Question: when did yamaha start making 4 stroke outboard motors
[{'answer': '1984', 'provenance': [{'wikipedia_id': '39846', 'title': 'Outboard motor', 'start_paragraph_id': 24, 'start_character': 494, 'end_paragraph_id': 24, 'end_character': 498, 'bleu_score': 1.0, 'section': 'Section::::History and developments.:Four stroke outboards.\n'}]}, {'provenance': [{'wikipedia_id': '39846', 'title': 'Outboard motor', 'start_paragraph_id': 24, 'start_character': 0, 'end_paragraph_id': 24, 'end_character': 1283, 'bleu_score': 0.9193829979672851, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15304793810588661400}, 'section': 'Section::::History and developments.:Four stroke outboards.\n'}]}]