Topic: Breather Tube Lines. Where do they go?

[John G]

The parts book shows #10 breather line tube. There are three breather ports as shown in the pictures but I'm not sure where they go.

[Tracksnblades1]

See pictures..

[Tracksnblades1]

750 F s’  had this mounted up under the battery.

77-78k s’ may have also. Looks like they do..

[trigger]

The Breather cover one just vents to atmosphere and the route depends on what CB750.
The pipe at the back of the engine is part of the chain lube and goes to the oil tank 

[newday777]

The parts book shows #10 breather line tube. There are three breather ports as shown in the pictures but I'm not sure where they go.

What year, model is your bike John???

[John G]

Oops. It's a 1975 CB750K

[newday777]

Oops. It's a 1975 CB750K

Well my K5 is still tucked away for a few more weeks...

[Ellz10]

Buddy of mine milled this to hold my carb vent tubes (1st pic)

2nd pic is the catch can I made up and mounted.

Still thinking about how I want to go about the vent tube at the back.

[HondaMan]

The late (post 3/75 or so) K5 and the K6 had a unique breather tube setup for the top-of-engine and back-of-transmission hoses. They joined together with a tee, then ran all the way back to the right-side passenger's footpeg mount where a little sheetmetal bracket held it's end way back there. Many of these have become lost when someone "customized" their K5/6. It's main purpose was to reroute the oil vapor away from the back of the engine where it would build up and be difficult to remove, which came from the original top-of-engine hose ending in between the back-of-engine and the swingarm crossmember. The engines in those bikes that were assembled with the complex and long hose(s) [mostly] have a smaller spigot on the back of the transmission: it is only 8mm in diameter while the normal ones were larger, like 10mm and even 12mm. This seemed to be a production prelude to using the PCV canister in the later bikes.

[newday777]

The late (post 3/75 or so) K5 and the K6 had a unique breather tube setup for the top-of-engine and back-of-transmission hoses. They joined together with a tee, then ran all the way back to the right-side passenger's footpeg mount where a little sheetmetal bracket held it's end way back there. Many of these have become lost when someone "customized" their K5/6. It's main purpose was to reroute the oil vapor away from the back of the engine where it would build up and be difficult to remove, which came from the original top-of-engine hose ending in between the back-of-engine and the swingarm crossmember. The engines in those bikes that were assembled with the complex and long hose(s) [mostly] have a smaller spigot on the back of the transmission: it is only 8mm in diameter while the normal ones were larger, like 10mm and even 12mm. This seemed to be a production prelude to using the PCV canister in the later bikes.

I'll have to look at the K6 in my shop as I don't remember that being the case on my original K6 of a hose on the right side pax peg dump.
I do have that on my K8 though.
I know that the K6 has a different oil tank vent design from the K5 I have (10/74).

[BenelliSEI]

Buddy of mine milled this to hold my carb vent tubes (1st pic)

2nd pic is the catch can I made up and mounted.

Still thinking about how I want to go about the vent tube at the back.

How does your “catch can” vent?

[Ellz10]

Buddy of mine milled this to hold my carb vent tubes (1st pic)

2nd pic is the catch can I made up and mounted.

Still thinking about how I want to go about the vent tube at the back.

How does your “catch can” vent?

Hard to see in the pic, but I drilled holes in the top and situated a small bit of filter foam there.

[HondaMan]

The late (post 3/75 or so) K5 and the K6 had a unique breather tube setup for the top-of-engine and back-of-transmission hoses. They joined together with a tee, then ran all the way back to the right-side passenger's footpeg mount where a little sheetmetal bracket held it's end way back there. Many of these have become lost when someone "customized" their K5/6. It's main purpose was to reroute the oil vapor away from the back of the engine where it would build up and be difficult to remove, which came from the original top-of-engine hose ending in between the back-of-engine and the swingarm crossmember. The engines in those bikes that were assembled with the complex and long hose(s) [mostly] have a smaller spigot on the back of the transmission: it is only 8mm in diameter while the normal ones were larger, like 10mm and even 12mm. This seemed to be a production prelude to using the PCV canister in the later bikes.

