RE: Mikuni HSR42 vs HSR45
I reviewed your dyno chart and believe your torque curve is a function of the exhaust. Too few dics in the mufflers will produce this curve and adding more would be a way to test. As we add discs we may start do develope a dip around 2700 rpm, which is not always wanted on a touring bike. Also, some true dual head pipe systems can contribute to a drop off of hp above 4k rpm due to their lenght and lack of staging. We do not normally make exh changes as part of dyno tuning unless instructed to do so by the owners. This adds to dyno time and therefore cost to the customer and the setup on exhaust, as we recieve them, is often what the owner has established through their own riding impressions and does not want changed. Last, changing discs in an older high milage system can be problematic in that screws break off and threads in the baffle gaul or strip out.
As an exhaust issue, adding more carb will not help. The 42 should be ideal for your application and can support up to 100hp. Up to 90hp the Force or Hyper-Pro would be OK. The standard Hypercharger is too restrictive and both become restrictive above 100hp.
I would like to see your bike back on the dyno to investigate this issue. If you are up for it, we can work something out with our service manager to make sure your bike is as good as it can be for your riding style and the investment in perfomance upgrades.
Please let us know if you would like us to revisit the tuning or discuss options, we would be happy to do so!