There could be several reasons why your 1973 Harley Ironhead has consistently started and run well. Here are a few possibilities:
Maintenance: Regular and proper maintenance is essential for the smooth operation of any vehicle, including motorcycles. If you have taken good care of your Ironhead by performing regular tune-ups, oil changes, and other necessary maintenance tasks, it's likely that the motorcycle is running well as a result.
Reliability of Older Technology: While the technology in your 1973 Harley Ironhead may be considered older or more basic compared to modern motorcycles, it doesn't necessarily mean it's inferior or unreliable. Motorcycles from that era were often built with robust components and simpler mechanical systems, which can contribute to their reliability and ease of maintenance.
Personal Care and Attention: As an owner, you may have developed a deep understanding of your motorcycle over time. By being attentive to its needs, making adjustments, and addressing any issues promptly, you could have contributed to its consistent performance.
Regarding the hose from the breather to the final drive chain, it's not a standard or factory-installed feature. It seems you have made a modification to your motorcycle, and without further context, it's challenging to determine the specific reason behind it. However, some riders might choose to direct the breather hose towards the final drive chain area to provide additional lubrication to the chain or to prevent oil buildup in certain areas. It's important to note that modifications should be done with caution and consideration for the overall functionality and safety of the motorcycle, as they can impact performance and reliability. If you have concerns or questions about specific modifications, it's best to consult with a knowledgeable mechanic or Harley-Davidson specialist.