Throttle slack once parked after perfect ride?

[Brahma]

Hi-

For a variety of reasons, I haven’t ridden my trusty K100RT I have owned for 37 years for over a year. 

Every few months I have let it run for 20 or thirty minutes, and when I “parked it”, that was done with all new fluids, new battery and on a trickle charger.

I wanted to take it for a long-awaited ride, but noticed it needed new tires. This past weekend, I rode it for the first time to the dealer for its appointment for new skins. It rode to and from that appointment- 15 miles in total- like I had never parked it.

I got up early the next morning to go for a ride, and for the first time in 37 years, it wouldn’t start- just cranked, and cranked and cranked.

Heart-broken, I did notice initially that it “puttered” as if it wanted to start, but couldn’t.

After the decades of ownership, I “know” that the choke (which I rarely ever have needed to use) was working normally and left “off”.  The cable at the TPS sensor/switch showed the choke actuation.

I let the bike sit overnight then again tried to start it. I always have pressed the starter button half-way twice to cycle the fuel pump before actually started it. It again p
“puttered” then nothing but strong cranking. Since I now new it probably was a fuel problem- it was initially trying to fire, I let it sit again to allow me to think.

The next day I attempted again, but this time while cycling the fuel pump before starting, I twisted the grip fully twice, then hit the starter, and VROOM!- it started and ran normally!  Very happy, I let it run for a few minutes then turned it off. 

To me, it seems as if there is sudden “slack” with the cable, where I have to really open it up just to get a normal start. I don’t know how a “slack” condition could even be possible. Also, the throttle pull seemed somewhat heavy- and I’ll immediately theorize sitting for so long didn’t help that symptom.

My overall question is how to attack the symptom of “throttle cable slack”, and how after riding completely normal to and from somewhere, it happened just by parking it?

The only thing I can think of is throttle handle position moved- but during parking?

Weird, but at least it ran. I’ll keep you posted but comments are truly welcomed.

I have new tires waiting to be broken in!

Thanks-

Brahma

[The Mighty Gryphon]

First thing that comes to me is that the throttle butterflies are hanging open,  That will let too much air in the cylinders to start the engine and make the throttle feel slack.

Look at the quadrant down at the throttle bodies and see if it is coming down on it's stop. 

[Brahma]

Good point- didn't think about that.

Whats the proper lubricant? WD40?

[Laitch]

Along with lubricating the throttle cable plate Gryphon describes, it could be that the throttle gears that mesh together within the throttle housing have one or more teeth that have worn down enough to slip until rotating the throttle brings undamaged teeth into contact. That condition will cause slack in throttle movement, too. Those gears need regular lubrication.

How does the half-press of the starter button work for priming the pump? Are you doing that while the starter is cranking? The fuel pump on a 2V K doesn't use priming; it's pumping as soon as the crank starts rotating. Are referring to fuel enrichment by pressing the button?

[Brahma]

Yes, the throttle is the first thing I'll lube.  I've always kept it well lubed, but it's due...  My description is inaccurate, the fuel system certainly operates/cycles/is energized by half pressing the starter button.

[The Mighty Gryphon]

Lars, I think he's doing a quick stab on the start button.  I will do that as well when starting on a cold morning after a long idle period to pressurize the rail.  It helps make the engine fire instantly without having to crank the engine for a second while the rail builds fuel pressure. 

The idea is that you press the start button to trigger the fuel pump, but not long enough to crank the engine.  The pump runs for a second without actuating the injectors because the Hall sensors aren't being triggered by engine rotation.  Works great.

[The Mighty Gryphon]

Brahma, you should be able to see the throttle quadrant by removing the left knee pad. 

Normally, the quadrant is pulled up by the cable and returned to rest on the the idle speed set screw by a spring.  That you feel slack in the cable says that the quadrant is hanging up and the cable isn't feeling the tension of the return spring.

If it isn't returning to the set screw, it will be holding the throttle butterflies open.  This is going to affect starting the same way holding the throttle open does.  Too much air is going to go into the engine to make it fire.  This is why the owner's manual advises to leave the throttle alone when starting.

[Brahma]

Can you guys recommend anything better to lube up throttle body linkages besides WD-40?

