Technical causes of poor fuel economy?

So I've purchased a new-to-me bike and the MPG I'm getting by the time my fuel light comes on vs. what the general consensus is online is drastically different. For me when the fuel light comes on, I've gotten about 25MPG, vs. online reports of ~40MPG. I'm not wringing it out, this is just general highway commuting (usually with some stop-and-go thrown in, about 18km per trip), so what technical issues could there be to cause such bad economy?

Another thing that crossed my mind is that the fuel light could simply be coming on early for some reason. The tank is 15.5L, 3L reserve, but my light seems to come on around 10L used. I don't feel like trying to run it empty to see.

Model/year/mileage of bike?

Is the mixture drastically off, are you comparing USG vs Imp G, are the brakes dragging, is the clutch slipping, are filling the tank completely while the bike is vertical, does it have stock sized sprockets?

Go to fuelly.com to get better reports on consumption. Whenever you fill up take a note on the receipt the amount of fuel put in, then on your trip meter record the amount of kms for the fuel put in. Simple math calculate the amount for consumption.

Side note :lots of things affect fuel consumption. Fuelling done by programming the ecu or the overall health of the bike

GreyGhost said:

Model/year/mileage of bike?

Is the mixture drastically off, are you comparing USG vs Imp G, are the brakes dragging, is the clutch slipping, are filling the tank completely while the bike is vertical, does it have stock sized sprockets?

Click to expand...

2004 Ducati 999s mono, ~25000km. Seller said it has full termignoni system on it, but I know there were various sizes made and I don't know which it is but I'm pretty sure it's not just a slipon. Don't know if it has DP ECU, but the fuel reports I'm comparing it to had people using upgraded exhausts. Bike had its regular maintenance done at 24000km.

* I've started filling the bike while vertical since that was the first thought I had
* Not sure about the sprockets, the bike has aftermarket bits here and there so it's possible they're not stock
* Reports are off American forums, should all be USG. I use Fuelly and while there's only a few other 999 bikes on there, mine is the lowest
* It doesn't feel/sound like the brakes are dragging, but I don't have spools for my rear stand yet (and no front stand)
* Clutch feels fine

Interinstingly enough, I just got an identical bike as my old one, but geared lower than stock. My old one was geared higher than stock. Mileage seems to be about the same.

You have to fill to the top (filler tube), then note the litres purchased to fill back to the same point, and the km from the first fill to the last. Then you can compute L/100KM, MPG, etc.

Don't forget - 'online reports of~MPG', if from US riders - their Gallon is 3.8L, not 4.5L as our Imperial Gallon...

Check the obvious stuff: tire pressure too low, brake dragging, chain seizing up, etc. If you don't have a stand yet, get a helper to pivot the bike up on the side stand to lift one wheel at a time off the ground to check for excessive drag.

Check the condition of the air filter. It won't make a large difference on consumption unless it is almost blocked solid ... but it's worth checking.

If someone screwed up during the regular maintenance and got the cam timing wrong, that will cause all sorts of problems - more than just lousy mileage but also hard starting, driveability problems, low power, etc.

Most common cause: Fuel injection mapping that was done without consideration of part-throttle economy (in other words, waaaayyy too bloody rich). Stock ECU mapping isn't always that great ... my stock ZX10R was showing 11:1 air/fuel in top gear at a steady 90 km/h, which is obnoxious. I have no idea why they did it that way but that's what it was. The bike now has a PowerCommander and there is a pretty significant part of the mapping that has 20% - 30% taken out of the fuel delivery.

Beware someone who claims "air/fuel is perfect 13:1 everywhere". Wrong. That's OK for full throttle, but at part throttle (which inherently means the rider is NOT asking for as much power as possible!) 15:1 - 16:1 with slightly advanced ignition timing will give better economy. The disadvantage is that it is trickier to tune on the lean side and it can take a lot of trial and error to get it right, particularly if you are using a PowerCommander, which has lousy resolution for part-throttle operation. And that's why if you go to a shop and get a remap done for a couple hundred bucks, they're going to make it 13:1 (ish) everywhere and NOT give you good part-throttle operation.

I've ridden with quite a few guys with ducatis & their fuel light is the first to come on lol

Other causes might be valve gaps, stuck injectors, air leaks in rubber parts like bushings between TB and air plenum, or TPS reset is needed. I'm not overly familiar with the Ducati's but these are general FI problems.

Unclear - have you actually calculated your consumption (filled, rode until fuel needed again, refilled, calculated), preferably across multiple tanks to see what fuel economy you're getting...or you haven't but "Just don't seem to get very far before the light comes on"?

Post up the calculated L/100K.

PrivatePilot said:

Unclear - have you actually calculated your consumption (filled, rode until fuel needed again, refilled, calculated), preferably across multiple tanks to see what fuel economy you're getting...or you haven't but "Just don't seem to get very far before the light comes on"?

Post up the calculated L/100K.

Click to expand...

http://www.fuelly.com/motorcycle/ducati/999s/2004/derp/437674

That's mine. The latest tank where it gets better was like 100km on the 401

It sounds like there's a whole lot of different areas that could be causing the problem. Any recommendations where to start, or maybe a shop that would be able to work this out (I'm not a wrencher, don't have space for doing it) without breaking my bank?

espro said:

http://www.fuelly.com/motorcycle/ducati/999s/2004/derp/437674

That's mine. The latest tank where it gets better was like 100km on the 401

It sounds like there's a whole lot of different areas that could be causing the problem. Any recommendations where to start, or maybe a shop that would be able to work this out (I'm not a wrencher, don't have space for doing it) without breaking my bank?

Click to expand...

wth? How is your mileage varying between 22 and 33 mpg? Are you filling to the same level every time? Even accounting for your highway run, that seems like too big a swing.

I would check for free spinning wheels first, that is pretty easy if you have a friend to help hold one wheel at a time off the ground. Most of the other causes obviously require more mechanical knowledge/work.

Your range sucks but with a 15.5L tank (minus a 3L reserve) and a rich fuel map you're within the realm of possibility of everything working properly.