23 hp briggs vanguard Model: 380777 Type: 0142-E Code: 01012311 on a simplicity ZTR, engine replaced Belongs to a friend I'm trying to helpout... Last year we replaced a coil that was misfiring about half the time and it ran great till now. The other day it started acting up, popping and sputtering and black smoke running rich. Changed the plugs, and it ran smooth as long as it was sitting still, seemed like it was flooding when we tried to mow with it. But then started misfiring again. Removed and checked the new plugs and they were firing through the side of the porcelain. Changed the plugs and removed the kill harness from both coils. The diodes ohm out alright, but is it possible they're not working at times, and the rapid/double firing is ruining the plugs? It runs fair with the air filter removed, but turns rich with it installed. The filter was new last year, and looks good. I know about the 2 different air filters for the briggs and the kohler, already been through that. Also, there are 2 vent tubes on the carb, are these supposed to be open, or connected to something or plugged or what? One was plugged and one was open, but when I removed the plug it ran better, ie stopped flooding. Been through the carb and it's CLEAN! Is it possible to generate enough centrifical force on the carb when turning to cause fuel issues? It seems to sputter quite a bit when spinning hard. The air intake is to the back of the mower, and the whole engine sits behind the drive wheels. But it did run great last year... Anybody got any other ideas? Is this particular carb a "bad" one? A local shop said they changed them mid year. Would bad diodes fry the plugs in 30 minutes like an old 2 stroke? Thanks for your help.