[Laitch]

The idea is that you press the start button to trigger the fuel pump, but not long enough to crank the engine.  The pump runs for a second without actuating the injectors because the Hall sensors aren't being triggered by engine rotation.  Works great.

You're describing millisecond maneuvers that shouldn't be necessary at all in a well-maintained engine, even if they were effective. Are time constraints so great out there that a couple of extra cranks or lever movements create scheduling chaos? In cold weather, I set the starting speed lever at first or second stop, start the engine, ride off, and close the lever 400 feet later before the first downhill turn in the road. After that, it's smooth running. Stiff oil in the transmission at cold temperature is the only constraint in the competition for reaching the first pothole field in the road before another neighbor does.  Riding the hell out of the Brick and regular maintenance are all it needs; besides, I'm benighted enough to actually believe what the LE Jetronic manual, maintenance schedules and the endless stories of mechanical or experimental failure within my riding cohort are trying to tell me. 

Admittedly, after the snow stays in November, I do the last maintenance of the season—which could include valve clearance check and throttle body balance depending on the mileage ridden in the prior months—then it's up on its center stand with a full tank of fresh, conditioned E10 and a disconnected battery negative cable. It isn't caressed again until April. I wouldn't intermittently run the engine during that six months or so of idleness unless I was lovesick for the sound of its thrumming because all I'd really be doing would be creating an environment for condensation to infiltrate the oil and electrical connections. I don't want that happening because I want to ride hard in spring the first day mud has disappeared and the roadbed has hardened. I'll change the engine and fork oil, when—or if—I return. 

[Laitch]

Can you guys recommend anything better to lube up throttle body linkages besides WD-40?

Teflon spray, silicone spray, dry lube combination sprays, machine oil. It shouldn't take much. Work the throttle occasionally if you're not riding the Brick often enough; it's okay to go vrroom, vrroom when you do.

I use WD4O for cleaning electric connections and tools infiltrated by water; it isn't used often.

[Brahma]

Got back to it late last night and this evening. pulled the left lower, checked the throttle body, TPS, choke and throttle movements. Lubed the TB linkages with spritzes of silicone spray, opened up the throttle handle cleaning old gummy grease, and re-lubed. Throttle now snaps closed properly.

Still won't start normally- have to twist the throttle wide open when starting, it catches and starts and I immediately close down the throttle and it idles normally.  Same procedure to start every time.

Gas tank is 2/3 full, with year old gas.  Yeah, I know- that doesnt help. Gonna get fresh tomorrow. Fuel filter probably could use to be changed- I'll procure one tomorrow.

[Brahma]

Ordered parts since the last post- fuel filter, TPS and fuel pressure regulator. Waiting on the last two from der Fatherland.

* changed the fuel filter, siphoned the old gas out, replenished with fresh.
* primed the pump- took a few cranks to get the new gas through the filter.
* Still, only started after I twisted the throttle wide open while cranking, then closed the throttle immediately when it came to life.
* let it run and warm up, idling for about ten minutes.  Once started, idles and runs normally.
* shut it down, let it sit for about five minutes
* would only start again after cranking and twisting the throttle wide open.

Thoughts?

Video of it idling normally-

[The Mighty Gryphon]

Have you checked for air leaks around the throttle bodies and their bushings?  What is the condition of the crankcase breather tube A.K.A. "Z" tube?  How old is your "Z" tube?

Hard starting is often the result of an air leak or a bad engine coolant sensor.  If not those, it could be a problem in the starting mixture provided by the Jetronic unit.

What may be happening is that the engine is not getting a rich enough mixture to start.  You open the throttle and crank.  The engine won't start, but the cylinder is being filled with fuel that will fire when the throttle is closed. What you may be doing is essentially precharging the cylinder with fuel. 

[Brahma]

I agree with your consensus with fuel loading, but this, whatever it is, literally happened overnight while parked, after probably the sixth different person in thirty-seven years- unbeknownst to me- took it on a "test drive" at the dealership, and then "washed it".

Again, it started, rode to the dealership, and back again seemingly fine. After parked in the garage overnight, it hasn't started properly since.
.
* I highly doubt that there is any air leak at the throttle bodies.
* All the vacuum lines around the fuel rail/throttle body area don't look bad or disturbed.
* I'm not sure how the temp sensor is involved if it happens when cold, or after warmed up.

