Diminished Fuel Mileage

I agree that there must be some restriction in the system. Air filter sounds like a good start. Also, check to see if something built a nest in the exhaust. Mice can cause all sorts of problems by packing stuff in there.

Other possibilities could be a switch in your area to a higher ethanol blend of fuel. I see a 4 mpg difference in my area between summer and winter blends. Also see differences between fueling up in SE Michigan vs Ohio.


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dc112675 said:

It seems like you are barking up the right tree though with the air filter. I'm curious what they put in (or as you suggested, what they left in). I know a K&N is about 3x as expensive as an oem AF.

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The K&N is reusable if cleaned and treated properly with the oil. I would think that is why they think they are worth more. I have it from other sources, that the OEM filter performs better... Perception being 9/10 of reality, Your mileage may vary.

I am having the same fuel mileage problem. Using premium fuel, new air filter, tire pressure normal, temp at 3 bar, new spark plugs, Honda certified mechanic said valves are fine, brakes do not seem to be dragging, ran 4 bottles of injector cleaner, riding is still the same. Down to 400-430 km per tank now was at 600 km. Have you had any luck in finding the problem?

Ok, here is the update to the bike, I just recently had it serviced by a Honda place, as the place I did have it serviced went bankrupt (As I am finding, this was a good thing)

The Honda mechanic said the air filter was indeed not the correct one and had put in the correct one, cleaned out all the bugs from the air box. He replaced everything as necessary. From there, looked for codes, there is none. Checked the valves, said everything is great.

In fact, he said the engine is in amazing condition.

I only had one chance to run the bike since, and it seemed to be getting perfectly fine mileage, but after the 1/8 of the tank was gone, it started sucking the fuel pretty quickly.

I have gone about 147km, and it had eaten 3/8 of a tank

So, going to bring it back in later this week, or next and see if they can figure anything else out.

I think you need to do the math... figuring mileage based on the gas gauge after 3/8ths tank won't be that accurate..

Fill your tank, ride most a tank full , fill the tank to the same spot and divide the miles driven by the gallons used.

Do this for 2 or 3 tank fulls to get a reasonably accurate mpg/kpl.

Use actual miles run and gallons filled to calculate fuel mileage. "Estimating" it using the fuel gauge will generally be pretty far off.

Were I the recipient of a non itemized receipt like you have, I would go back to the dealer/mechanic and ask what they typically do in said "premium service". And I would write it down on my copy of the receipt - mostly for my own records.

I also would ask what kind of oil they used, what kind of oil filter, etc. In short, you want to know everything that was done to the bike - if only so you know when to repeat one or more of these service items. Make sure the record has date and mileage on it.

Well, hard to get it itemized when it went bankrupt two weeks after I was realizing there is an issue, but whatever, it is too late for that now.

Anyhow, someone in another forum suggested the t-stat is probably failing, that even though it is registering correct temp, it will cause diminished fuel mileage until it outright fails. So maybe that is something to search on....

As for mileage, I do judge by the how much the tank is showing, so far, it seems to be quite exact about amount used. What would the difference be for me to say I only got 150 km on half a tank when normally, I would get 275 km on half a tank, or me saying, I am burning 19.9 km/l?

Because your fuel gauge may not be accurate or even consistent . your earlier post said you were going 600km /tank .

if at that point you were putting on 23 liters, that would be ~ 60mpg . I'm pretty sure no one gets close to that high on a regular basis.

I have to question your method of calculating fuel mileage. I've found some tank to tank variation in the past, and learned to ignore it and just figure out my annual fuel consumption or maybe for one long trip. This is caused by errors filling the tank, different pumps, fuel with and without ethanol, etc. To be honest, though, the variation is at most a few mpg, not the wide swing that you experience.

I'm not disputing your numbers, but you probably should be checking by using only the same pump from the same gas station (try to avoid pumping in diesel fuel) if you continue to check individual tanks. Btw, I noticed that i can squeeze in a few tenths of a gallon after I see the gas first touching the ring at the base of the filler - no doubt due to the surging of the fuel in the tank when I fill it.

Checking the plugs will put to rest the possibility that one coil is weak - but were this the case you would surely feel a drop in power.

My money would be on this problem going away and you never finding the root cause.....

I can only get 500km on a tank and that's riding nice and easy.

Well, unless my odometer is wrong, I would fill it up, reset the trip meters, and run it till nearly empty, which I would get 580 km. I once ran it till I was out of gas which was 593 km. The average was usually 550 km though.

So looking around on the forums of different sites, I think I may have found a few things, One thing suggested was to replace the thermostat, if the bike is not registering proper temp and runs cold, it will consume the fuel (Which, just recently, it was idling horribly. and the temp only showed two bars (Again, this is just very recent, right after the Honda stop) Only 500 rpm until I ride it around for about 20 minutes, then it idles perfect and temp is normal.

Another thing I had found was the ECM unit could also affect it if it fails, but I know it is quite a protected component of the bike, and is mighty expensive to buy! So I pray that is not it.

