Author Topic: '86 K75S mission to accomplish better fuel consumption  (Read 9347 times)

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #75 on: March 20, 2019, 06:05:59 PM »
The thermostat doesn't stop coolant entering the radiator, it stops circulation while cold. The level didn't drop because you filled it properly and slowly, so there were no trapped air pockets.

There may or may not be a loose toggle "thingo" on the thermostat, position it uppermost so that air bubbles can pass through allowing the system to self bleed. Keep looking and you will find a supplier for parts, it's good to find one close-by.

The thing that would worry me is the injectors,  check the part number and how much fuel they flow. Check the accuracy of the speedo and the other suggestions that aren't verified yet.

Dave, thanks for your answer. The injectors are factory standard as discussed before, flowing 150,147,147ml or thereabouts. Speedo and tripmeter are again very accurate. Haynes states to fill the system with coolant and wait till the engine reaches operating temperature, hence opening the thermostat. When this happens, radiator is filled with coolant and you should top up. As I understand this, thermostat is closed till 82 or so degrees Centigrade, so if you fill the system with cold coolant, it should not fill the radiator?
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #76 on: March 20, 2019, 06:11:31 PM »
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.

Laitch, if I do not have an engine operating at correct temperature, because the thermostat is leaking into the radiator I can seriously f*ck up the engine in less than 5000 miles. So I better keep looking for solutions (minus replacing an otherwise perfectly working thermostat with an expensive new part, because I could not source a 1$ piece of rubber) :)
  • Budapest, Hungary
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #77 on: March 20, 2019, 06:34:14 PM »
Your filler neck goes straight into your radiator, the thermostat can't stop that,  it only stops radiator  circulation while cold. Have a closer look at the other suggestions too.
  • Victoria, Australia
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Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #78 on: March 20, 2019, 06:36:36 PM »
Laitch, if I do not have an engine operating at correct temperature, because the thermostat is leaking into the radiator I can seriously f*ck up the engine in less than 5000 miles. So I better keep looking for solutions (minus replacing an otherwise perfectly working thermostat with an expensive new part, because I could not source a 1$ piece of rubber) :)
How much do you believe that thermostat is leaking? Have you taken the temperature of the coolant when it should be warmed up and discovered it is drastically cooler than it should be?

If you're serious about protecting the engine because the thermostat is leaking, you'll buy the correct thermostat or try what has been suggested and used by others already instead of trying to cobble together something. The K engine is a precision machine so it shouldn't be treated like a donkey cart or Lada.. :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.
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #79 on: March 20, 2019, 07:45:53 PM »
You said you had access to k100 injectors with a lower flow rate,  then you said you replaced the injectors,  then your headers turned blue. Running lean will cause overheating, make your headers turn blue and finally could cause your valves and seats to burn out. Get injectors that suit your 2V k75, not injectors that suit a 4V k100. A supplier may sell you something that they say suits your bike,  but sometimes it pays to check the part number to be sure.

Either your bike is over reving or your speedo is out, or both.

It's probably better to put stuff back to original.
  • Victoria, Australia
  • Current;'86 K100RT Past; '97 Yamaha V Star 650 Yamaha V Star

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #80 on: March 21, 2019, 03:59:47 AM »
How much do you believe that thermostat is leaking? Have you taken the temperature of the coolant when it should be warmed up and discovered it is drastically cooler than it should be?

I do not know. However I thought a radiator, that is not staying empty till operating temperature is reached was a good enough indicator. Looking at the radiator itself and not schematics I see, that the filler tube is directly connected to the rad, so I am not sure, what Haynes is on about...

If you're serious about protecting the engine because the thermostat is leaking, you'll buy the correct thermostat or try what has been suggested and used by others already instead of trying to cobble together something. The K engine is a precision machine so it shouldn't be treated like a donkey cart or Lada.. :giggles

OK, so following your cobbling together logic, I should replace whole assemblies, because of faulty parts, new injectors because O-rings are leaking, or a new engine, because of a failed main shaft seal?
  • Budapest, Hungary
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #81 on: March 21, 2019, 04:07:44 AM »
You said you had access to k100 injectors with a lower flow rate,  then you said you replaced the injectors,  then your headers turned blue. Running lean will cause overheating, make your headers turn blue and finally could cause your valves and seats to burn out. Get injectors that suit your 2V k75, not injectors that suit a 4V k100. A supplier may sell you something that they say suits your bike,  but sometimes it pays to check the part number to be sure.

