Author Topic: '86 K75S mission to accomplish better fuel consumption  (Read 7075 times)

Offline szabgab

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'86 K75S mission to accomplish better fuel consumption
« on: February 24, 2019, 11:22:23 AM »
Guys, I started a new topic as not to completely hijack the thread about tank internal lines...

There are a few quick easy tests you can do. Are the needles parallel in fifth gear? Mine are, we have metric here but I don't think that matters. You might have a non original final drive. Is the speedo accurate?

It seems to me roughly say 6.5lt/100km, looking at that metric  graph, I googled that to 43MPG, maybe my maths is wrong or something.

The final drive ratio is usually stamped on the top, near the swing arm.

I'm thinking, be sure your fuel economy is bad before looking for the cause.

Dave, in my calculation 43 US MPG is 5.4l/100km and 51.5 Imperial MPG

The speedo is actually 5-10% optimistic, so my fuel consumption is even worse, than on paper. We have km here too, so will check 5th gear, next time I am riding the bike. Also will check the final gear ratio...
  • Budapest, Hungary
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Offline szabgab

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #1 on: February 24, 2019, 11:29:44 AM »
I cannot think of any reasons why your plugs look so good with the fuel efficiency you say you are getting.  They should be black and sooty with the amount of fuel you say you are using, certainly not as clean as yours look. 

Are you absolutely sure your trip meter is running properly?  It is driven by a small electric motor that is speed controlled by some electronics and the rear wheel sensor.  I think it is possible that it could be running slow because of drag in the gearing and not registering distance accurately.

I would suggest taking a ride on a motorway with km markers and checking your readings against them.  a minimum 25-30 km trip should tell you if everything is accurate.

You said, my plugs could show a slightly lean condition, and probably that would make the bike running uneconomical too, if I understand this correctly. The whole lunchbox has been replaced in October-November time, the old and the new are showing the same. Also whilst testing for speedo accuracy using a 50Hz soldering iron (where one should see 60.5km/h or so on the speedo) I tested the tripmeter too, in one minute it showed just over a km traveled, so that was exactly right. It could bind from time to time, but so did the old one? Nevertheless, I will test it using your method of driving a longish known distance and check it that way. Other possibilty is dragging rear brake, which would worsen the economy big time, however bike is easy to push (but rear rotor gets hot to the touch after every ride)
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Offline szabgab

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #2 on: February 24, 2019, 11:32:50 AM »
I'll use 5L/100km when on longer out of town rides at 80 to 120 kph. In town is another story. My workshop is 1km away and my clients, groceries, banking, beer, etc are all within a 5km radius. I'll use 7.5L/100km in town.

Yes, basically this is what I fear, maybe a touring bike made to be used WOT for miles on end is just crap in the city. My scooter was brilliant in that sense, but I could not get rid of it quickly enough, it was so soulless. It was a Kymco however and not one of those old-school good looking Italian ones ;)
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Offline szabgab

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #3 on: February 24, 2019, 12:47:22 PM »
Timing is fairly easy to check...

The good news is that when the edges of the cutout in the two parts are aligned, the timing will be at factory specifications. This is the way the timing is set according to the factory manual I have.  All my bikes are timed that way and they run well and get 45-48 MPG.


Gryphon, I have managed to squeeze in some time to check the plate. It looks OK to me, but please have a look. Thank you!

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #4 on: February 24, 2019, 01:43:06 PM »
. . . maybe a touring bike made to be used WOT for miles on end is just crap in the city.
That is more or less accurate, but WOT also lessens fuel economy.

City life will not only lessen the fuel economy of a road bike but is also likely to increase wear on engine components because insufficiently warmed lubrication isn't effective engine or transmission protection. Condensation won't be thoroughly evaporated by exposure to a sufficient duration of engine heat so increased corrosion of vulnerable electrical connectors is also likely if inspection and maintenance is neglected. That can be somewhat mitigated by waterproof connectors.

Piaggio makes attractive and efficient scooters. In Vermont, electrically-powered mountain bikes with rugged frames, sturdy curb/debris resistant tires and protected electronics are making headway among commuters. Zero Motorcyles would also be appealing under city circumstances, but they're still costly and importation into the 16th century is unlikely to lessen that cost. :giggles

When finally you get your moto tuned and cleaned up, somebody will pay a reasonable price for it if it doesn't satisfy your needs.
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #5 on: February 24, 2019, 02:35:38 PM »
Do you buy fuel in litres and is your odo in miles?

