Tractor Repair: 22hp Briggs power issues, air fuel mixture, briggs and stratton

Question
Hi, i have a Craftsman 22hp briggs and stratton lawn tractor. When ever you rev it up all the way or Put the forward pedal down for max speed or put the tractor under little load when snow blowing it loses power and blows black smoke. the carb is clean , new plugs and changed the air filter.. Please help... Is this a vaccume issue??

Answer
Hello,

  I don't normally work on lawn and garden equipment, but I've been a mechanic long enough to tell you that it is definitely not a vacuum issue.  Anytime you see black smoke it means the air / fuel mixture is too rich and it's getting too much gas.  If you had a vacuum leak it would be too lean and not getting enough gas for the amount of air being drawn in.  Have you tried adjusting the mixture screws? If you've already replaced the air filter, the next thing to check would be the carburetor.  Even though you say the carb is clean, that doesn't mean it couldn't still have a problem.  Check to make sure the choke is opening all the way first.  Sometimes the cable can  slip in the clamp and it can get out of adjustment.  The float could be sticking, or the needle valve could be leaking.  If it has a diaphragm  carburetor, then I don't know.  I'm not familiar with those.  If the choke is OK and it has a new air filter, we know it is getting enough air, so then it would have to be getting too much gas which leads us to the carburetor.  Also make sure it has good fresh gas in the tank.  Bad fuel can cause a similar problem.

                      Arnie