Topic: Question regarding CB750 tubing?

[whitt_travis]

Slowly plinking away at a 76' CB 750F.  Previous owner didn't have much of a clue, and neither does my clymer manual, should have spent the money for a factory shop manual.

Anycrap... There's a nipple that comes off the top of the valve cover/top end of the engine.  I have a piece of half inch tubing that appears to have came off this area of the bike, however someone hacked it to the length of about three inches.  It's also stuffed with some kind of steel wool.

So, my question is, what exactly goes here (tubing, obviously), what dimensions, where do I route it to, and is there some kind of internal baffle that needs to be in the tube?

Thanks in advance, I searched both the forum and my clymer to no avail.

[TwoTired]

The engine internal air space must be of equal pressure to the outside environment.  The valve cover "nipple" is a vent that does just that.  The earlier bikes simply had a hose that may or may not have had a breather filter at the end.    It is better to have something that blocks insect entry into the engine while parked.  The breather tube allows blowby gases and other hydrocarbons to vent into the atmosphere on these earlier bikes.    Since breathing mammals often develop lung cancer and other diseases from breathing in hydrocarbons, the 750 F models were fitted with a breather element device that sucked these hydrocarbons into the engine intake and burned them, rather than simply dumping them into the atmosphere.  You may have heard of SMOG.  In the 70's this was a major issue.  If you enjoy brown air and contributing to a caustic environment, simply put a small filter on that hose or nipple, and dump that piston ring blow-by and oil vapor hydrocarbons into the lungs of society and breathe a sigh of relief.

Cheers,

[Steve F]

No baffle in the tubing, but if you still have the breather canister that's supposed to be mounted to the underside of the battery tray, that's where it's supposed to go.  Which nipple on the canister I'm not sure of at this point, but from there, there's supposed to be another tube that runs to the top side of the air box.  I'll have to look at mine to refresh my memory.

[spitfire]

Here's some pictures that may help.

Cheers

Den