Either your bike is over reving or your speedo is out, or both.

It's probably better to put stuff back to original.

Dave, there is some misunderstanding here. I have never said, I have access to K100 injectors, we were merely discussing the difference between 2V and 4V injectors. My injectors are the original ones, they have been cleaned and flow tested. My pipes turned blue-ish afterwards, however since posting the photos of it, I have been told, they are well within range, so I was worrying about nothing (as usual). As to why the difference in the gauge needles is unknown to me, the cluster is off a police version of a K75RT and it could have had a different ratio, however the tripmeter and speedo are very precise.
  • Budapest, Hungary
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #82 on: March 21, 2019, 08:26:34 AM »
OK so it sounds like you took the injectors out,  had them cleaned and put them back in. That doesn't always mean they are original with the part number 0280150210.

Check the part number!

A previous owner may have changed them,  but more so I'm losing confidence in the guy you payed to clean them, especially  if he was the one that said they're OK.  Maybe he just gave you some OK second hand ones, which explains why they turned blue. It's only a consideration at this point. Check if they have one hole or four.

Find out if you speedo is wrong or your tacho, or,  if they're good, your bike is over reving, reducing fuel economy.

If there are any trapped air bubbles in the radiator while filling the coolant, they can't escape until it starts circulating. This happens after the thermostat opens,  so then requires topping up,  I think this is the point made by Haynes.
  • Victoria, Australia
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #83 on: March 21, 2019, 08:44:34 AM »
Find out if you speedo is wrong or your tacho, or,  if they're good, your bike is over reving, reducing fuel economy.

If there are any trapped air bubbles while filling the coolant, they can't escape until it starts circulating. This happens after the thermostat opens,  so then requires topping up,  I think this is the point made by Haynes.

Daveson, he did some measured runs a couple weeks ago, and the odometer checked out perfect.  As far as Haynes, from past experience, I wouldn't trust anything in that manual unless I read it somewhere else.

Regarding the thermostat, as long as it is opening and CLOSING properly, I wouldn't be too concerned about it.  The reason I mentioned the thermostat earlier was that if it was stuck open in cold weather the engine would have a tendency to run a bit rich.  The plug readings and the successful test confirmed that it was operating properly.
  • 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 Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #84 on: March 21, 2019, 08:51:03 AM »
. . . I thought a radiator, that is not staying empty till operating temperature is reached was a good enough indicator.
A good enough indicator of what? This statement might indicate a translation problem.

The radiator shouldn't be empty, regardless of whether the engine's operating temperature has been reached. It should be filled with lower temperature coolant that isn't circulating until necessary. When the thermostat opens, hot coolant displaces the existing coolant and enters the radiator to be cooled by circulation through the radiator. The displaced radiator coolant—that is already at a lower temperature—enters the engine to immediately begin lowering the engine temperature by absorbing heat. To repair systems effectively, it's helpful to learn how they operate.

When a cooling system is recharged with replacement coolant, the system is filled with the thermostat open, which means coolant fills the radiator, the hoses and the engine water jackets. When the main system is filled and purged of air, the radiator is capped then coolant is added to the reservoir to reach a level between the Max and Min levels marked on the reservoir.

It isn't unusual for instructions to be misunderstood. One impediment in your case is an occasional language barrier. I use three manuals and cross-reference them for instructions when one of them seems unclear to me.

