Boy, those plugs are burning very clean, maybe too clean, lol. One of the first rules of jetting for mods is that when you think you're right, try the size above and below where you're at to verify. Obviously you know a size smaller is no good, but another size up could be even better than where you are now. The nice thing about these BS38s is that you can swap main jets right through the drain plugs with the carbs still in place using a stubby screwdriver. I've even done it on the side of the road while jet testing.
Yes, the '76-'77 carb set is said to be one of the best of the 38s. It was the first to have a linkage, which makes syncing easier, and was old enough to not be too E.P.A. mandated. Because of this, I wanted to try them and acquired a set for my '78. I have the basic "pods and pipes" mods (UNI pods and the older, good Commando mufflers) and the final jetting I arrived at was one up on the pilots (to a 27.5), four up on the mains (to a 132.5), and the needles leaned a step to slot #2. 132.5 mains were the largest I could fit without incurring upper midrange break-up even with the needles leaned a step.
There are various jetting recommendations for the 650 around the internet. MikesXS used to have some, calling for mains up into the low 140s. That can work for some of the other 650 carb sets that came with larger mains to begin with, but you'll never get mains that big to work in this '76-'77 set. It's just too many sizes up plus the very large (rich) Z-8 needle jets won't allow it. So, re-jetting these 650 carbs for mods is more about the number of sizes up than the actual sizes themselves. Usually one or two sizes above stock is all that's needed. I run 140 mains in my '78 carb set but that's only two sizes above the stock 135s. These '76-'77 carbs can often use more sizes up because their stock 122.5 was so small.