Warren & Anne said:

One thing suggested was to replace the thermostat, if the bike is not registering proper temp and runs cold, it will consume the fuel (Which, just recently, it was idling horribly. and the temp only showed two bars (Again, this is just very recent, right after the Honda stop)

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Two bars in cooler (< 10?C) weather is pretty classic stuck-open thermostat and will reduce your fuel economy, even in warm weather.

I'll second everyone else's recommendation that you do your mileage calculations based on distance and fuel consumed instead of eyeballing the fuel gauge. The upper fuel tank is not shaped so that the fuel level drops evenly and only Honda knows if the gauge is calibrated to be linear with respect to the amount of fuel in the tank. My own unscientific observations lead me to believe it isn't.

Only 500 rpm until I ride it around for about 20 minutes, then it idles perfect and temp is normal.

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Many years ago I had a similar problem that was intermittent. I cleaned all of the cold idle linkages on the throttle body (and do so any time I have the air box off) and it hasn't happened since.

I doubt the ECM is at fault; usually the parts that die are the circuits that interface the processor with the sensors and you'll get a fault code for that. It is possible that one of the temperature sensors or the MAP sensor is returning plausible-but-wrong values, but those are pretty easy to test.

--Mark

As for me. I am having the same problem as Warren&Anne. I have been keeping a very accurate records on my iPhone using the ?Road Trip? app, which keeps everything from the station to the price and plots it on a graph for you. I have mentioned my problem and fixes I have tried in earlier post.

Ok, figured out the gas mileage, 6 L/100km

I agree with what others have said... calculate your mileage manually through multiple tanks. My suggestion would be 3 to 4 tanks because mileage will definitely vary. Your 6L/100km figure, which converts to 39 mpg, is a bit low but could actually be the result of a slight error in gathering the basic info used to compute the fuel usage. If you consistently see this 6L/100km figure through 3 or 4 tanks, then you can be assured that this is accurate.

Here is how I keep track of my fuel consumption. First off, pay no attention to that blasted fuel consumption figure on the dash screen! The only way to get accurate fuel consumption is to manually compute it yourself.:

1. Fill up your tank to an easily identifiable point in the filler neck EACH time. It's important to be consistent in this. I (consistently) put my bike on the center stand and fill to where the gas level is just touching that little horizontal bar that is on one side of the filler neck. Be sure and get a receipt that shows gas volume put in the tank.

2. Record the bike's mileage on the gas receipt. I do this by scratching the mileage on the receipt with my key.

3. Ride through at least 2/3 of a tank or more (say 200 miles <322 km> minimum) to increase accuracy of the resulting computation.

4. Repeat #1, #2 & #3 through 3 or 4 tanks beyond that initial fill-up where you recorded your first mileage.

5. Enter this information into a spreadsheet. Set the spreadsheet up to compute your fuel consumption from the kilometers and liters you've entered. If you're unfamiliar with spreadsheet computations, we'll help you with the formulas needed.

....Here's a screenshot of part of the spreadsheet I used for the month of March. I've done this for every motorcycle & car I've owned in the last 20 years. I just input the odometer mileage and fuel used at each fill-up and it automatically computes the mpg. In this case I added a column of L/100km figures (in red) that were computed from the mpg numbers. Notice how the consumption #'s can fluctuate, in this case as much as 4 mpg. The variation could be caused by the weather (wind), riding style, or terrain. :




Once you've made reasonably accurate calculations over several tanks, you'll have a feel for what your real fuel consumption is and you'll have a number that you're sure of. At that point, the folks on this forum can help you logically proceed to a solution which might be as simple as running Seafoam though your tank.

Have you changed your oil yet to see if that helps. I'm thinking that the bankrupt shop used the wrong grade. Maybe they used a 20W-50 Harley Davidson grade oil. You said it looks squeaky clean but still, it may be the wrong grade.
Thicker oil will reduce your gas mileage.
Depending on the year of ST's, some use 10W-30 and some use 10W-40.
I'm using 10W-30 in my 2005 now and noticing I'm getting better gas mileage.
Make sure you use motorcycle oil and not automotive oil.
Best of luck finding the culprit.

Also the best mileage I've ever seen on my ST is 517 Km's. Thinking I was running on fumes when I seen the lone gas station in site.
Now I need to make a long distance run with the 10W-30 motorcycle oil in it and see if my mileage improves.

Ok, so the gas mileage I posted is the same for 6 tanks. The mileage is typical.

So, the mechanic tested the t-stat, it checks out good, no errors. He checked out things and said the average fuel mileage for those bikes is about 43 mpg, or roughly 430 km to a tank. Informing him the most I have ever got out of a tank was 580 km to a dead stop nearly knocked him on the floor! So now, I am getting at most about 430 to 450.

So I guess maybe I had a super awesome mileage machine, and now it is settled to the average. *shrugs*

Warren & Anne said:

Ok, so the gas mileage I posted is the same for 6 tanks. The mileage is typical.

So, the mechanic tested the t-stat, it checks out good, no errors. He checked out things and said the average fuel mileage for those bikes is about 43 mpg

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That fits with my average fuel mileage which is just a teeny bit higher at 44 mpg.