Topic: Quite possibly the dumbest question ever asked.

[robdrobd]

Let me preface this question by saying that I have never tried to fix a motorcycle. That being said, where do all of the gas lines connect to that come from the carbs on a 1975 cb550f? I know two of them go to the petcock, and I know that the set of four overflow ones connect to the bottom of the bowl. But where do the other pair attach that originate in the center of the rack?

[Gordon]

The two hoses that aren't either fuel lines from the petcock or overflow lines from the bottom of the bowls are vents.  They should be routed up and over the air box and back down to where the overflow lines go. 

[wdhewson]

These other two lines might be air vents.  

Since carbs operate on venturi induced suction, the atmospheric pressure above the fuel in the bowl should be the same as outside the carb.  I usually route these lines with the open ends down so debris and water are less likely to enter.

What do others think?

[robdrobd]

Two of the lines are smaller and are more toward the center of the rack. Two are a little larger and are more toward the outside of the rack.

[Frostyboy]

The two hoses that aren't either fuel lines from the petcock or overflow lines from the bottom of the bowls are vents.  They should be routed up and over the air box and back down to where the overflow lines go. 

+1
I consider a dumb question as being one that was never asked.
I have my rack apart at the moment & this is the correct answer. 1 & 2 are joined by a short 3.5 tube as are 3 & 4. These 2 that you speak of emerge between both pairs of carbs & vented to the atmosphere.

[SohRon]

Sorry I don't have a better pic, but I think you'rre refering to the two hoses shown here. They run to two vents located between no.2 & no.3 carbs. All of the carb vents/overflow drains use the same 3.5mm hose; you can get it from Bike bandit in a 3000mm roll. Hope this helps.

[robdrobd]

Sorry I don't have a better pic, but I think you'rre refering to the two hoses shown here. They run to two vents located between no.2 & no.3 carbs. All of the carb vents/overflow drains use the same 3.5mm hose; you can get it from Bike bandit in a 3000mm roll. Hope this helps.

Those are the ones. So they are just vent hoses that should end right next to the bowl vent hoses?

[SohRon]

These vent hoses attach to the bowl overflow tubes with clips, routing down from the carbs between the engine and swingarm. These two particular hoses don't actually reach the bale that hold the O.F. tubes, at least in the applications I've seen; they actually stop a few inches short of the bale, or just below the swingarm.

The white clip actually belongs above the black clip; see above pic, lower left corner, where you can see the clip located correctly.

One thing... this is a "K" frame. I don't know how different things are for the "F"s; I believe they have an extra couple of vent hoses on each end as described above. At least this will get you into the ballpark with these particular hoses.

[Frostyboy]

If nothing else SohRon, your pics have convinced me not to post too many close-ups of my bike. It's beautifully presented man. 

[robdrobd]

Man those are some nice looking carbs.

[SohRon]

Well, thanks. I hope this helps you get your problem straightened away. 

[gregimotis]

Well, thanks. I hope this helps you get your problem straightened away. 

It helps me to be jealous of your rack... err um, yeah.