This bike ALWAYS started immediately for nearly four decades. Please keep the ideas coming.

[Martin]

Once the bike is warm and idling press the green starter button ( the starter will not engage). If the mixture is lean the revs will increase, if the revs drop or the engine dies the mixture is rich. If the mixture is correct the revs should stay the same or slightly increase. A faulty temperature sensor  will allow an incorrect mixture normally too rich which will cause flooding and non-starting.
Regards Martin.

[Laitch]

. . . literally happened overnight while parked, after probably the sixth different person in thirty-seven years- unbeknownst to me- took it on a "test drive" at the dealership, and then "washed it".

Remove the Jetronic plug and bathe it with compressed air; likewise with the ignition control plug. When the Brick was washed, spray could have compromised electrical connections somewhere, especially if the rinse water was under pressure. Brick electrical connectors can be sensitive. Treat the coil connectors also. This is the only condition where I'd recommend WD-40 as a treatment but would prefer to use DeoxIT D5.

[daveson]

I was also wondering if for example the fuel injection control unit isn't getting a cranking signal (which should include an enriched mixture if the engine is cold)

While you haven't been riding it you occasionally let it run for 20 or 30 minutes. If that's at idle on the centre stand, I don't think that's good. Yes it's water cooled but parts of the exhaust system might be getting too hot.

A few other unlikely thoughts.

1. Does it start normally with the throttle position switch unplugged?

2. Does it start normally with the air snorkel removed?

3. It started normally before you took it to the dealer, go back and get the old tyres put back on to see if it then starts normally again.

All three are unlikely but at least the first two are more likely than the last thought, I thinks.

[Brahma]

Hard starting is often the result of an air leak or a bad engine coolant sensor.  If not those, it could be a problem in the starting mixture provided by the Jetronic unit.

I do believe we have a winner. Found a k75 video on Youtube with my exact symptoms (below)

* BMW lists part 61 31 1 459 197 "Temperature Sensor as the dreaded "N/A". Ordered one from Euro MotoElectrics picturing a BOSCH stamp on it. Will replace hopefully next weekend.

[frankenduck]

Every few months I have let it run for 20 or thirty minutes, and when I “parked it”, that was done with all new fluids, new battery and on a trickle charger.

This is a bad idea. The majority of engine wear is caused by cold engine starts.

Letting K bikes idle for extended periods will foul the spark plugs.(Worse on K75s than K100s for some reason.)

BMW recommends riding off immediately after starting.

From the owner's manual:


You're just wasting gas and causing climate change. (or so they say)

[Brahma]

This is a bad idea. The majority of engine wear is caused by cold engine starts.

Letting K bikes idle for extended periods will foul the spark plugs.(Worse on K75s than K100s for some reason.)

BMW recommends riding off immediately after starting.

From the owner's manual:


You're just wasting gas and causing climate change. (or so they say)

I've owned and operated this same bike almost a decade longer than the people who wrote the manual possibly spent an entire career at BMW, but thanks for the input.

[frankenduck]

I've owned and operated this same bike almost a decade longer than the people who wrote the manual possibly spent an entire career at BMW, but thanks for the input.

The German version of that manual was written in 1982. How do you know the age and experience of the authors and engineers who wrote it?

If you've been around so long then you should know that cold starts cause a majority of engine wear.

What possible benefit is there from idling a vehicle for 20-30 minutes every two months?

[The Mighty Gryphon]

If you've been around so long then you should know that cold starts cause a majority of engine wear.

What possible benefit is there from idling a vehicle for 20-30 minutes every two months?

First, you are correct about cold starts.  But, the wear pretty much stops as soon as oil reaches the cam lobes, usually within 2 seconds max.  Once the oil flows, wear essentially goes to zero.  I supplied test equipment to a GM engineering lab that was testing life expectancy of overhead cams.  With proper lubrication(correct viscosity and temperature) cams lobes can go well over one million miles with no discernible wear. 

Testing for cold start wear showed that oil flow delay was a major factor in wear on cam lobes and followers.  Oil delay is mainly a function of cold viscosity.  In the 30+ years since I saw these tests, lube oils have gotten lower cold viscosity while at the same time maintaining or actually improving the film strength which is the thing that prevent metal on metal wear.  Modern 0W and 5W oils flow much faster to where they are needed and have virtually eliminated lobe wear in modern engines.  The film strength of modern 5W synthetic oils is better than many of the heavier oils of the era when our bikes were new.  I have been running Quaker State 5W30 Full Synthetic for six years now in my bikes with no problems or cam wear.

