Author Topic: '86 K75S mission to accomplish better fuel consumption  (Read 3680 times)

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #50 on: March 13, 2019, 10:32:09 AM »
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Haha Laitch, fair point :)

All is back to normal, I must have turned it off meaning to turn off another thread that is driving me bonkers at times :)
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #51 on: March 13, 2019, 10:33:52 AM »
I think it's important to reverse whatever caused the pipes to turn blue.

Find the cause of the brake disc getting hot,  even when not used. Turn the wheel, is there any binding? Brake pedal fee play correct? Brake lever free play correct? Check also while hot.  Wheel turns freely when disc hot?

Your bike may be over reving. You should have 4000RPM at 100km/h Maybe your clutch is slipping. I suppose you have the right tyre. Do you have 75mm inner clutch cable length at gearbox? Correct free play at lever, adjusted from push rod? If so,  in fifth,  foot hard on brake pedal,  2000RPM, let clutch out; the engine should stall.

Do the test only as a last resort.

Dave - the only thing, I could do to reverse this to source some dirty injectors and run them instead of the freshly cleaned ones :)

Rear rotor I replaced today morning before going on a trip of +/- 15 miles. Needless to say, I forgot to test the brake, so a non operational rear brake surprised me a bit down the road, fortunately in a non-catastrophic situation... Anyway, once I pumped it a bit and lightly dragged the rear brake for a while the pads embedded themselves to the new rotor and brake operation is restored to normal. It appears to me, this rotor + pads combo works better, than the old one, as the rotor is not getting too warm after a ride, also it feels like bike is easier to push around. The old one was an ABS rotor, the 'new' a non-ABS one (I have no ABS installed on this bike), it should not make a difference, but it most likely does (however I will report back after a tankful or so, as we all new, how subjective these things are).

4000RPM is 81-82 km/h on the adjusted speedo. Clutch operation is faultless, cable length, free play all set to factory standard. Clutch is not slipping and I have tried your last resort incidentally yesterday, in rush hour traffic I was coasting towards a hard turn in fifth gear, forgot about it and let go of the clutch whilst already maneuvering into the curve at 5-10MPH. Bike stalled, nearly dropping me off, fortunately I managed to squeeze the clutch, saving the bike and my butt :)
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #52 on: March 13, 2019, 10:34:23 AM »
Personally, I wouldn't get too wrapped up in final drive ratios.  My experience is that they don't affect fuel efficiency that much.  I don't think a dragging brake will reduce efficiency as much as you're experiencing either.  If it was, I would expect the rear end of the bike to be bursting into flame.

Have you checked valve clearances?  I can't recall if you have.  I have to admit that I'm grasping at straws right now.  The only other thing that I can think of is a slow leak.  A leak of 2-3 liters per tankful is unlikely, but possible.  Leakage rate, if that is the problem, would be on the order of 1/2 liter per hour of operation.  If it is coming out the vent hose you may smell and/or see some fuel around the swing arm and final drive following a ride.

Gryphon, when on my 400cc Honda I obsessed about gear ratios, swapped a perfectly good set of chain and cog wheels in order to find out it did not do ANYTHING to my fuel consumption even though it made high speed travel a bit less buzzing (but speeding off from traffic lights a chore). Valve clearances were checked, intake sides were a bit tight, but that was sorted out over the winter. I did have the bike ticking over for extended periods (15-20 minutes at a time) to set throttle bodies balance, etc. There was never any fuel coming out of the overflow pipe, so I guess that is somewhat ruled out. ALso the bike is parked in a narrow corridor so it would reek like a petrol station if I'd have any leaks after a ride :)))
  • Budapest, Hungary
  • K75S 1985 model

Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #53 on: March 13, 2019, 11:12:29 AM »
Keep us posted on how much fuel you are using.  I know I'l be thinking of what could be causing your problem. 

Have a feeling it's going to be a palm to forehead moment when you find it.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue
Current:
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Online Martin

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #54 on: March 13, 2019, 02:07:12 PM »
Check the vacuum hose that supplies the FPR where it goes into the throttle body  for fuel traces.

Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #55 on: March 13, 2019, 04:07:06 PM »
Km on odo? Km genuine? Tyre standard?

Your getting 6.3lt/100km, that's ok.

At 4000 RPM you have 82km/h, I'm thinking you should have 100. Maybe adjust it back to original,  or with a helper driving in front with cruise control at 100, do a check, maybe with a few cars.