. . . I should replace whole assemblies, because of faulty parts, new injectors because O-rings are leaking, or a new engine, because of a failed main shaft seal?
Injector o-rings, shaft o-rings and seals were designed to be replaced. The thermostat o-ring wasn't. Those are significant differences that seem to elude your understanding. Our motos' thermostat o-rings differ because they clasp the perimeter of a thermostat's flange. Somewhere somebody might have replaced that o-ring using a different o-ring, silicone sealant, superglue, some effort, some patience and experimentation because they understood how the system worked, needed to get it done and didn't have the luxury of spare time for theorizing. If their effort creating an OEM o-ring substitute has been successful, I haven't yet found it on the Internet. They might just be out riding instead of writing.

Substitute thermostats have been tried and have been described on this site. Only your personal effort at experimentation will determine what is possible within your situation.
  • 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 daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #85 on: March 21, 2019, 09:07:19 AM »
Hi Gryph, yep his odometer seems good,  but at 4000RPM he is doing 82km/h, I'm thinking he should be doing 100km/h. Something is wrong somewhere. I can't get to my k75 for a while,  to verify this. Hopefully someone can chime in.
  • Victoria, Australia
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Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #86 on: March 21, 2019, 10:28:45 AM »
When it comes to estimating appropriate speed for each gear, it's probably best to rely on information provided by a technician experienced with these motos.

Here's Anton Largiader's interactive table where the final drive ratio can be chosen, then in the lower section a performance graph for the chosen ratio can be accessed .
  • 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 szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #87 on: March 21, 2019, 12:40:22 PM »
A good enough indicator of what? This statement might indicate a translation problem.

The radiator shouldn't be empty, regardless of whether the engine's operating temperature has been reached.

When a cooling system is recharged with replacement coolant, the system is filled with the thermostat open, which means coolant fills the radiator, the hoses and the engine water jackets. When the main system is filled and purged of air, the radiator is capped then coolant is added to the reservoir to reach a level between the Max and Min levels marked on the reservoir.


Laitch, water cooling is new territory to me, but as you might have already noticed I am happy to learn about new things, so thanks for clarification. I do try to cross-reference, but in this case Clymers was very vague about the refilling procedure. What Haynes writes in these very words is this: "Start the engine and allow it to idle until it has warmed up to normal operating temperature (...) As soon as thermostat opens, revealed by the sudden steady flow of coolant across the radiator and by a warm top hose, the level will drop again and more air will be expelled in the form of bubbles" Now since I have had none of that, no sudden rush of coolant or levels of fluid dropping I assumed the thermostat does not do, what it supposed to. I have a 'properly' operating engine with shite fuel consumption, so something must be astray. All I am trying to do is to find the cause.


Injector o-rings, shaft o-rings and seals were designed to be replaced. The thermostat o-ring wasn't. Those are significant differences that seem to elude your understanding. Our motos' thermostat o-rings differ because they clasp the perimeter of a thermostat's flange. Somewhere somebody might have replaced that o-ring using a different o-ring, silicone sealant, superglue, some effort, some patience and experimentation because they understood how the system worked, needed to get it done and didn't have the luxury of spare time for theorizing. If their effort creating an OEM o-ring substitute has been successful, I haven't yet found it on the Internet. They might just be out riding instead of writing.

Yeah, probably. however sites like K100 (http://www.k100-forum.com/t7589-thermostat-gasket-not-o-ring), has got various discussion on the theme. I guess, people try not to get futtbucked by BMW telling them not having simple spare parts, when there should be some. After all, you can buy the U-gaskets to a large quantity of thermostats, so most likely there is one to this one too, unless this thermostat is one of those very special BMW issue ones...
  • Budapest, Hungary
  • K75S 1985 model

Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #88 on: March 21, 2019, 01:03:18 PM »
As far as Haynes, from past experience, I wouldn't trust anything in that manual unless I read it somewhere else.

Regarding the thermostat, as long as it is opening and CLOSING properly, I wouldn't be too concerned about it.  The reason I mentioned the thermostat earlier was that if it was stuck open in cold weather the engine would have a tendency to run a bit rich.  The plug readings and the successful test confirmed that it was operating properly.