Yes, engine parts wear out, but that is normally due to low sump levels which delay oil flow, Worn out oil, and overheated oil which has broken down the molecular chains and lost it's film strength.  Keep the oil at the proper level and the engine at normal operating temperature and wear will be zero.

Second, idling a stationary engine will do little damage.  It is essentially the same as being stuck in very slow stop and go traffic.  About the only issue is the heat of the headers and the cylinder head which does get some cooling from air flow.  Periodic running to charge the battery during extended periods of non-use is mainly a waste of small amounts of fuel.  A trickle charger is probably a more efficient way to keep the battery charged.

[frankenduck]

First, you are correct about cold starts.  But, the wear pretty much stops as soon as oil reaches the cam lobes, usually within 2 seconds max.  Once the oil flows, wear essentially goes to zero.  I supplied test equipment to a GM engineering lab that was testing life expectancy of overhead cams.  With proper lubrication(correct viscosity and temperature) cams lobes can go well over one million miles with no discernible wear. 

Testing for cold start wear showed that oil flow delay was a major factor in wear on cam lobes and followers.  Oil delay is mainly a function of cold viscosity.  In the 30+ years since I saw these tests, lube oils have gotten lower cold viscosity while at the same time maintaining or actually improving the film strength which is the thing that prevent metal on metal wear.  Modern 0W and 5W oils flow much faster to where they are needed and have virtually eliminated lobe wear in modern engines.  The film strength of modern 5W synthetic oils is better than many of the heavier oils of the era when our bikes were new.  I have been running Quaker State 5W30 Full Synthetic for six years now in my bikes with no problems or cam wear.

Yes, engine parts wear out, but that is normally due to low sump levels which delay oil flow, Worn out oil, and overheated oil which has broken down the molecular chains and lost it's film strength.  Keep the oil at the proper level and the engine at normal operating temperature and wear will be zero.

Second, idling a stationary engine will do little damage.  It is essentially the same as being stuck in very slow stop and go traffic.  About the only issue is the heat of the headers and the cylinder head which does get some cooling from air flow.  Periodic running to charge the battery during extended periods of non-use is mainly a waste of small amounts of fuel.  A trickle charger is probably a more efficient way to keep the battery charged.

He mentioned that the has a trickle charger/maintainer hooked up so that's a non-issue.

Oil does distribute quickly but does not a reach optimal viscosity until it warms up to a decent temperature.

That's an impressive amount of typing on your part but it still doesn't answer my basic question: What possible benefit is there from doing this?

[The Mighty Gryphon]

First of all, I wanted to counter your comment that running the engine was bad for it. 

Second, oil flow on cold start with modern low viscosity oils is almost instantaneous.  The chemistry of modern synthetic oil is much better than the oils available when our bikes were new.  Film strength is also much better.  A film that is only visible with fingerprints will protect the contact surfaces of the cam lobes and followers on cold startup.

The reason I run my bikes every couple of weeks during the winter is to dry the engine both inside and out.  Winter here has temperatures that cycle up and down a lot.  When I see the garage floor wet with condensation I run my engines long enough to get 3-4 fan cycles to heat the engine.  This not only dries the engine, but also cycles the injectors, refills the oil galleries, replaces the oil film on bearing and gear surfaces, and charges the battery.

By doing this every 3-4 weeks, the oil flow on startup is a lot faster and oil film is better than a startup after a 5 month idle period.  It goes along with the idea that long idle periods are not good for engines and other mechanical things.

I apologize for the long post, I was trying to convey some of what I have learned from the automotive engineers I worked with over the years.  Even if you didn't learn anything maybe someone else did. 

[Laitch]

First of all . . .

This is a bad idea. . . .

It seems we’re neglecting the fact that Bramha has more experience with his Brick than possibly the individuals with entire BMW careers who developed it and composed the Brick's manuals. We actually should have been asking him what to do about his Brick’s problem rather than he asking us.  This turnabout is as astonishing to me as my first sight of the Grand Canyon from a Rt 66 highway pull-off outside Williams, Arizona in the Fifties.