Tuning the 75-B carbs

[rickthefix]

I've tuned quite a few carbs over the decades, so not a newb, but these are different than the 77 to 81 XS carbs I've worked on.
I'm guessing here at the moment, so corrections please if needed and maybe actual correct steps.
Sync'ing is easy, have my baby bottles set-up for that. It's the other stuff I need info on
I'm seeing "air" screws on the sides right by the intake boots.
Then there's the brass plugs underneath that have probably not been removed before? Assuming this is the factory air screw there.
Thinking I'll leave the brass plugs in since it seems to run pretty well.
That leaves the air screws on the sides.
Warn up to normal op temp, turn off the fuel to the right carb and let it run out of fuel.
Run the idle up to 2k on the one running carb.
Adjust the air screw until it runs the idle up to highest point then back off the screw 1/8 turn or so.
Then do the right side.
Then sync them.
Does this sound about right?

 

[5twins]

I'm not sure what that brass plug on the bottom of the carb covers, but I can tell you it isn't any sort of adjustment screw, so yes, leave it there. There is only the one mixture screw on the side of each carb, and notice I called it a "mixture" screw. It's not an "air" screw even though many of the manuals call it that. It is a true mixture screw, regulating roughly 25% of the fuel/air mix flow from the pilot jet into the idle circuit. Turning it out makes things richer, in leans it out. And I'm not sure what those blue things are above each throttle shaft, maybe added vacuum nipples so sync gauges can be attached? If so then that's a better way to sync the carbs.

 

[rickthefix]

I'm not sure what that brass plug on the bottom of the carb covers, but I can tell you it isn't any sort of adjustment screw, so yes, leave it there. There is only the one mixture screw on the side of each carb, and notice I called it a "mixture" screw. It's not an "air" screw even though many of the manuals call it that. It is a true mixture screw, regulating roughly 25% of the fuel/air mix flow from the pilot jet into the idle circuit. Turning it out makes things richer, in leans it out. And I'm not sure what those blue things are above each throttle shaft, maybe added vacuum nipples so sync gauges can be attached? If so then that's a better way to sync the carbs.

Yes, home-made vacuum port screws with blue caps. I made those long ago. Thanks for the info, I'll sleep better tonight

 

[5twins]

As far as setting the mix screws goes, I don't use the dead cylinder method, never needed to. On the BS38 carb sets, I've always been able to hear the difference in the way the cylinder runs. Go a little too far past the ideal setting or "sweet spot" in either direction and the cylinder falters and slows down or runs rougher. It sometimes helps to slow the idle speed down a little, to around 1000 RPMs.