Small Engines (Lawn Mowers, etc.): have to leave in choke to keep mower running., briggs surging, run with choke on

Question
i have a myrray 2004 16 hp 46 in cut, model # 402707 b&s twin I/C.  i have to leave the choke on to keep it running.there is some smoke not too much,after i cut for about 30 min it wants to cut off.i have to keep adjusting choke, pulling it in and out to keep it on.plugs have been changed and oil as well,and filter. is there anything that i am missing.

Answer
The carburetor probably needs rebuilding.  There's probably a fuel pump on the front of the carb that will need rebuilding as well.  This is a very common problem, especially this time of year when engines are coming out of storage.  Choking the engine does two things, it limits tha amount of air allowed into the fuel-air mix and raises the speed of the air through the venturi which pulls a little extra fuel out of the bowl.  So by cleaning thoroughly, in a soak can, spray cleaner isn't very effective for this sort of thing, you remove the deposits that are clogging things up.  Let me know if you have any questions.  Thanks, PK.