Throttle Problem '87 K75S

[mgalie]

So, I just bought my first bike; an '87 K75s. Among the numerous maintenence issues I noticed was a sticky throttle. It being November and still 60 degrees, I quickly ordered a new cable and replaced it. That did not solve the problem, and it may only be worse. The old cable would at least slowly slide back. The new one will hold it's position most of the time. Does anyone have any ideas/suggestions as to what the problem could be?

Also something that's been bothering me; I've found two hoses on the bike whose purposes are a mystery to me. The first mystery hose comes out of the engine case at the front middle. I suspect it's the breather hose, but what really puzzles me is that someone decided to stuff a screw and washer in the end of it. I suppose that ought ot be removed, huh? The second hose goes through the transmission and doesn't appear to connect to anything. It has an elbow on top and goes clear through the tranny and sticks out on the pavement side. It slides freely and has no apparent connection or purpose. I cannot find either of these hoses in the drawings in my Clymer manual or on an online OEM schematic. Can anyone solve this?

Thanks,
Michael

[DrPaul]

Michael,
Wow! I just bought an '87 K75S and have had it apart cleaning, repairing and replacing various parts (see my thread "NEW" old K75S). The throttle on this bike has a passive return system meaning there is a single throttle cable and the TB shaft requires spring action to close. It may be binding on something. See if the cable pulley on the TB shaft is rubbing on one of the #3 boot clamp (mine did after reassembly) and I simply loosened it and rotated the clamp enough to let the pulley move freely. Also be sure the return spring is there and working.

Mine has the same 2-3" piece of tubing sticking up from the front of the engine case with a screw in it. Must be OEM for something. Same with the vent tubing back by the tranny. I'd like to know more about these tubes as well.

Paul

[PGlaves]

OK! Here you go! Back when those bikes were built BMW thought it was a good idea to vent the fuel tank directly to the crankcase. There was a small one-way valve in the hose to allow tank pressure to enter the crankcase but not allow crankcase pressure to blow back. Great theory.

What happened in real life was that sometimes an overfull fuel tank would discharge raw gasoline directly to the crankcase. I never heard of any cases where anything actually blew up - too little oxygen content in the crankcase probably - but did hear of several cases where the gas diluted the oil to the point of engine damage.

I bought my K75 in early 1986 and the dealer disconnected that vent line at the 600 mile service.

To close it off folks have used a variety of methods. Some just leave the little plastic valve in place. Others put a cap over the little stub pipe. Without a clamp it can blow off though.

Some folks just screw a screw into the end of the hose - which is what you found.

The second hose with the plastic "L" on the end is a battery vent hose. Either it is disconnected and ought to be reconnected to the little hole in the left end of the battery in the black part near the top - or you have a "maintenance free" battery that doesn't use a battery vent line but the installer just left the hose sitting there.

[byker]

Does this vent hose apply to an 87K100rs?

[jdiaz]

So, I just bought my first bike; an '87 K75s. Among the numerous maintenence issues I noticed was a sticky throttle. It being November and still 60 degrees, I quickly ordered a new cable and replaced it. That did not solve the problem, and it may only be worse. The old cable would at least slowly slide back. The new one will hold it's position most of the time. Does anyone have any ideas/suggestions as to what the problem could be?


If the throttle assembly is pushed too far onto the handlebar, the inside of the throttle grip will rub against the end of the steel handlebar and make your life miserable.

Remove the switchplate (the one with the kill switch), loosen the allen bolt, and slide the throttle assembly out a couple of mm. That will probably improve the action a bit.

[jdiaz]

Does this vent hose apply to an 87K100rs?

Yes, but only on US bikes. Canadian bikes wouldn't have this emissions system because you don't have the Californian clean-air folks to accomodate. :laugh

[mgalie]

Thanks everyone! And especially jdiaz; the assembly was just up too far up on the handlebar. As simple as that.

[jdiaz]

Glad it was that simple!!

[BubbaZanetti]

Glad it was that simple!!

nice to see you being helpful:D

[nh7robmw]

If the throttle assembly is pushed too far onto the handlebar, the inside of the throttle grip will rub against the end of the steel handlebar and make your life miserable.

Remove the switchplate (the one with the kill switch), loosen the allen bolt, and slide the throttle assembly out a couple of mm. That will probably improve the action a bit.

I know this thread is kind of ancient but searchy "sticky throttle" and finding this post solved my problem (throttle was sticky after right-side tipover).

Thank you!