It's always a good idea to check the brakes.

Look at your metric graph,  I worked out 6.27lt/100km (I'm using reading glasses,  so check that) That's 45MPG, 37.5 US

I think that's good, in harsh conditions, for an old bike that may do over 200km/hr, at least the k100 can.
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #6 on: February 24, 2019, 03:25:49 PM »
Do you buy fuel in litres and is your odo in miles?

Look at your metric graph,  I worked out 6.27lt/100km (I'm using reading glasses,  so check that) That's 45MPG, 37.5 US

I think that's good, in harsh conditions, for an old bike that may do over 200km/hr, at least the k100 can.

Fuel in litres, odo in kilometres. The graph is a misleading one, as there are only 12 fuel ups, and the first, rather good reading affects the average, but that is not to be counted, as I bought the bike partially fueled up, also there is a very bad 8.2l consumption, I have forgotten to log. But you are probably right, one should ride a bike rather than looking at stats...
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Offline szabgab

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #7 on: February 24, 2019, 03:48:51 PM »

...importation into the 16th century is unlikely to lessen that cost. :giggles

When finally you get your moto tuned and cleaned up, somebody will pay a reasonable price for it if it doesn't satisfy your needs.


Haha, I knew, the 16th century comment of mine will come back haunting me forever :))

For the price I've paid, I could have gotten myself a very nice scoot, like a PCX, that is practically making gas. I had a 400cc Honda from the 80s, which I sold, because I thought a scooter will be better for what I need it for. But there is something about an old bike, like ours, all that old-school lunacy, that is cramped in one makes me always want one. Also prices of K bikes gone up VERY significantly, and I could make nice money on selling this one, but the thought of one of them Starbucks folks turning it into some ungodly retard on two wheels fills me with terror :)
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #8 on: February 24, 2019, 05:16:57 PM »
Experiment a bit, try some other bowsers, try high octane if you're not already. But you're already doing as good as bocutter, he's getting 5lt/100km (56MPG, 47US) on the highway.

How many other bikes can do 200km/hr and 20km/lt? And heaps of torque to boot.
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #9 on: February 24, 2019, 06:40:51 PM »
First of all, the timing is spot on the factory setting. 

Second, WTF is with l/100km?  that's too friggin' hard for my brain to understand.  km/l.  Fill tank, how much does the pump show went in?  What does the tripmeter say you travelled since the last fill? 

Divide km by the l and you have your answer.  Crap, I can do that in my much abused head as I ride away from the station.  Don't even need a calculator or a pencil.

Third, the speedometer reading has nothing to do with the odometer reading.  They operate on two separate electrical mechanisms.  A measured run is the surest way to check the tripmeter.  It sounds like yours is running accurately, but a measured run is the only test  I would trust.

Last, are your spark plugs the correct heat range?  If they are the proper plugs for the bike, I am pretty sure the mixture is correct, and all the engine control devices are working properly.
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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #10 on: February 24, 2019, 09:36:15 PM »
Second, WTF is with l/100km?
It's the European way of calculating. Here's an extract from the BMW K75/K100 2V service manual available at the world famous MOTOBRICK. COM:
Maximum permissible oil consumption rate: 0.151 per 1 00 km.

This method can be found in use all the way back to the 16th century in Hungary.
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #11 on: February 25, 2019, 07:48:52 AM »
It's the European way of calculating. Here's an extract from the BMW K75/K100 2V service manual available at the world famous MOTOBRICK. COM:
Maximum permissible oil consumption rate: 0.151 per 1 00 km.

This method can be found in use all the way back to the 16th century in Hungary.

:D Laitch, no it can't unfortunately. If that would be true, Hungary would have been the leading scientific superpower of the time as metric and SI system was still waiting to be established. Hungarians up to the nineteenth century were using some strange old ways to measure things, funnily enough resembling a lot more the imperial system than metric and divisions weren't decimal either. 

