Topic: CB750 K0 Breather Tube Routing

[Simpson]

Can somebody post a picture of how the tube runs through the frame correctly and how its fastened?

The shop manual leaves me scratching my head and the search on the site brings up nothing.

Thanks!

[City Boy]

Hi Simpson.Are you talking breather that exits from rear of valve cover?If so,hose sits over carbs and air cleaner housing,then goes down and sits between swing arm and rear of crankcase.There should be a rectangular hose guide bolted to rear of crankcase.Hose fits through that and terminates just below guide.Hope this helps.  Rock On

[Magpie]

I don't believe that guide is on the K0 motors and least not on the 2 I have. It's on my K1 and the overflow tubes for the carbs go through it but be carefull not to run them between the motor and the swingarm because it will pinch them and you'll have a hell of a time trying to figure out why your bike is running crappy at higher rpm. I think the vent tube from the valve cover follows under the backbone frame member, over the carbs and airbox then goes behind the airbox towards the swingarm. The smaller hose from the back of the motor goes to the oil tank breather odf the smae size. There's a larger vent tube off the oil tank that just goes down towards the swingarm as well. Hope this helps.
Cliff.

[Simpson]

Sorry I should have specified which breather tube.  

The big breather tube coming from the valve cover goes over the carb and air box.

It the runs down the back side of the engine to where???

It doesn't seem to fit between the swing arm and engine and there seems to be no guide or holder.

How does it exit out the bottom without blowing all over the swing arm and engine?

 

[MCRider]

Sorry I should have specified which breather tube.  

The big breather tube coming from the valve cover goes over the carb and air box.

It the runs down the back side of the engine to where???

It doesn't seem to fit between the swing arm and engine and there seems to be no guide or holder.

How does it exit out the bottom without blowing all over the swing arm and engine?

 

it just hangs there. Many will afix something to hold it still. Racers are often required to dummy up a catch can to run these open air breathers into.

As far as "all over the swingarm", the only thing coming out of there should be vapor. If anything accumulates you've got an engine problem. In constant high RPM racing environment you could get some drops to accumulate over time.

I think there is a metal loop attached to one of the 3 large case bolts at the rear of the engine to capture the ends of these tubes, breather, carb, and battery. It is often discarded (forgotten) in engine rebuilds.

The battery tube should go down between the engine and swingarm to the lowest point possible otherwise its fumes will degrade the finish on the swingarm and perhaps damage the chain.

[Simpson]

Thanks guys...

I'll "jimmy" it up he best i can.

Just got a new tube from yamiya and wondered what to do with the extra length.

The Honda manual shows it going down the swing arm.

[Simpson]

This is how I'm routing it right now. Look okay?

[MCRider]

The cam cover breather tube is kinda fat. It shouldn't be pinched shut and I just don't remember if it has enough room betwen the SA and the engine to keep from being pinched shut? If its not then you should be OK there.

It appears you don't have the tube holder that was bolted to the rear crankcase bolt. It would have been above the swingarm on the center bolt IIRC. It would hold all the tubes and allow them to stay together as they proceed downward.  Its not necessary, but helped in the routing.

[skidsolo]

I had this bracket on a 1976 K6 which is connected to the inside of the bolt for the right hand silencers. The cylinder head breather should exit through this on the right hand side. It's called out as the breather bracket.

[BenelliSEI]

Simpson...... I ran the same route on my K0. I think part of the problem is we are both using hoses with too much wall thickness that makes for a larger OD. I’m looking for something thinner.....

Where did you run the breather hose from the oil tank?

[PeWe]

I had this bracket on a 1976 K6 which is connected to the inside of the bolt for the right hand silencers. The cylinder head breather should exit through this on the right hand side. It's called out as the breather bracket.

My K6 hade that too, lost with the not wanted 341 pipes almost 40 years ago.
Check CMSNL charts. K2 had no  rear holder, shorter breather hose.

[BoneDigger]

Simpson...... I ran the same route on my K0. I think part of the problem is we are both using hoses with too much wall thickness that makes for a larger OD. I’m looking for something thinner.....

Where did you run the breather hose from the oil tank?

Breather tube from back of engine to the breather tube on the oil bag.