Topic: 1978 K8 Emissions Vent Breather Box

[Rosinante]

The words of this thread are designed to facilitate future Searches.  Plus, I have a question. 

This box is round and located below (actually attached to) the battery box.  It is about 3-4" in diameter.  It is pink and yellow striped.  Just kidding.  It is black.  It is not easy to see or reach.  As near as I can tell, there is a single fat hose coming out of the bottom.  I am unclear where this goes, but I think it just drains on the swing arm.  As near as I can tell, there are two hoses at or near the top.  One hose goes to the valve cover and the other hose goes to the top of the airbox (where the air filter is located).

Do I have this right?

[Bodi]

Not familiar with K8s but that seems correct for an emissions unit for the engine blowby. The top vent from the engine goes in, water vapor and oily stuff gets condensed in a filter like medium, I replace them with Scotchbrite pad on my bike as the OEM pad is NLA. The fumes go into the airbox via another tube and that usually turns the air filter black by where the inlet is. Condensate drains out the bottom onto the ground. The drain tube should have a "fishmouth" that lets liquid drain but doesn't let air get sucked in.

[Rosinante]

Thank you!  This is very helpful.  Further information:  The hose coming from the bottom of the breather box actually goes along an interesting path and then along side/underneath the right side (non-chain side) of the swing arm, more than half way to the axle, where it is cradled in a u-shaped piece of sheet metal, about 1.5 inches long, which is welded to the exhaust pipe bracket thingie.  So.....this hose is 18" long or so and does not drain where the rear tires might otherwise catch the drippings.  Engineers are smart.  Not all of them, but certainly some.  It does NOT have a fish-mouth (excellent descriptive term, BTW).  This probably means the box can breathe into that hose. 

Follow-up Questions:  Does this hose really need a fish-mouth?  If so, where could one be sourced?  Or how could one be fabricated?  What catastrophe will occur if there is no fish-mouth?

Also, as some of you know, I am preparing to synch carbs.  I am checking this box as part of my preparations.  Is there any reason to feel I need to 'fix' anything related to this breather box before I synch the carbs?

[Rosinante]

Ha!  The manual says there is a plug at the end of the drain hose which should be removed occasionally to allow drainage.  That's easy.  Golf tee might work. 

[BenelliSEI]

The original plug is plastic, with a small fin. In theory, your suppose to pull it out every so often and drain the condensation and liquid out. If you have a piece of filter media (I cut a square of Scotchbrite too) in the bottom of the box, justleave the plug out......

[madmtnmotors]

Sounds like you have it dialed in. The top hose goes to the air cleaner, the middle hose is from the vent at the back of the valve cover, and the bottom hose routes around the front of the swingarm and then back towards the rear and is held in place by a clip on the stock muffler bracket. Aftermarket exhaust would require an alternative means of securing the drain if you remove the stock muffler bracket.

Inside the chamber there is a plastic disk with holes in it. There is a lip inside the chamber that locates this disk in position and below this disk is where the filter media was originally placed. About all I ever find are small traces of the original media (if any) and I cut new filter media about 1" thick and 2" in diameter out of the green foam air filters designed for small Briggs engines. I'll pull the vapor canister every 15,000 miles or so to clean/inspect/replace the filter media. Put the filter media in the bottom of the canister and push the plastic disk down into the canister until it clicks past the lip partway down into the canister.

EZPZ 

[Jerry Rxman Griffin aka MuthaF'er]

The unit on my 75 CB750F looks different but is basically the same. I found that in attempting to replace that bottom hose it was not available. Don't know about yours. I did find that one from a 78 550K WAS available. Not sure about current availabilty. 17335-323-000 Tube assembly breather. It fits just fine. Length or tip may be different.