As to why is the 100km/l the ISO standard over here is unknown to me, Gryphon is right about MPG being simpler to calculate, for me this ratio is more natural, but it is because I grew up with it
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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #12 on: February 25, 2019, 07:55:16 AM »
Hungarians up to the nineteenth century were using some strange old ways to measure things, funnily enough resembling a lot more the imperial system than metric and divisions weren't decimal either. 
My mistake—I thought you were a time traveler from the 16th century based on your relationship with your moto. :giggles
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline bocutter Ed

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Re: '86 K75S mission to find out about crap fuel consumption
« Reply #13 on: February 25, 2019, 07:59:30 AM »
Yes, basically this is what I fear, maybe a touring bike made to be used WOT for miles on end is just crap in the city. My scooter was brilliant in that sense, but I could not get rid of it quickly enough, it was so soulless. It was a Kymco however and not one of those old-school good looking Italian ones ;)
On that note I should mention that my ('61 Puch DS60) scoot's mileage drops from summer's 75+ mpg to 50 mpg in the winter.
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #14 on: February 25, 2019, 09:19:03 AM »
First of all, the timing is spot on the factory setting. 

Third, the speedometer reading has nothing to do with the odometer reading.  They operate on two separate electrical mechanisms.  A measured run is the surest way to check the tripmeter.  It sounds like yours is running accurately, but a measured run is the only test  I would trust.

Last, are your spark plugs the correct heat range?  If they are the proper plugs for the bike, I am pretty sure the mixture is correct, and all the engine control devices are working properly.

Gryphon, good to know, HES position is correct. Plugs are Bosch X5DC, so that is factory standard, I believe. Plugs were like this since I have gotten the bike even though I had massive air leaks, ailing fuel pump, semi-clogged fuel filter, spitting injectors, intake valves too tight, air leaks at the exhaust, alternator barely charging (I corrected all of those since), so I guess the FI system is very robust and can hide quite a lot before throwing in the towel...
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #15 on: February 25, 2019, 09:45:52 AM »
At no time during your ownership of this bike has the mixture been on the rich side according to your plugs.  At this point I would take a break from obsessing on l/100k or whatever and patiently wait for the return of warmer weather to check fuel efficiency again. 

Meanwhile, I'll try to shake off the feeling that there is something odd about how the variables are being measured that we aren't seeing.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
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'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #16 on: March 04, 2019, 04:40:14 PM »
OK gents... Weather is starting to clever up, so I have decided to do a 60km round trip to visit a new injector cleaners', everybody is raving about. Odo is spot on down to the last decimal, however given the margin of error of the speedo it should have been 5-10% higher, shouldn't it?

The reason for a new cleaning attempt was, that the first place, I have sent my injectors to to be cleaned was strange, they never really said what was exactly done to my injectors, even though I asked for reports, I have never been given one, so on, so forth. Now I know why, basically they did f. all to them. I will get my money back, otherwise it is small claims court, as they must have only replaced the o rings and soaked the bodies in acetone, or something. This place, I went to today proved, what I feared - the injectors were dirty, internal filter was never replaced and they managed to clean plenty of sandy residue out of my three injectors. They did a proper flow chart, shame they did not do one at the beginning, now they are 147ml, 147ml, 150ml. One of my injectors had to be ultrasonically cleaned three times, as after the first two attempts it was still flowing 1/3rd, what the others did. Unfortunately the spray pattern from that one is not perfect either and the plastic body is cracked, so I will have to source one from somewhere... Ebay ones are most likely not suitable, also I need one, not three or four.
 
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #18 on: March 04, 2019, 10:37:12 PM »
Wow!  Here's hoping that you have found the problem.   It's getting close to riding season.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline Martin

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #19 on: March 05, 2019, 12:32:53 AM »
I had mine cleaned professionally twice but still had a backfiring problem on overrun. I tracked down and fixed all other contributing factors and fixed them. I then built my own cleaning and test rig and after cleaning and getting even flow and patterns no more backfiring. I also had a definite improvement, more get up and go and probably improved fuel consumption.
Regards Martin.
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #20 on: March 05, 2019, 07:57:46 AM »
I got some injectors at the car wreckers for one of my spare bricks which seem OK but have only riden around the block with them. The injector and part number are almost identical. (part no. 0280 150 208) They were from a six cylinder BMW 520i 1983 model. Also a net search suggests many 90's models as suitable. Some having 4 holes which are supposed to be more economical.
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Offline Martin

