Topic: What is This Hose for and Were Does it Go - '75, CB750F

[RSchaefer]

I'm putting this thing back together and am attempting to put it back together as it came from the factory.

Look at this picture and you will see a fairly large black rubber hose coming up from below and connecting to a built-in clamp on the front of the battery box.





Its rusty in the photo but there is a flared metal tube, maybe 1/2" long shoved into the top of that tube on the battery rack.

At 1st I thought it was from the oil/crankcase filter mounted at the bottom of the battery rack, but its not really showing up in that drawing and I have the oil filter unit mounted and all of the hoses accounted for?

Then I thought maybe its a vent from the gas tank, but again the gas tank vent drops out the bottom of the bike.  And nowhere can I find that hose in the parts list or the associated flared metal tube insert?

It does not appear to be the battery overflow and does not fit on my batteries overflow connection in any case?

The bike came from the factory this way and was not part of a PO mod!

Anybody have an idea what it is?

[goldarrow]

 battery acid overflow drain hose

[seanbarney41]

+1...I don't what the flared metal thing is doing in there

[RSchaefer]

Well maybe, but?

Here are the pictures:



20" long



Funny thing is the last 5" at the bottom is slightly smaller in OD then the rest of the hose AND that last 5" is solid, does not flex?





Solid, can't flex it?



Here is the typical battery vent tube



Here is the flared metal tube insert







Maybe the smaller vent tube gets shoved into the larger black tube with the metal insert?  That said, my manual shows the battery vent tube going through the oval bracket on the back of the engine along with the carburetor vents tubes, BUT the bottom OD of the black rubber hoes does NOT fit in that oval bracket?

[Powderman]

Breather tube off the back of the valve cover.

#8
http://www.cmsnl.com/honda-cb750f-750-super-sport-f0-1975-usa_model493/partslist/E++01.html#results

[goldarrow]

Looks can be so deceiving sometimes lol

[RSchaefer]

Its not the breather tube off of the valve cover.  Looks like it must be for the battery vent tube, I just never had seen it done this way and did not know that hose was there to capture the vent hose from the battery and it appears to be contrary to the diagram in the small owners manual that has the battery vent tube going through the same oval at the back of the engine for the carburetor vent tubes.



In the diagram I circled the clamp that's on the front of the battery box.  Item #7 is described as the "Tube Assembly, Battery" so its an "assembly," you can kinda see in the picture there is something in the top end of that tube assembly.

[Kickstart]

Yes, going off of recollection, which is dangerous for me ....

I believe that is the battery overflow - designed for clear battery overflow tube (that comes with a new battery) to slip inside of.  On my F's I always remember I could slide the clear battery overflow tube back and forth (up and down) when I replaced a battery.  I think it's designed so that you don't accidentally drop the clear tube off the battery when you pull a battery out to replace or service it.  It also directs the overflow to the opposite side of the bike than the chain is on.

 

[Mantree]

This is why agm batterys are nice lol

Sent from my SM-G900V using Tapatalk

[Jerry Rxman Griffin aka MuthaF'er]

Yes, going off of recollection, which is dangerous for me ....

I believe that is the battery overflow - designed for clear battery overflow tube (that comes with a new battery) to slip inside of.  On my F's I always remember I could slide the clear battery overflow tube back and forth (up and down) when I replaced a battery.

I think it's designed so that you don't accidentally drop the clear tube off the battery when you pull a battery out to replace or service it.  It also directs the overflow to the opposite side of the bike than the chain is on.

+1