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1994 K75S Z Hose Question

Slipster

Slipster
Well I have been into the bike replacing rubber bits here and there. Just did a O Rings change in the starter, Alternator Monkey Nuts etc. etc. etc. I also found a tear in the Z hose. It ripped apart when I removed it. A new one is on the way. I cranked the bike over after putting it all back together again just to hear if the starter and alternator were ok. I had no Z hose installed. The bike starts but will not run.

So my question is one of better understanding what the Z Hose actually does and how that little hose can prevent the motor from running ?? IMPORTANT little hose :wow
 
It will not run without the Crankcase vent hose (Z hose).

The Crankcase vent hose does what its name implies. It vents the crankcase (into the intake plenum).

It vents it into the plenum above the throttle bodies AFTER THE AIR FLOW METER. Any air that gets into the plenum is unmetered air, meaning that the computer does not know it is there and does not inject enough fuel to compensate for it. Therefore, the mixture is way too lean to properly run. A similar situation will happen if you have the hose in place and remove the oil filler cap (happens on most modern cars too).

SMALL cracks in that hose will lean out the mixture enough to cause a multitude of problems (poor idle, burned valves, etc.) and that hose is VERY thin and in the hottest part of the bike. The cracks will happen just below the upper hose clamp and just above the lower hose clamp. These hoses usually require changing every couple years but need to be checked WAY more often ( at LEAST once a year).



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Thank you Lee for your detailed response to my question. I understand now and will definitely check the hose every year from here on out :rocker
 
It will not run without the Crankcase vent hose (Z hose).

The Crankcase vent hose does what its name implies. It vents the crankcase (into the intake plenum).

It vents it into the plenum above the throttle bodies AFTER THE AIR FLOW METER. Any air that gets into the plenum is unmetered air, meaning that the computer does not know it is there and does not inject enough fuel to compensate for it. Therefore, the mixture is way too lean to properly run. A similar situation will happen if you have the hose in place and remove the oil filler cap (happens on most modern cars too).

SMALL cracks in that hose will lean out the mixture enough to cause a multitude of problems (poor idle, burned valves, etc.) and that hose is VERY thin and in the hottest part of the bike. The cracks will happen just below the upper hose clamp and just above the lower hose clamp. These hoses usually require changing every couple years but need to be checked WAY more often ( at LEAST once a year).
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Hey Lee,

Mine has cracks in it. Do you have a part number?
 
Hey Lee,

Mine has cracks in it. Do you have a part number?

Hey, Lynn; that might be part of the reason you are getting poor mpg as posted in your other thread.

Mine was cracked as I discovered a couple months ago during another procedure---when I installed a new Z-hose it made a world of difference!
 
11 15 1 460 480 VENT HOSE $15.56
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Thanks, Lee.

My BMW dealer is not that far away from the local VA hospital, and I figured that I would hit both in one trip, or so I thought. I dropped by the dealer to pick up the hose, and, of course, they did not have it in stock. They only keep one in stock and it was sold last week. Just my luck.
 
I hope you ordered one, nonetheless! Among the best purchases one can make. :thumb

Yeah, I did. The nice thing was that my dealer did not consider it a special order, so I did not not have to pay for it yet. It just frost my rear end when dealers insist upon payment up front on everything. I can see it on clothing, helmets and such, but not on normal maintenance parts. Especially if it is something that they normally stock.
I understand why they do it, though.

A friend of mine who is a service manager suggested that we make one out of fuel line and metal fittings. I wonder, has anyone made their own?
 
Good question, Lynn and I know others have used certain larger diameter rubber hose to replace the Z-hose with---but if fuel line was used it would also have to be larger than the 8x13mm BMW standard. Check the ends for the correct diameter needed; might be in the neighborhood of 18-20mm is my guess.

Do not try the aftermarket Z-hoses (even the ones Beemerboneyard sells) as 98Lee advises us that they are even more flimsy than the OEM ones (and he is one who really knows of where he speaks).

But maybe a stout large diameter (truck?) fuel line would work just as well? On the other hand, maybe the Z-shape would require too much sharp bending, thereby cutting off the very pressure that needs to be vented in the first place. Interesting to see what the gurus say about this.

Don/Paul/Lee/Ted to the nearest white courtesy phone, please!
 
I think the hardest part of making a more sturdy replacement would be to also make it flexible enough that you could actually install it. There's not a lot of room there for larger diameter hose. That being said, if you can install it (and that's a serious IF) and it doesn't leak, it would work.



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I had the airbox eliminator on the 87 S that I owned and I only remember replacing that hose once. I think the eliminator really helped keep that over the engine area cooler, which made the hose last longer. Kind of a stretch for a reason for the eliminator, it did get a lot of looks.
 
Well, that $15 is just unfair....the K12RS only has the 'full distribution hose' unit available and the last time I purchased one it ran over $50 and now it runs over $75....usually it is just the Z shaped part that goes, but not always, but it is only available in the whole assembly these days. Still quite hard to replace.
 
Not yet officially on the market. Now looking at selling the K13S and getting a track bike. My wife is thinking maybe it would be good to sell all the bikes!?!?? We are about to list the Inn for sale as we begin work with our architects for our home in San Miguel de Allende, MEX. So, all this will take a while, but right now, theoretically both the K12RS and the K1300S are for sale, I will probably list them both in the next week on Craig's list, etc. I do have a line on a couple of good track bikes to cover me, but having to 'drive' to Sacramento weekly in a car when I could ride these wonderful roads is pretty tough to consider.....:violin
 
As a temporary fix to get you home, could you remove the hose and plug the opening on the plenum?

Yes, but you would get oil coming out of the crankcase end. Probably best to leave it in place and change it as soon as you get home. You'd open up more cracks taking it off. Small cracks for a couple hundred miles are better than big cracks for less. But change it ASAP.

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z hose replacement

is it possible to replace this hose without removing the gas tank and then the air filter. On my 94 k75 (naked version) it looks like the hose is jammed right underneath the air filter with no room to lift it off.

I am a proud new owner of this k75 so have a lot to learn!

Rob
 
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