Just had a two day trip on the '85 K75C. Went east to west from Linc's to mid-wales coast. Did about 280 miles Wednesday and about 260 today. The bike went well apart from some odd behaviour after resuming my ride home with about 40 left to do (so had done until then about 500 miles over the two days before).
After restarting the bike after a stop that was maybe 35mins (so bike still warmish afterabout 120 miles since last comfort break_) the bike almost died at the junction and them at a few sloe bits thru a town where revs were about 2000 or less, seemed to stutter and going to not idle. Managed to keep going and then nearer home so about 10 miles away it seemed fine again and idled as normal. Any thoughts? The 'throttle position' sensors wires all attached. When at home the battery on charge / conditioner but not whilst away and don't know how old but seemed to start OK each stop.
Anyone experienced anything similar or thought what could have caused the problem at these low Rev's and around the time when it would idle. Mark

Fuel tank connector on the fritz?

Where or what part is that?
Did have the BMW tank bag on so wondered if that might have caused it stopping air.
What connection do you mean and how to check?
Mark

Comes out from under the back of the tank and connects on the right side.

four wires:

Green/white - fuel pump power
brown - ground
white - idiot light
yellow - fuel gauge

Fuel tanks were changed in 85. Some have the connection at front left, but these have the 4 and 7 litre warning lights. The 4 pin connector at the front is well prone to trouble. You can open out the male pins with a small precision screwdriver which will make for a more secure connection. These tanks seem to have the single screw holding them down.

My LT has the later tank and the connections are rear right. I think it uses the same type of connector but mine had been modified [ex police bike] and had a 4 way connector behind the frame diagonal, accessible by taking off the side panel. Colours are same as Duck wrote.

I don't know what the manufacture date was for the K75C so its quite possible it only has the later one as Duck says.

My LT did something similar at one point and turned out to be a spark plug gone wrong, one with only a few hundred miles on it.

All K75s have the later fuel level sender.

I had a failing fuel pump show similar symptoms but the connector is the first place to check.
The connector on my K1100 was so bad that I ended up replacing it with a 4 pin plug from the auto shop.

Checked connections and they seem OK.
As mentioned hasn't reoccurred.
Will look to check pipes in tank and replace fuel filter.
Is a pump something which will fail overtime or just stop working? It ran/runs OK otherwise so assume that was OK and the pressure thingy.
Apart from that hiccup bike went really well, seemed it was giving about 58-60mpg too, which seemed good.
M

I've had a sort of similar problem yet to be resolved. You can read my thread here.
Like to hear if you think there is some similarity.
Cheers

Captain Holister wrote:I've had a sort of similar problem yet to be resolved. You can read my thread here.
Like to hear if you think there is some similarity.
Cheers

I am not sure this is quite the same issue. My issue didn't involve the clutch....just when I needed bike to idle it was about to die unless I blipped kept the revs up.

What happened is once the revs got to a point with closed throttle and needed bike to idle, it didn't and almost died. Ran as if it was going to die for some miles at the low revs i.e. at junctions/in town as if there was no idle ability. Then a few miles further on (about 25) in the next town seemed fine and did idle at traffic lights/junctions, as if no problem.

What I found very odd is that I had ridden over 260miles one day and absolutely no symptoms or problems; then rode around 185 miles or so second day with three comfort stops and riding thru a number of towns with junctions. All was fine until the last coffee/comfort stop. Bike started fine it was only when pulling away and riding out of the car-park and then at a junction it faltered as if it was about to die. Ran "iffy" for a few miles with same symptoms at junctions in very slow moving traffic, and then later (after I say about 25miles) it seemed ok again....very odd. 

I have checked (what I think) is the fuel connector and the connections to the TPS and they seem ok.

"Choke control" seems to work - on handlebar, or did during last rides.

Battery back on tender (Optimate) and seems to be holding charge, and didn't take long to go 'green' which suggests to me battery is 'ok' I did think that perhaps it was low on charge or a problem...but again having had no symptoms previously not sure that it's that.

I do know the tank had been off during it's recent 'work'; but as I mentioned had run many hundred miles before this without a problem AND that included many stops/starts and bike sitting out overnight...and many miles before the problem.

Fuel possibly lowest it's been (had done about 165 miles when it occurred) but it regained composure after running a while.

Fuel seems to be pumping and working ok at other speeds, and bike starts ok - so I assume my problem may not be a bad fuel pump or filter. Maybe a poor assumption....maybe someone with more experience can advise

Crankcase/engine breather seems pliable and doesn't appear to have any splits or cracks.

Rubbers around inlets all seem fine too, not perished or cracked.

I wonder if previous owner replaced these at some time--they don't look really old.

I am going to change the spark plugs (to NGk D7EA [7912]) as I don't know when these were last changed and see if there is a repeat, or if that helps. Changing plugs wont be a bad thing; especially as I don't know when they were last changed.

If it reoccurs I may then look at the following, but not sure what order - but only one at a time to not confuse myself more by changing a whole load of things...:

1. Replace Fuel filter (again don't know when that was last renewed)
   
2. Hoses in tank connecting to pump
   
3. Fuel pressure thingy
   
4. Ignition leads (I seem to recall some test to check these, maybe can find something on the forum about this)
   
5. Fuel pump....(starting to get expensive.....!)
   

A bit of a mystery....but doesn't sound exactly same as your symptoms.