I'll have to look at the K6 in my shop as I don't remember that being the case on my original K6 of a hose on the right side pax peg dump.
I do have that on my K8 though.
I know that the K6 has a different oil tank vent design from the K5 I have (10/74).

Yeah, the K6 can have any combination short of the PCV valve: Honda had quit making the K5 when the F0 came out and sales went down something like 40% for the 750. American Honda was screaming loudly for the 4-piper again, so by (I think it was) November 1975 the K6 was re-announced. I've worked on K6 bikes with modified F0 wiring, K5 wiring harness with the little F box under the steering head added, F0 disk brake, and other odd things. Inside the engine it gets even stranger: there can be F0 type pistons, K or F cam, and -392- heads over K bottom ends, or even F bottom ends under K heads, with the 1st and 2nd gears of the K engine installed (come to think of it, that one probably had the 4th gear of a K engine, too). This last combination made for a doggy performer, though, with compression numbers like 105 PSI cold: it had the F cam in it, too, opening intakes at 0 BTC. The sparkplugs ran white!

[newday777]

I looked at the K6 in my shop and sure enough it has the top hreather tube running down and out the right side framework past the passenger peg.

[PeWe]

K6 oil tank has no breather hose as the earlier.
The holder for the long breather hose from valve cover is rather expensive.
I lost mine many years ago.

Hose routed to passenger foot pegs.

[Gamma]

I’ve put a bottle on for the cam cover breather. It’s probably overkill

[Ellz10]

I’ve put a bottle on for the cam cover breather. It’s probably overkill

Ooo Gamma, I see that brake arm conversion kit! How do you like it??

[HondaMan]

I'd bet $$ that if the EPA sees this, they will pass regulations to make all SOHC4 bikes have one...

[Translations]

Speaking of breather tubes is there any concerns with just clamping a small filter on the nipple of the valve cover instead of routing a hose?

[Don R]

  A filter on the rocker cover will need cleaning once in a while. It will eventually oil soak from fumes. I tried venting the oil tank and valve cover into a high mount K&N type filter under the gas tank once. It was uneventful.

[Translations]

Good to know Don, with how easy it is to pop off and clean I am fine with that.

[PeWe]

I saw small K&N filters direct on valve covers in the 80's.
It must smell when waiting for green light.
 Hose from valve cover going down to at least foot peg will make better.
The long hose routed back to passenger footpeg as my K6 had seems to be not available .

[Gamma]

I’ve put a bottle on for the cam cover breather. It’s probably overkill

Ooo Gamma, I see that brake arm conversion kit! How do you like it??

It’s not been on the road yet, hopefully it will be good. It’s a Suzuki GT750 brake cable

[Stev-o]

I’ve put a bottle on for the cam cover breather. It’s probably overkill

Ooo Gamma, I see that brake arm conversion kit! How do you like it??

It’s not been on the road yet, hopefully it will be good. It’s a Suzuki GT750 brake cable

Does look really good, but curious why?

Thinking Honda wanted a metal rod to prevent possible liability from a cable break.

[Ellz10]

I’ve put a bottle on for the cam cover breather. It’s probably overkill

Ooo Gamma, I see that brake arm conversion kit! How do you like it??

It’s not been on the road yet, hopefully it will be good. It’s a Suzuki GT750 brake cable

I'd be curious to hear your thoughts after a few trips!

I’ve put a bottle on for the cam cover breather. It’s probably overkill

Ooo Gamma, I see that brake arm conversion kit! How do you like it??

It’s not been on the road yet, hopefully it will be good. It’s a Suzuki GT750 brake cable

Does look really good, but curious why?

Thinking Honda wanted a metal rod to prevent possible liability from a cable break.

I figured that was the only reason. I almost did one on mine, but opted to stay original there.