Oh OK Gryph, thanks! I am hanging on to those very straws you guys are suggesting as my consumption is just as crappy as before... Clymers looks to be a better workshop book, however at times I end up using the Haynes, as it is what I used every time in the past and I keep forgetting, we are pampered with a broad selection of publications for these bikes
  • Budapest, Hungary
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Offline Laitch

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #89 on: March 21, 2019, 05:39:09 PM »
I assumed . . .
Don't assume, verify. It takes knowledge and understanding to assume and, even then, it can be a trap. You don't know if your engine is running cold. You don't know if the thermostat is stuck open. If your moto's engine is cold and if the radiator is filled up to the base of the filler and the air in the system has been purged, then leave the radiator cap off and start your engine. If the coolant isn't swirling, the thermostat is closed; when the coolant starts swirling, the thermostat is open. The swirling is caused by the water pump pushing coolant through the system. At that point, you could measure the temp of the coolant and put the result in your diary. How long this process will take can vary. Give it 15 minutes anyway. This is what was done in ancient times in the land of the rotary dial.

You have many alternatives.  If you removed the thermostat, dropped it in water, heated the water with a thermometer in it and discovered that it both opened and closed fully at approximately the correct temperature, you could reinstall it and try to seal it with one of the ways about which you have read, and live with what you've got. You could make yourself a gasket. You seem to think it will only cost a dollar or so. You could install one of the alternative T-stats mentioned. You can buy a new OEM. You could always temporarily wire a temperature gauge attach to a sensor installed to the water pump to assess things but that is yet more expense. There comes a time for stepping up and actually doing something—that is, once the condition needing treatment has been verified. This might be the time for you. It's scary, I know.

I don't see any payoff for complaining about the lack of an OEM part you think the manufacturer should be supplying you. That ship has sailed.

Like I, and others, stated ages ago in this convoluted thread, engines within vehicles in good shape can experience  ±15% drop in fuel economy during cold weather or stop-and-go driving. Gryph's moto has been well-ridden and well-maintained. It's inappropriate to use his or any moto owned by an experienced, long distance K rider for comparison. The jury is still out on whether the arithmetic concerning your fuel economy is being done correctly, even with all the help you're getting with it from Down Under. :giggles  I think your formerly-neglected relic needs a thorough and extended running-in before fuel economy will change and it will always be lower when riding in the city.

. . . as you might have already noticed I am happy to learn about new things, so thanks for clarification.
I hadn't noticed that. Your happiness has eluded me until now.
 :yippee:
  • 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 szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #90 on: April 09, 2019, 03:47:47 AM »
OK, the quest is still on unfortunately as my fuel  consumption does not want to go any lower -  on an A road doing a constant 60-70 MPH for a fullish tank I was getting 5.9 litres,  which is still way too high.  Compression tester arrived from China,  compression reads good,  but please have a look at the pictures.  Plugs just as nice tan coloured as before,  checked valve clearance again for good measure,  and they are well within spec,  as they have been serviced probably 500 miles ago. What else is there to try?
  • Budapest, Hungary
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #91 on: April 09, 2019, 08:21:01 AM »
Compression looks very good, but then, brick rings seem to last forever.  The tan spark plugs say the mixture is spot on.  I wonder what the plugs look like if you take a reading before the engine warms up.  Possibly, you have an extremely rich mixture in the cold engine.  Is there a lot of soot at the exhaust outlet?

Can you smell raw fuel when the engine runs?  The only thing left is a very small fuel leak when the engine is running.  A leak on the order of 600ml per hour could evaporate in the heat and airflow of a moving bike, but it would still be very aromatic.  Check the top o-rings on the injectors and all the hose clamps on the external fuel lines.
  • 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 daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #92 on: April 09, 2019, 08:32:16 AM »
So is that 5.9 litres per 100km? What number do you want to get it down to?
  • Victoria, Australia
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Offline alabrew

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #93 on: April 09, 2019, 12:20:10 PM »
As it warms up here in the Beautiful State of Alabama, I am seeing my RS 4v gas mileage creep back up to 45 mpg from the 40 I was getting during the winter... ~ a 10% difference. No in town riding for me, about half of my 30 mile commute is 45 mph country roads and the other half is Interstate. That bike is all about acceleration. Gee, I LOVE that on ramp at the airport! I would most certainly lose my license for 12 weeks (or more!). BTW, PO seems to have turned off the red line fuel shut off and I have been into the 10,000 rpm range, so no, I’m not babying it...
  • Alabama
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1979 R65
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #94 on: April 09, 2019, 01:33:00 PM »
Wow,  what speed did you get to on your test track?

