My B&S 6.0 won't start.. It will try to run but sounds like "only 6 of 8 are firing" then it stalls. I've cleaned all filters, and carb.

If you cleaned the carb then look for fuel delivery issues.

Older Briggs have a low and high speed idle screw, so be careful of that.

Make sure the gas gap is vented and if there is a solenoid on the carb, that will prevent fuel from flowing too.

Without specific model #'s it really difficult.