Change oil and filter, if it has one.

SOURCE: briggs and stratton miss fires on one cylinder.22hp intek

possibly a commpression test might throw a little more light on the situation ,that will eliminate alot of speculation, and make it easier

SOURCE: Briggs & Stratton Briggs Stratton Intek V -

these are common for doing this ,if you dont want to pull it down and hone the cyl. then i would use a heavier oil say 20w/50and that will probabley solve your problem

SOURCE: Can a novice replace a carburetor on a Briggs

Yes its pretty easy you can do it.Are you sure the carb is bad most of them just need a good cleaning .I would disassemble be careful there are some little parts in there and if you are careful and pay attention as you disassemble it you can just clean it .Go to auto parts store get a can of spray carb cleaner .remove bowl be careful the is a float in there a little square or round bellows .Slide the pin out and then the fuel loat pin underneate the float now take out any adjustment screws you can find and spray cleaner in every hole you can find several times and reassemble if idle or fuel mixture screws were removed a standard setting of 1 1/2 turns out from seated position is the norm and some adjustment may be needed once running either in or out till runs smooth.

SOURCE: Briggs and Stratton Intek V

Misfiring could be caused by simple things like fouled or worn out sparkplugs or an ignition system that is slightly faulty or Fuel problems such as dirty or stale fuel or clogged filter causing a leam mixture. Some B & S motors have an switch that cuts the Ignition if the oil pressure or oil level is low.
Another cause could be the Valve clearances are out of adjustment.
Armed with your Engine Number, visit the B & S Website for comprehensive information and specifications as well as a good FAQ listing.