Yes, that's what I meant...the carb boot holders on the intake, have the barbs for the vacuum lines that originally went to your petcocks...to essentially "pull" fuel when the bike is running.
It looks the the PO on your bike isn't using the other petcock, and has capped off the barb. This isn't a problem, as many people get fed up with the vacuum petcocks and just use one. (Your carbs are connected with a fuel line in between them so it's ok to just use one petcock to feed both carbs).
Yep, so on the one side with the line still connected, if you pull that when your bike is running, then it should want to stall out... and same with the other side, but instead of a line, it will be a little "cap"...pulling that off should likewise want to make the bike stall out.
If when you do that on either side, if the bike runs the same or even increases in RPM, then you're running rich on that side.
The Dead-Cylinder method is a little hard to grasp without actually doing it...but essentially, you want to get each cylinder to be hitting about the same RPM. And to find that out, you need to isolate each cylinder...in practical terms, you want to have the bike running only on one cylinder at a time so you can measure the RPM of the cylinder that is firing.
The way I do it (note: I'm not an expert, but this works for me) is assuming the carbs have been cleaned, and are bench synced, I then make sure both carbs are synced using a manometer while running. Oh, also get a big fan to keep the bike cool as it's going to be running for a bit of time and you want to avoid overheating.
I then set both air/fuel mix screws to their factory settings (2 1/4 turns out I think for the '79 BS38's). Then start the bike and I get the idle to hover to the lowest setting before it will die if I ground out one plug...for me this is around 1500-1800 RPM. (Although I've had to have it up to 2000 before when I was first trying as I was a little unsure of what I was doing)
So now it's idling high, and it's time to address the air/mix screws...so let's say I'm working on the right cylinder first: (So I want to stall out the left cylinder)...
(Oh another note: With a "points" ignition, you want to ensure that plug wire is always going to spark... so don't just unplug a wire from the spark plug when running. It's bad for the coils...if anything you can put another spark plug in the wire (leaving the one that's on the bike where it is) but it's hard to do when the bike is running...lol.)
Pre-work:With the bike not started, I keep both plugs in their sockets...I pull the cap off one side, and connect a jumper wire from the tip of the plug to the connector inside the plug wire and have a large screwdriver handy...
Now...back to where I left off: start the bike up, it's idling high and I simply touch the screwdriver to the cylinder fins, and the tip of the exposed spark plug (with the jumper wire on it)...this will stall that cylinder.
What you should hear is the one cylinder cut out, and the idle will come down as it's solely working off of the right cylinder only... now go to the air/fuel mix screw and turn it to the right... speeds up/slows down the rpms? Then go back to the 2 1/4 turns and now go left...speeds up/slows down the rpms? You're looking for the speed that's the highest rpm that's steady and smooth... (Generally try leaning towards the richer side of things)...I try to get the RPM's to be at about 1000rpms on that side and running the smoothest/best.
Turn bike off, connect the left plug back up and switch jumper wire to the right side, and do the process over for the left cylinder now...
Once you've got them both set, adjust the idle speed to 1200rpm, and you should be good to go. You may want to do a little ride and then come back to check your spark plugs, and see how they are burning.
Hope that helps, and I'm sure others will jump in with better details on the dead-cylinder method... or things that I may have missed.