Anyway,  hi Gabe, I promised myself not to ask this question again,  but non original injectors can affect fuel economy, did you eventually check that part number? And the number of holes?
  • Victoria, Australia
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Offline alabrew

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #95 on: April 09, 2019, 01:42:36 PM »
What are you? A cop? =-}
Normally, not much over 100 mph (2nd - 3rd gears) and blend into traffic and set the cruise at about 80.
How many weeks suspension at 30 mph over?
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Offline daveson

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #96 on: April 09, 2019, 01:57:54 PM »
Your safe on a test track,  but I'm curious what the law is in USA, in Australia it varies depending which state your in. But Victoria is at least the best state in Australia for historic rego laws. Only one week left and I get my license back. :sip:
  • Victoria, Australia
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Offline szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #97 on: April 09, 2019, 03:08:03 PM »
Compression looks very good, but then, brick rings seem to last forever.  The tan spark plugs say the mixture is spot on.  I wonder what the plugs look like if you take a reading before the engine warms up.  Possibly, you have an extremely rich mixture in the cold engine.  Is there a lot of soot at the exhaust outlet?

Can you smell raw fuel when the engine runs?  The only thing left is a very small fuel leak when the engine is running.  A leak on the order of 600ml per hour could evaporate in the heat and airflow of a moving bike, but it would still be very aromatic.  Check the top o-rings on the injectors and all the hose clamps on the external fuel lines.

Gryphon, thanks for your reply. Over-rich mixture is a possibility, even though the bike does not smoke even on start-ups, tailpipe is somewhat sooty, but not overly so, looks perfectly OK to me. The external fuel lines have been replaced together with some new stainless steel fuel hose clamps. O-rings on injectors have been replaced too, when the injectors were cleaned. The bike does not smell like raw fuel at any time, but I will give it a very thorough once over to check every connection.

I did check the air/fuel mixture adjustment on the MAF, if I have read this correctly, the screw should be out by 4 turns, mine is out 2 and 3/4, so that would indicate a rich mixture compared to factory standard... However plugs reading just perfect somehow throws that out of the equiation... 
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Offline The Mighty Gryphon

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #98 on: April 09, 2019, 03:17:34 PM »
I guess we will have to wait for warmer weather now to see if air temperature/density is causing high consumption.  At 5.9 liters/100km you are within 10% of optimum fuel efficiency.
  • 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 szabgab

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Re: '86 K75S mission to accomplish better fuel consumption
« Reply #99 on: April 09, 2019, 03:39:09 PM »
Gabe, I promised myself not to ask this question again,  but non original injectors can affect fuel economy, did you eventually check that part number? And the number of holes?

So is that 5.9 litres per 100km? What number do you want to get it down to?


Hi Dave, you are OK to ask that, as I never clearly stated, what's what on the injector front :) Injectors are factory standard ones, one hole, correct part number.

As to the consumption, doing 90KMH (I made a mistake before, as that is more, like 55MPH) in 20-22 degrees Celsius on a long stretch of +/- 200 km is just as ideal a scenario as it will get I guess. Users report 4-4.5 l/100km in those circumstances, I traveled solo and I am 75 kilograms, so I was expecting more like 5 or so litres/100km. After all Alabrew doing his stunts and is getting 45MPG on a K100, which is something like 5.2litres/100km, so I guess it is not unreasonable to expect better than 39.8MPG on a K75 in ideal driving conditions... But again, I might be nitpicking (as always) :D
  • Budapest, Hungary
  • K75S 1985 model

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