I had an issue a couple of years ago with these breathers - I spoke to others who were still using the CV carbs without the airbox and learned that these breather could be
open to the air without the need to have the negative pressure from the airbox - This suited me as one of the tits had broken out of my airbox so I sealed the
airbox openings and put a bit of gauze in the breathers to prevent anything crawling in and off I went -
These breathers (pay no attention to the broken fuel line)
Anyhow - the bike wouldn't rev out over 6 to 6.5k revs - took me a few days to realise that it was the breathers without the airbox negative pressure that was the cause.
I had another airbox in stock, fitted it, reconnected the breathers and end of problem.
The reason I bring this up now is because when searching for a fault in the last week, on re-installing the carbs, I neglected to connect one of these breathers to the airbox
with the same result as before - I instantly knew what the problem was this time tho.
I am guessing that this negative pressure assists in keeping the bowls full to the correct level with fuel - when I gas the big girl she must take a healthy slurp of fuel.
My setup is as follows -
BS36 (XJR1200)
Main 165
Needle 5D66 (3rd from top)
Pilot 45
Pilot air 135
The BS36's have a Throttle Position Sensor which with the IgniTech ignition I am using allows me to vary the ignition timing with reference to revs and throttle opening.
I intend returning to the dyno and tweaking these values with a view to finding some more HP/Torque
at the moment ...... BTW - she has 1170cc and the camshafts are actually 1978 XS1100 cams (not Tighe cams - that's another story) dialled to 110 lobe centres.
That August 2012 curve was when the machine was still a shaft drive.
