Clean out breather box?

[johnpaulmoore]

Hello all,

I inherited a 1981 CB750F that needs quite a bit of love. One thing that I came across that I couldn't find much literature on is the plastic black breather box under the battery carriage. I took out the plug from the drain hose, and all kinds of good stuff came out. Water, oil, white stuff, something that smelled like anti-freeze, a rubber chicken, etc. The question is should this box be completely cleaned out or is there a fluid or oil that is supposed to stay in there?

Thanks bunches!!

[LukeM]

That is a breather reservoir for the crankcase.  Moisture and some other vapors are collected there, and should be emptied on a regular basis.  I imagine every 2-3 months or whenever it gets full would be a good interval for this action.  It may mention it in the FSM.

Either way, it's not critical to the running condition of the bike.
Luke M

[Piute]

 My manuel says monthly @ Mr.Luke (know how much I ride) I'd clean it if you think of it ,I need the canister ,have cap think you can e a pic,so i know what the heck I'm looking 4,next time you clean it I'll put a filtering something on it fo now and let it be easyer to get to.thx

[LukeM]

If I read your post correctly, you do not have the crankcase breather canister.  You can let the hose from the top of the valve cover just vent to the atmosphere.  I can't imagine it would hurt anything.  Maybe Honda was trying to be environmentally conscious, by gathering up all the moisture and stuff and disposing of it properly.  Perhaps someone with a complete system on their bike could run theirs with the stopper out and see if it makes a difference.

I believe there's a mention in the FSM, or you could check www.bikebandit.com and see how all those hoses and stuff is routed.  

Luke M

[Re-run]

On my 78, I dont think I have that plugged at all but just let it go. I will have to look sometime to be sure though.

[johnpaulmoore]

Thanks everyone!

 

I found in the FSM where it says to drain it. I wasn't sure if there was supposed to be a layer of oil or something to catch dust. But after I looked at where it was coming from, if I have dust coming out of the crankcase, I probably have other problems, lol.

 

Re-Run, as I understand it in theory, I think there might need to be a plug in the tube to be able to drain in a controlled situation, and not blowing the bit of oil and other moisture vapor on your back wheel, brakes, etc. But there's probably so little, it may not matter. But I do remember when I first got the bike, the T-joint that feeds into the breather box was split and spewing air and a bit of oil. With it being right under the front of the seat, I would always come home smelling heavily of fumes and oil. I replaced the joint, and that fixed a lot of the problem. (I use the term problem lightly, as I'm one of those people that likes the smell of oil and gasoline. The girl, however, didn't. Well, that one at least.)

 

Thanks all for your help!! The engine rebuild is coming along nicely. Well, aside from the two seized bolts that I snapped the heads off of.

On Mon, Aug 1, 2011 at 3:45 PM, Re-run [via Honda CB750'S] <[hidden email]> wrote:

On my 78, I dont think I have that plugged at all but just let it go. I will have to look sometime to be sure though.

The ride IS the adventure. The destination is just to get gas!

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John Paul Moore

[sgtslag]

The only problem with letting it drip onto the ground, is that the hose may drip in the path of the rear tire...  For me, that cannister only needs to be emptied once every couple of years.  If it fills up, it can cause problems for the engine, as it will tend to push back into the engine.  If your bike is running rough, this is one thing to quickly, and easily, check:  pull the plug, and if a lot of crap pours out, fire up your engine again, and see if it runs better.  My father discovered his 750 Custom was acting up because its cannister was full; emptying the cannister solved his problems.

Riding in the rain, and running in high humidity conditions, will cause this cannister to fill up faster, according to what I read in my Clymer Manual.  After riding four long days in Canadian rain, for around 24-28 hours of driving time, there was nothing in my bike's cannister (emptied it before that trip, emptied it on day three of rain, got very little; emptied it when we got back home, four days later, and very little came out then, either).  YMMV.  Check it periodically, to get an idea how fast it fills up on your bike, and empty it according to your needs.  Cheers!

[Piute]

  I would not plug it ,I once pluged my breather on my Chevy 350 and blew a gasket ,I would either point to wards chain or put a filter on it ,H.D.s had those breathers and you dare not plug them,If you plug it let us know how long it last,lets save it and let her breath,  Piute N Judose

[Rodgil]

By having the plug in the end of the hose, the suction in the air cleaner housing will draw off water vapour and any corrosive fumes from your crankcase. If you leave it unpluged, it will draw air off the road instead, leaving the "bad stuff" inside your motor.

[shinyribs]

I new to bikes   so i dont claim to be an expert     any motor's crankcase needs to breath  ,you all know that,  as far as sucking dust or debris off the road,the breather housing on these bikes has a foam element to fiter any air that it might "suck in"    just cleaned mine tonight for the first time(sitting since 2004) and my foam was little more than crumbs      just replaced it with some foam i jerked out of the crack on an old truck seat     the breather really needs to be taken apart and cleaned   not just drained if bike has been sitting     i sure would not want my bike sucking in what i found in mine      spring loaded doo-dad inside keeps the foam filter in place     not a bad job