demon carb underated to begin with its more like an 850

 

no one mentioned it but if when you floor it the car stumbles really bad and then goes it could be either ignition relation or the (I think it's called) "accelerator pump" in the carbuertor can be bad, it's a little rubber diaphragm that can tear. (been away from carbs for many years)

 

true ! the bog could be from it not working at all ,or flooding it ( blackish smoke)