For the typical "pods and pipes" mod many of these bikes get, the usual re-jetting scenario is one or two up on the pilots, one to three up on the mains, and the needles leaned a step to compensate for the larger mains. But the '76-'77 set is a little different than the other BS38 carb sets due to the very small mains it had stock (122.5). It may need a little more on the mains, like 4 or 5 sizes up. If you study this jetting chart I drew up, you can see how main jet size is related to needle jet size. Larger needle jets get smaller mains and smaller needle jets can use larger mains. The Z-8 needle jets used in the '76-'77 set are the largest ones put in any 650 carb set, and they get paired with the smallest mains ever used .....
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Now, you may have read jetting recommendations on the web (MikesXS, Minton Mods) calling for mains in the 140's. That may work on some of the other carb sets that had smaller needle jets and bigger mains to begin with, but you'll never be able to go that big on a '76-'77 set due to that large Z-8 needle jet it has. As I mentioned earlier, 132.5's were the biggest I could fit, but that's 4 sizes above stock. Keep in mind, when re-jetting it's not so much the size of the jet that matters but rather how many sizes above stock it is. By comparison, on my '78 with the '78-'79 carb set, I run 140 mains. This does align with the common recommendations but it's only possible to go that big because of the small Z-2 needle jets, and it's only 2 sizes above the stock 135's.
When you're close on your jetting, one size can make a big difference, so it's best not to skip around or skip sizes. Try every size in succession. Yes, when it's all said and done, you're going to end up with extra jets but it's just the cost of doing business, lol. $40 in jets is still way cheaper than taking it to a shop. They would charge you several hundred dollars I'm sure.
Now let me talk about pilots a little bit. I'm one size up on my '78. I'm playing around with an XS500 carb set adapted for 650 use on my '83 at the moment. It's jetted based on a '76-'77 650 set (Z-8 needle jets, 4M1 needles). I had tried another '76-'77 set on my '78 several years ago so based my jetting on that, in particular the one size larger pilot. Well, on the '83, this wasn't enough, I had to go up another size. I had lots of popping on decel I couldn't tune out with the mix screws. Then I remembered - years ago when I was first tuning the carbs on my '78, I was up 2 sizes on the pilots. Then I rebuilt the topend and ported it. This porting changed the flow and I was able to reduce the pilots a size to just one over stock. The '83 isn't ported so I guess that explains why it needs 2 up on the pilots.