Regards

Mark

Been out for a short ride, about 40 miles.
After running for about 6 miles the bike did idle but very low and generator light came on, but it didn't die. This was at a fuel station and filled up.
Ran again for the other 35 miles and stopped at every junction and saw if bike idled and it seemed to around 750/800 rpm.
When got home did notice a round rubber pipe just above the tps did seem old and a bit cracked-will have to see what that's for....
But no repeat of it wanting to die, apart from the stop after the first few miles.
Still not convinced it's not going to reoccur.
M

mhsilverw wrote:When got home did notice a round rubber pipe just above the tps did seem old and a bit cracked-will have to see what that's for....

Crankcase ventilation, change it....if it leaks you get unmetered air in the intake
and running problems.....this hose have a rather short average lifetime.

I think it's this part....

11111460283

Is that the bit you mean. Could that be responsible for the iffy running at idle?

Mark

mhsilverw wrote:I think it's this part....

11111460283

That is a short metal tube which the crankcase ventilation hose (at the red arrow
in my picture) connects to.

11151460480

Inge K. wrote:

mhsilverw wrote:When got home did notice a round rubber pipe just above the tps did seem old and a bit cracked-will have to see what that's for....

Crankcase ventilation, change it....if it leaks you get unmetered air in the intake
and running problems.....this hose have a rather short average lifetime.

ok, thx - that is the pipe that seems a bit cracked. Will change it and see if that makes a difference - sounds like it could be the culprit for the idle issue I am suffering.

Will let you know if that solves the problem.

Mark

I have just replace that crankcase vent hose on mine. It was very badly split and gaping at both ends but I had none of the symptoms you've been getting. I was getting quite a bit of back firing due to extra air being sucked in.

Idle should be 900rpm.

Your intermitant rough running and poor idle sounds like possibly there's a bit of water in your tank.

When this pipe is cracked, the engine will run crappy on idle. Just to get an idea how bad it could be, try opening the engine oil cap.

About the battery, I had a similar problem. After a short stop at a store, the bike was dying on idle but running great over 2,000rpm. At the time, the battery seem to be strong and had no problem to run the starter.
The red light on the dash never flickered.
Back at home I was trying to troubleshoot when the battery went totally flat.   
I took the one from the K75 and it solved the problem.
The whole problem was a faulty battery even if it seem strong. It was delivering power only when the demand on power was high (running the starter).
Why the bike ran fine over 1,500/2,000 RPM? This is because the alternator is only working above 2,000 RPM and It delivers enough power for the ignition/EFI without the need of a battery.

About the battery, a mechanics told me that he saw the same problem with a battery having a bad cell.

Captain Holister wrote:I have just replace that crankcase vent hose on mine. It was very badly split and gaping at both ends but I had none of the symptoms you've been getting. I was getting quite a bit of back firing due to extra air being sucked in.

Idle should be 900rpm.

Your intermitant rough running and poor idle sounds like possibly there's a bit of water in your tank.

Hi
I may have had a backfire too, I thought I had driven over a discarded carrier back at one junction but from your comment wonder if this was actually a back-fire.
I hope to acquire and fit a replacement and see if that makes a difference before looking elsewhere; although from the other post maybe I need to add a battery to my list of things...at this rate I'll nearly have a 'new' K!
I am hopeful my limited skills will enable me to swap this vent-pipe out....and will keep fingers crossed.

Apart from this "idle issue", the bike f(or one approaching 30yrs old) went very well; seemed to be getting about 58mpg and it didn't disgrace itself in company with a newer 955i Triumph Sprint. That was faster, obviously on the straights, but the K was happy to keep up/make a pace that was comfortable (and lawful!) and talking of comfort was great with the low seat and the 'C' bars - whereas my friend on the Sprint seemed to have a bit of cramp in the legs and a bit of wrist ache (although the Sprint hasn't clip-ons - the bars are more aggressive than on the 'C'!). I also find the combination of the 'C' bars and low seat a little more accommodating my frame than a K75S (I had tried before). I expect someone taller and more 'bendy' might prefer the 'S' - horses for courses perhaps.

I will persevere with the K for a while as it does seem to make a nice 'companion' and one like beemers of old, that grows on you as miles mount up, it seems.

Overall the bike seemed quite manageable and not too much of an issue moving it around too. Rode in a very 'BMW-like' way, from bikes I remember from the 70's and early 80's! A very pleasant way to travel....

Regards
Mark

Thx for notes and advice. Have had a bit of a play....

• Replaced that hose....it was split both ends and in the middle!
  
• Replaced spark plugs.
  
• Tinkered with the throttle stop screw, it initially wasn't doing anything
  
• A squirt of wd40 on the throttle cable pulley thingy.
  
• Checking/pressing together the connections of the wires from the tank
  
• Checking/connecting in connecting wires on injectors and moving a cable tie as one wire on middle injector seemed strained.
  

Went for a ride and now seem to have about 950rpm tick over and no repeat of stalling.
Will keep an eye on it, but seems promising.
Regards
Mark

Good to hear you got that sorted.