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #21 on: March 05, 2019, 01:15:56 PM »
 There are alternate views on 4 hole injectors and there are no posted verified performance tests showing any benefit of the 4 hole type.  A mates son who works with injectors said that because of the way they are positioned there would be no benefit. A lot of the seat of pants reports stating that after fitting, I felt a definite improvement would be the same if you cleaned your stock injectors. Cleaned and flow checked my a 150,000 K injectors and felt a definite improvement.The one down side of the four hole injectors is that the holes are a lot smaller and therefore more prone to blocking. Until the one hole versus the four hole is actually dyno tested  objectively without bias and the results printed I'll stick to the stock ones.

Some owners have actually reported increased fuel consumption when switching to the four hole ones. I've had my injectors cleaned, supposedly flowed and pattern checked twice and I never felt any improvement. I decided to build a rig for cleaning checking and flow testing. It took a lot of cleaning to get the flow and patterns right using my rig plus an ultrasonic bath and a injector pulsar. Once I got them right the improvement was immediately felt and was noticeable. If I had just fitted four hole injectors I probably would have said the same. I would love someone to do a dyno test cleaned and pattern checked one hole versus four hole.
Regards Martin.
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #22 on: March 05, 2019, 04:04:48 PM »
http://www.motobrick.com/index.php?topic=5021.0

I have read various threads, where people were suggesting replacement part numbers for injectors of different cars-trucks and others dishing them, as not suitable, so I am a bit confused. Also if you replace only one, would that cause a mismatch with the other two OEM ones? Are K100 injectors the same? Judging by the part numbers, till '89 they were
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #23 on: March 05, 2019, 04:20:30 PM »
There are alternate views on 4 hole injectors and there are no posted verified performance tests showing any benefit of the 4 hole type.  A mates son who works with injectors said that because of the way they are positioned there would be no benefit. A lot of the seat of pants reports stating that after fitting, I felt a definite improvement would be the same if you cleaned your stock injectors. Cleaned and flow checked my a 150,000 K injectors and felt a definite improvement.The one down side of the four hole injectors is that the holes are a lot smaller and therefore more prone to blocking. Until the one hole versus the four hole is actually dyno tested  objectively without bias and the results printed I'll stick to the stock ones.

Some owners have actually reported increased fuel consumption when switching to the four hole ones. I've had my injectors cleaned, supposedly flowed and pattern checked twice and I never felt any improvement. I decided to build a rig for cleaning checking and flow testing. It took a lot of cleaning to get the flow and patterns right using my rig plus an ultrasonic bath and a injector pulsar. Once I got them right the improvement was immediately felt and was noticeable. If I had just fitted four hole injectors I probably would have said the same. I would love someone to do a dyno test cleaned and pattern checked one hole versus four hole.
Regards Martin.

Martin, I have realised it a long time ago, if you want something to be done properly, you have to do it yourself.

To be honest, I did not feel a straight yeahaa after cleaning, but it could be, the dodgy injector was throwing my throttle bodies off-balance, which I corrected a while back, and now the balance is offset again because of a properly working troika of injectors. I will get back to the petrol station, where nobody bothers me, if I am poking around my idling bike with a strange concoction of coloured fluid, tubes and posh fruit juice jars :)

As to the hole-theme, I have never seen a dyno test for the different injectors, I am not sure, why nobody ever bothered with it, as there is a lot of discussion on it.
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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #24 on: March 05, 2019, 04:39:26 PM »
I have never seen a dyno test for the different injectors, I am not sure, why nobody ever bothered with it, as there is a lot of discussion on it.
If you're referring to a lot of discussion about injectors to be used in the classic K models, that's probably because these are road motos rather than race motos, and many would rather be riding when the moto is running smoothly instead of investing fuel dollars on dyno testing.

Be patient. Somebody will come up with the data, but from what you wrote in your previous post, if you want it to be good data, it seems like you'll need to do it yourself.  :yes
  • Along the Ridley in Vermont.
  • 1995 K75 72,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

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