As an experiment - I used "super" 98 octane fuel - and my tank range leapt from 160 miles to 182 miles before the red light comes on (tho I never trust the red light - normally when it comes on I have to be careful opening the throttle, or the bike "blips")-. I do ride the bike hard...
Would other members consider this consumption average?. its mostly urban usage in London.- I keep the bike well serviced and have replaced the fuel lines, crankcase breather vent hose, injectors etc.
I suspect I may have to replace the fuel pressure modulator, as cold starting needs a few revs and help with the throttle ( I also recently put on a new throttle sensor indicator - as it had failed).
I also replaced the temp sensor near the radiator - this made a difference.
I plan on cleaning all the electrical connections under the tank and cleaning the airbox etc
Has anyone any useful tips to help fuel economy? I read of others achieving 200 miles per tank while riding enthusiastically.
thanks
Colin

Interesting. I have to do conversions because I don't think in those antiquated imperial units, but 160miles is about 260 kilometres, which I'd consider on the low end of about right for urban riding. 182 miles is about 293 kilometres, and that's very good around town, about right on the highway. I'm currently keeping detailed records of fuel consumption, and it's a bit frighteningly high at the moment but mostly because of the type of commuting riding I'm having to do, and the fantastic roads I get to do half of it on.

My girlfriend's bike, in much better condition than mine, gets the light coming on simultaneously with mine when we ride together, so either mine is fine or they're both the same wrong.

The most interesting thing I've been noticing is that my fuel usage reliably changes with the fuel I put in, but a higher octane fuel is *not* necessarily better!

Needing some revs to start cold does sound like a problem. The coldest I've ever ridden, with frost on the ground, it just needed the idle adjust open full, and didn't need a lot of cranking at all. If you can access a pressure gauge, checking the FPR could be interesting.

Improve fuel consumption? Keep a close eye on your tyre condition and pressures, ride in a tuck, don't overload the bike, check the wheel bearings, keep the fuel system and air filter clean (that all makes the bike better), don't brake for corners (that's more fun) and be gentle on the throttle (that needs discipline).

This is my Fuely tracking record for my K75.

Its consumption is close to a K100 (which is surprising) and I think consumption is a bit high. My expectations for the K75/K100 would be 4.8 - 5.0 l/100km. I'm currently planning a teardown restoration of my K75 so I will be performing the repairs you mentioned in your first post. Using Ethanol-free fuels certainly helps milage. Tire pressure is a major contributor or inhibitor to good milage and keeping the tire pressures to spec helps safety as well.

I have noticed in an unscientific way.... that when I fill up with a supermarket brand of fuel and ride to work and back it costs me the same as it does when I use there premium fuel. So that's a 140 mile round trip.

I travel on 'A' roads and fast 'B'roads to work daily, sticking to speed limits, and return 50MPG. John

I have a short commute of about 12 miles daily but the speeds are pretty low with allot of stop lights. Under normal commuting conditions I get about the same 180 miles on 4 gallons, which is relatively low, but I tend to drag race every stop light and Colorado doesn't carry high octane gas (91 is the best). During the winter they use a "winter mix" with a 10% ethanol content and that kills my mileage even more (160 miles on 4 gallons) When I hit the highway though I have seen as high as 55 mpg. One trip of mostly good twisty mountain roads I got 253 miles before I saw the red light. That was awesome.

Lets compare apples and apples....

Here is my experience:
K75: between 5 and 6 l/100km
K100rt: between 6.5 and 8 l/100km

I rode a lot with my friend who has a 1985 k100rt and we always get exactly the same gas consummation. My brother (1985 k100rt too) get exactly the same mileage. The 3 of us had the opportunity to ride together and compared. No difference!

There are 4 types of K100:
RT 2v, LT 2v, RS 2v, and RS 4v.

The difference between the RT,LT and RS is in the final drive ratio.
The RT has a ratio of 33:11
The RS has a ratio of 31:11
The RS 4v has a ratio of 31:11

The RT has more torque, but the RS has better top speed.
A RT final drive is more appropriate to pull a chair but the gas consummation is higher

CF

I get a pretty constant 6.5-7L/100km. Always have, expect I always will, on my 1984 K100RT. Fuelly Link

A couple of the local guys in the BMW club have '91 model K100RT's, and constantly get 4-5L/100km. It's been explained by the club k100 god that the earlier K's run the L-jetronic ECU's, which fire all four injectors on every fire. The later K's run Motronic ECU's which only fire the actual injector needed, saving a decent amount of fuel. I've always wondered if it's possible to retro-fit the Motronic to save some money

Both Jetronic and Motronic fires all four injectors at the same time.
Both have a common power supply wire, and a common ground wire for the signal.

Inge K. wrote:Both Jetronic and Motronic fires all four injectors at the same time.
Both have a common power supply wire, and a common ground wire for the signal.

Haha, well he isn't quite the god he seems then! I wonder why the newer K's are getting better consumption then? Hrrm!

I have both a Jetronic and Motronic equipped K, the fuel consumption close to equal at both......we got very low speed limits in Norway.....don't go WOT that much.

Regardless of weather it's a K100 or K1100 16v I get about 4.5/100k at a speed of around 110kph.
The K100 8v had the l Jetronic injectoin and all the parts are interchangeable so there should be no difference except for load or speed differences. You are experiencing other problems and it could be that the fuel consumption problems have come to a head.

colin

there are two major "electrical factors or sensors " that contribute to mixture settings ....relative to the early k bike (2 valve )

1> the temperature sensor on the water stub (behind the radiator ) higher resistance = more fuel used

used to enricher the mix until thermostat operation occurs ...etc (=often goes high resistance on the connections to the wiring harness connector and screw termination of the sensor to the stub and bad connection to the under seat efi computer ) deoxit is your friend .

2> the MAF sensor flap springing (which returns a resistance value relative to air flow volume )

read a few guides about this on the usa sites ...and adjustment ...

besides that, plug selection , high tension lead losses, air filter and fuel used can make a vast difference .

quite a few of us down here often get somewhere between 18 to 20 killometers per litre (5.0 -6.0 liters per hundred ) on aged and unadjusted maf machines ...but mainly well maintained bikes with little misses or breakdowns

just adding to the mix of perspectives

hope it helps

Mixed driving with no effort to safe fuel my fuel consumption has been 5,8 - 5,9l / km. Stock K100 86" but some smoothinig done to the... dont know the word, place where the valves are. Engine completely redone 2009 and only about 6000km ago. Bike is nude and has wide handlebars.