Depending on what the pipes are you may need to reject, however I think this strange sound and loss of power could be anything from ignition to carbeuration. Spark plug wires should not be taped so thats a weird item. I am not sure this is the best shop since their answers and actions sound unprofessional. You should not have to clean carbs if you used a fuel conditioner such as Stabil. Otherwise they may be a bit gummed.