Topic: Sandcast, KO and early 750 owners...

[Johnie]

I notice the breather hose that comes off the top of the engine ends near the swingarm.  As expected you get a little oil residue in that area.  I noticed on my 1980 & 1981 CM400's there is a plug in that tube that you empty every so often.  Can I put a plug in my KO breather and just drain it every so often so it does not drain on the swing arm area?  Or does this need to remain "open" all the time?  Or maybe I am missing the plug???  I can not recall if the later 750 models had that plug???  Thanks

[cafe750]

I wouldn't plug that hose up, because the crankcase has to vent. You could run a longer hose though, so that you can route it with the end of the hose below the swingarm, and it wont make as much of a mess.
Hope this helps!

[754]

Hose goes oil tank.

[Clyde]

If by the top of the motor, you mean from the valve cover- this is about a half inch diameter hose and should vent below the swing arm. I would do as suggested above and extend it to below the swing arm. These older engines do need more vent than a newer engine and I would certainly leave it open.
The small pipe from the back of the gearbox goes to the oil tank.

[c_packer]

I installed an automotive breather pod filter to the end of mine, and made a bracket to hold it below my carb pods. I don't think it helps or hurts, but it really looks neater than a loosely hanging hose. Kind of looks like a fifth carb.

[MCRider]

Hose goes oil tank.

Working from distant memory here so I may be wrong...
On the older bikes that hose was just vented to the atmosphere, like a crankcase breather on an old car. As years passed and emmissions rules became tighter, factories began to recycle the fumes from these hoses into the airbox for redigestion or as you suggest to a spigot on our oil tanks, above the level of the oil. But I don't think the very oldst bikes had that spigot.

A catch can of any sort is a fix for the older bikes, but it should not be blocked off unable to breathe.

[754]

Yeah , I got it wrong, I thought he meant the one on the rear of the motor..

[Markcb750]

My '76 crankcase vents to the swing arm area, real mess there after 32 years.

PO has cut the hell out of lower airbox cover, warped and cracked so it needs replacement.

Looking for replacement parts I find  the '77 airbox has a connection port for the crankcase vent at the top of the airbox.

Has anyone tried to install this airbox on a '71 to '76 CB750K?

Thanks
Mark

[lordmoonpie]

I haven't done this yet on my 750 build but the same thing is needed for the CB450 I have. I take this off into a catch tank located on the front frame brace (takes in all three vent lines from the 450 and this has an open vent at the top to keep it atmospheric pressure. It also has a drain screw at the bottom to allow it to be emptied once in a while. The tank itself ways nothing at all and is a wonderful bit of engineering. It came from www.tga.co.uk and can be seen in this picture below just in front of the engine and below the first bend of the exhaust headers...

[KingCustomCycles.com]

Sweet attention to detail and quality! 

[chrislib]

I hear ya on the mess. When the cold comes I plan on trying to fab up a catch bottle that`ll hold the liquid but still allow the crankcase to vent. Sort of like this
http://www.dieseltruckresource.com/dev/showthread.php?t=199914&highlight=catch+bottle
but obviously on a much smaller scale. (I`m a member over at that board also, my daily is a cummins dodge)