If I replaced the injectors on my bike and the headers turned blue,  I would take them straight out again.

Can we see a photo of your bike, has it got a name? Mines bluey,  my k75 is in storage, I can't get to it for a few weeks.
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #56 on: March 13, 2019, 04:42:14 PM »
Km on odo? Km genuine? Tyre standard?

Your getting 6.3lt/100km, that's ok.

At 4000 RPM you have 82km/h, I'm thinking you should have 100. Maybe adjust it back to original,  or with a helper driving in front with cruise control at 100, do a check, maybe with a few cars.

If I replaced the injectors on my bike and the headers turned blue,  I would take them straight out again.

Can we see a photo of your bike, has it got a name? Mines bluey,  my k75 is in storage, I can't get to it for a few weeks.

Hi Dave, unfortunately I am not getting 6.3l/100km, as the fuelly stats are distorted by readings, that are not necessarily correct. Check individual fuel ups, last for example was 6.9l/100km, or 34 US MPG, which is not very good, given the longish distances covered and weather playing ball. Injectors I can not swap, as those were the only ones, I had (apart from the "new" one, I bought as a spare). See picture of the header pipes, they are not indigo blue, but have got a blue tint to them. Plugs read fine and if I am correct, blue tint means too rich mixture, that makes engine colder rather than warmer...

I will attach a pic of the bike, it is not named anything, sometimes out of anger I call it the flying piece of shit, but that's all :)
  • Budapest, Hungary
  • K75S 1985 model

Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #57 on: March 13, 2019, 05:00:35 PM »
It might get better mileage without the steamer trunk attached to the rear cowl. :giggles
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #58 on: March 13, 2019, 05:01:36 PM »
Keep us posted on how much fuel you are using.  I know I'l be thinking of what could be causing your problem. 

Have a feeling it's going to be a palm to forehead moment when you find it.

I hope you are right about that. It should be already here if you ask me :D
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #59 on: March 13, 2019, 05:09:13 PM »
Check the vacuum hose that supplies the FPR where it goes into the throttle body  for fuel traces.

Regards Martin.

Vacuum hose has been replaced within the last half a year with a new item together with fuel hoses, crankcase breather, big elbow, air collector box, rubber bushings, vacuum caps, air filter, fuel filter, fuel pump, tires, driveshaft etc etc etc... I am running out of options I am afraid :) Something is not dandy, that is for sure, I just hope, Gryphon is right and tomorrow or to-tomorrow the latest I will trace it to something very obvious...
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #60 on: March 13, 2019, 05:20:36 PM »
It might get better mileage without the steamer trunk attached to the rear cowl. :giggles

Yeah, I hear you, it is very ugly. Since I have replaced it with an even bigger, uglier and boxier concoction from Givi, an E45. People think, I am a delivery boy or something, however I need to keep my helmet and assorted crap somewhere safe, whilst out and about. I was also lugging the city cases with me for a while till I realised all it is good for to make me wider and to carry even more unnecessary crap, so they stay at home nowadays :)
  • Budapest, Hungary
  • K75S 1985 model

Online Martin

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #61 on: March 13, 2019, 05:58:48 PM »
The diaphragm in the FPR can leak causing fuel to be sucked into the throttle body. Minor leaks can increase fuel consumption a major leak can lead to a hydraulic lock with a possible bent conrod. Pull the hose where it goes into the throttle body and check for fuel.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #62 on: March 13, 2019, 06:02:31 PM »
The diaphragm in the FPR can leak causing fuel to be sucked into the throttle body. Minor leaks can increase fuel consumption a major leak can lead to a hydraulic lock with a possible bent conrod. Pull the hose where it goes into the throttle body and check for fuel.
Regards Martin.

OK, fair enough. I will do that tomorrow... So is it fuel visible sloshing around the throttle bodies straight after bike was running, or fuel coming out of the vacuum hose, whilst bike running?
  • Budapest, Hungary
  • K75S 1985 model

Online Martin

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #63 on: March 13, 2019, 06:30:04 PM »
Coming out of the vacuum hose. Simply put there is diaphragm in the FPR on one side there is fuel on the other side there is a vacuum the diaphragm can deteriorate and weep or leak. See picture.

Regards Martin.
 [ Invalid Attachment ]
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #64 on: March 13, 2019, 09:11:39 PM »
I'm thinking the average fuel economy is more accurate than an individual reading. Do you compare the fuel against the distance that has been travelled or the distance that will be?

