85 cb700sc Nighthawk carburator air tubes

[SoCalMotoClassics]

Greetings fellow rider's . . .an update on my 85 cb700 Nighthawk . . . Thanks to Shinyribs recommendation, I went with a new set of Shinkos, and Tools help put me on the right track with my clutch issues, new brakes, fluids,  corrosion control, lube, oil and cleaned the carbs.  Some idiot used silicone sealer on the bowls.  Had goo stuck to everything.  The bike had California smog, so there were multiple vac ports were capped, but two hoses in between carbs 1&2 and 3&4 had some L Shaped open lines connected to what the service manual refers to as "air tubes".  I assumed it was more Cali smog crap, decided to plug them so the carbs wouldn't suck crap through the open tubes.

After assembling bike, would only run with choke full on, suspected fuel issue, but had replaced fuel line and filter, tank is very clean with fresh gas.  Decided that since it ran with open tubes it could be the caps I put on the air tubes, took them off and the bike started right up on first crank with new NGK iridium plugs (thanks to the forum tip).

Big question, what's the function of the air tubes? And, if they need to run open, should there be some form of filtration?  Perhaps it was part of fuel vapor recovery?  Anyway, the bike runs and rides so much better. The Shinkos ride just fine and I was able to get them mounted and balanced for 47 bucks.  

Thanks in advance

[TOOLS1]

I assume they were the carb bowl vents. You could put a fuel filter on the open end of them, but most bowl vents just hange down open.
TOOLS

[SoCalMotoClassics]

The service manual made little reference to them, but did see an exploded view of engine assembly showing hoses on the air tubes dressed back towards air box connected to nothing.  I'll just do the same and call it done.  Thanks for the support.  Now for some cosmetics . . .

[SoCalMotoClassics]

Hello, I'm seeking some guidance on a pesky carb issue. . . I changed my aging fuel lines, went with clear fuel tubing for the time being to monitor fuel/tank debris as I continue tinkering with bike.  After it had a week, the line and filter after the petcock were visbly empty, with no fuel remaining.  Decided to check oil, had a very noticeable gas smell. Last time I rode, it went through a tank in short order.   I suspect float needle valve(s) not sealing, allowing fuel to leak into cilinder(s) and weep down into the oil.  This is probably the cause of poor idle as well.  Any tips are appreciated that can help me troubleshoot this further  before I tear out the carbs again.  Thanks in avance for your response.

[TOOLS1]

Two things here. One, your petcock is not shutting off and allowing gas to flow to the carbs. This would not be a problem if not for number two. Number two, one or more float needle valves are not sealing. Either the needle valves are worn out, or the seats are dirty (clean them with a Q-tip and chrome polish), or your floats need adjusted, or even replaced.
TOOLS

[SoCalMotoClassics]

Thanks for the sound guidance Mr. Tools1.  Had tank off for a week with gas in it, never leaked.  Petcock does weep in the on position, but is gas tight in the off and reserve position, so I've been running in reserve for now, but now is a good time to deal with both.  There's a kit out there to rebuild the sealed petcock by drilling out the rivets.  The kit I ordered on Amazon for petcock only came with diaphragm parts. I'll change the oil and filter once the fuel problems are fixed, go with Rotella T.  I did install new needles, rubbers looked good, but did not service seats.  I'll be sure to do that and more this time.   Thanks again for the prompt response.