Fuel consumption

[grant71]

Since i bought my K100 it has been very heavy on fuel. CO level about 10. A few days ago i met a young man who used to work on K s. Look for rubber on right top of air chamber. Take no 5  allen key and turn very slowly till the reading is 2.5. Lucky for me there is a carb shop near by. Went there this am met Neil the owner and he inserted probe in the exhaust. 10.5  ! ! I made the adjustments little by little anti clock wise until it reached 2.5. Neil charged me the equivalent of  $ 5 US. Did i have a good day ? Will check my fuel usage this we. Btw. Its a glorious autumn day 1pm and im lying on my bed with my dog Rusty and listening to THE MODERN JAZZ QUARTET playing Summertime. Fellow bikers : life does nt get much better than this.

[WayneDW]

Glad things worked out for you.
I am confused as to what exactly you were adjusting?

[Scott_]

Glad things worked out for you.
I am confused as to what exactly you were adjusting?

I think it's a MAP air flow sensor for controlling exhaust CO concentration. It's only on the jetronic fuel systems that I know of.

[grant71]

Yes. Adjusted the air flow meter. Went for a run today to test the con. 121 km ( 75 mi ) used 9.6 lit ( 2.1 gal  ) which have me 7.94 lit for 100km or 35.7 mpg. Im a bit disappointed. Expected better. Moved along at about 100 km per hour ( 62 mph ). Mostly country roads. Quite a few stops. Any ideas pse

[Grim]

Correct me if I'm wrong but I thought that adjustment was more at base idle.

100's don't have o2 correct? To keep from burning valves I'm sure the fuel map is going to stay on the rich side since there is no mixture feed back.

If the AFM is the same as my truck you can adjust the spring tension on the door. More spring would lean it.

My nasty little 86 4runner on 33in tires strings out 24 hwy. My k1100 is pulling 40 mostly hwy. The O2 sensor giving feed back is the key.

[jetpoweredmonkey]

My K100 gets a consistent 36MPG, and it is in a fine state of tune.  I'm not easy on the throttle but I do keep the bike in excellent shape.  I have seen 40MPG if I am keeping the speed down to 65MPH or less and not in stop and go traffic.  I doubt it will get much better than that under any conditions.

The adjusting screw on the AFM (air flow meter - it's just a gate swinging in the breeze with a potentiometer attached to it) controls how much air bypasses the air "gate".  The screw is mostly in effect at idle but does have an effect throughout the operating range of the AFM.  Since no two AFMs are exactly alike, this is the baseline adjustment to get it in the ballpark for normal operation.  Lacking a CO meter of any kind, I've never messed with mine.

If your idle and off-idle performance is OK, I'd say your bike is probably pretty normal.  I was going to add a smart-ass comment about how at least your old 100 is so much simpler and easier to work on than the 1100, except with the price of gas these days, the fuel savings do add up kind of fast...  :dunno2:

[mjydrafter]

Here's a link to what I think the OP is doing.

http://skylands.ibmwr.org/tom/tech/co-setting.html

Let me know if I wrong? :dunno

[grant71]

Tks for the replies. Maybe im a bit greedy re fuel con. Jet gets 36 mpg. I also ride a honda shadow 1100 and i get 90miles from 8.26 litres. A question about my K100. Runs well but in 1st gear a bit of a flat spot when i open throttle quite a lot. I live on slope of Table Mountain Cape town. Then in 2nd quite a lot of hesitation and jerking. As i stated , only when throttle opened to get up the steep hills. What could the problem be ?

[jetpoweredmonkey]

Grant, what's the elevation in your town?  There is a high altitude jumper plug on your bike.  I believe the manual says it should be plugged in over 4000 or 5000 feet, can't remember offhand now.  If you are at high altitude, you might try plugging in the jumper, still available from the dealer if you need one.  The plug lives behind the left side panel near the fuses.

[grant71]

Cape town is at sea level and my house is say 200 ft above. The hills are steep thats all

[Grim]

Tks for the replies. Maybe im a bit greedy re fuel con. Jet gets 36 mpg. I also ride a honda shadow 1100 and i get 90miles from 8.26 litres. A question about my K100. Runs well but in 1st gear a bit of a flat spot when i open throttle quite a lot. I live on slope of Table Mountain Cape town. Then in 2nd quite a lot of hesitation and jerking. As i stated , only when throttle opened to get up the steep hills. What could the problem be ?

Start with the basics. Meter your plug wires. Learn to read your plugs and chose a good heat range. Make sure the high altitude plug is out.
Check for vacuum leaks. The FI on the bike is very simple but any vacuum leaks are going to cause a run problem. The fuel pressure regulator increase pressure by sensing a drop in manifold vacuum. If you have a vac leak it will cause excessive fuel pressure and consumption.

[argent brick]

Grant, what's the elevation in your town?  There is a high altitude jumper plug on your bike.  I believe the manual says it should be plugged in over 4000 or 5000 feet, can't remember offhand now.  If you are at high altitude, you might try plugging in the jumper, still available from the dealer if you need one.  The plug lives behind the left side panel near the fuses.

Is there any reason that he can't or should not run the jumper at lower elevations? In my mind, it should lower his fuel consumption. Or am I missing something here?

[jetpoweredmonkey]

FYI, I did a 350 mile trip last weekend with a couple of friends.  One of them was on a 150cc scooter and didn't know the way. He could go 60mph, but not up a hill. I spent the whole ride looking in the mirror and rolling off the throttle, but we had a good time. I also found out the old K can hit 50MPG if you can stay off the gas!

[bocutter Ed]

Similar here. Tail gunned an 8 pack of scoots, ranging from 200 to 650 cc, for 260 miles from Toronto to Bala and then back going around Lake Simcoe. First fill at 220 km took 10 L. So: 4.5L/100km; 62mpg (Imp); 52mpg (US).

[K75RT Keith]

Check the caps on the vacuum ports.   If they are cracked and old they may be affecting your mileage.  Mine did

[Glacial]

Just calculated that fixing the leaks in the inlet manifolds and balancing the throttle bodies has gained me an average of 3 mpg (Imperial), based on 5 fuel-ups before the work was done and 5 after. All riding done on the commute to work on rural roads with lots of bends, speed changes and enthusiastic acceleration, so no differences between urban stop/start and highway cruising affecting the results. Actual figures were 49.1 before 51.1 after.

[theblackfella]

Any suggestions on how to adjust the base idle and mixture on my 1989 K100RS 8v, unfortunately I don't have a gas analyser.
I live in Sydney Australia, had the bike since new, done 200000km,i have done the trip to Phillip Island nearly every year since I bought the bike.
I am giving the bike a complete going over for the first time in years, valve clearances etc.
This is the first forum I have been on, so please excuse any Faux Pas.
 

[The Mighty Gryphon]

I think you want to start with balancing the throttle bodies.  There are some threads here that explain the procedure and present some ideas for simple test set ups.  You can use the search function here to find them. 

I have found with my bikes that new plugs, a throttle body balance, and setting the TPS is all it takes to get the idle nice and smooth.  Of course, it goes without saying that all the vacuum lines, throttle body bushings, vacuum caps and crankcase breathers are tight and free from cracks. 

If it's been more than 50,000km since you replaced the air filter you might want to check it and replace if dirty.