If the readings are questionable, maybe your fuel economy is good.
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #65 on: March 13, 2019, 10:42:07 PM »
*
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #66 on: March 13, 2019, 11:00:01 PM »
"... sometimes out of anger I call it the flying piece of shit..."

Rhymes with flying brick, well done.
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline rbm

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #67 on: March 14, 2019, 07:10:41 AM »
Rear rotor I replaced today morning before going on a trip of +/- 15 miles.
Should we assume these were European miles (10 Km) or American miles?
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #68 on: March 14, 2019, 07:41:52 AM »
And "today morning" is a funny European way of saying this morning.
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #69 on: March 14, 2019, 09:20:10 AM »
And "today morning" is a funny European way of saying this morning.

Martin - I let the bike run without the vacuum hose attached, it was dry even after a couple of minutes of idling with the occasional blip of the throttle

Dave, I am not sure, if today morning is grammatically correct... You say it this way in Hungarian :)

Robert, I just divided 24km's by 1.6, so I guess it is nearer to US and UK miles...
  • Budapest, Hungary
  • K75S 1985 model

Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #70 on: March 14, 2019, 03:51:56 PM »
It's OK,  your English is incredibly good,  some things just translate funny,  even more funny in german:
Today;                heute
Morning;            morgen
This morning;   heute morgen
Tomorrow;        morgen
  • Victoria, Australia
  • Current; 1985 bmw k100rt VIN 0090567 ('84 k100RT, 87 k100RT, '89 k100rt, '91k75s, '96 Kawasaki Vulcan 1500) Past; V Star 650, Kawasaki klx250, Yamaha tt250

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #71 on: March 19, 2019, 06:03:23 PM »
If the plugs look good with a nice tan color on the nose, I would wonder if the engine is running cold and not warming to proper operating temperature.  That could be caused by a thermostat that is stuck open and cooling the engine too much in the cool weather. 

OK, we might be up to something. I have parts of the fairing in for repaint so I have decided to take the thermostat out, remove the radiator to check for dirt in the cooling matrix, etc. It turns out, the thermostat u-gasket, that wraps around the thermostat body is brittle with age, it is cracked in one place in fact. Somebody has been already at it sealing it with black RTV, needless to say with not much success, as parts of RTV were stuck in the springs looking like seaweed. I just really hope, there is not RTV circulating in the system eventually blocking coolant flow.

Anyway, I tested the thermostat, and it opens and closes as it should, so I cleaned the old gasket and thermostat body and reinstalled it, hoping there will not be much of coolant passage around the faulty gasket. As I have refilled the system it also filled the radiator audibly, so I guess the faulty gasket is not sealing at all, or it does so very little.

I did try to research into a suitable u gasket, as there is no BMW reference number for it, but I did not succeed. Anybody has got any idea, what fits?

Thanks!
  • Budapest, Hungary
  • K75S 1985 model

Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #72 on: March 19, 2019, 10:53:14 PM »
As I have refilled the system it also filled the radiator audibly, so I guess the faulty gasket is not sealing at all, or it does so very little.
<translate on>Yo Bro! I fill the rad with fluid and it made a nice gurgling sound as it filled up. Probably means the passages are clear. Dog, gonna take a chance the RTV stuff didn't mess up my rad.<translate off>
Please turn it back on, and leave it on. :giggles
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #73 on: March 20, 2019, 02:50:44 PM »
Please turn it back on, and leave it on. :giggles

Laitch,  before I first started the engine,  I went to check ,  if the gurgling sound is indeed the system filling with coolant or the radiator did too.  I have undone the radiator hose and coolant trickled out,  so I guess that shows,  the thermostat is not doing what it supposed to, e. g.  keeping coolant from the radiator till proper operating temperature. Also trying to follow Haynes' procedure of letting the engine tick over,  till the thermostat opens and fluid level drops in the filler neck I let the bike idle for 15 minutes,  but the coolant level remained just the same.  After a longish city ride I have checked again,  fluid level is the same....
  • Budapest, Hungary
  • K75S 1985 model

Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #74 on: March 20, 2019, 03:24:48 PM »
Laitch,  before I first started the engine,  I went to check ,  if the gurgling sound. . . .
I was referring to the <translate> function. :giggles I don't think there's anything wrong with your engine other than it hasn't been run enough. Let us know how it's doing after 5000 miles of riding.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

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