Fast decreasing gas mileage

I'm not sure if there is an explanation for what I've experienced, but I am going to put it out there to see what you guys think.

I bought my 02 with 22k on it about a month and a half ago. It seemed to get around 40-42mpg for the first two tanks. About then I changed the oil and tightened the chain. Had the chain tightened while I got new tires, and the guys at the shop told me that I needed a new chain because they had adjusted it as far as it would go, indicating that I needed a new chain.

Since the chain adjustment I have only been getting about 150 miles before the my last fuel bar starts blinking. Haven't tried waiting until I thought I would run out, I just get gas when it starts blinking. Unfortunately I haven't paid much attention to how much gas I put in by looking at the pump, but I'm guessing that I'm only getting about 30mpg now.

I have to be honest, I have become much more comfortable on the bike, and have been riding it more and harder (try to keep it in the vtec range while in the mountains, where I ride it most). I know that my riding habits must have an effect on the mileage I get, but I feel that this amount of change is extreme. I am waiting until I have a reason to make a longer trip across some slab to see how the mileage on highway changed. Anyway I am worried that something may be wrong. Much of the tank I'm burning through now has been riding with my wife (on her own bike) so I have been riding easier, but still experiencing sh**ty mileage.

Temps seem to be fine so I don't think that my tstat is broke. It has not yet had the valve maintenance (saving up for that), but I don't know if that could create such an abrupt change, it literally seemed to get worse overnight (previous owner was a yoga instructor though...). I checked the chain tension, and it looks good as well. Vtec kicks in at normal rpm range. Don't know what else to look in to.

Is there any chance that a faulty chain adjustment could have thrown rear wheel alignment out of whack and decreased mileage, or do you all have any other ideas as to what could change mileage so much and so quickly?

 

Slick-50...

 

I no longer have my 6th gen shop manual, but I would suspect one of the F/I sensors. A chain would have to pretty tight to influence MPG that much. You could try pulling in the clutch at about 40-50 MPH and seeing how quickly the bike slows down, just to see if there is something amiss with the brakes or wheel bearings.

From what I recall, the '07 got right about 42 MPG unless I was enthusiastic, and would get as little as 32.

 

As said, why guess about mileage, calculate it. The way you ride your bike is the biggest thing that will change the fuel consumption. I doubt if changing tires adjusting chain have affected things, but who knows.

What drove me initially to doing my own maintenance is seeing sloppy work being done at shops.

 

Third call for actually measuring your mileage so you can know what you are really dealing with here.

Also, unfortunately these bikes don't get as great mileage as you would hope.

 

You're right. Take me out of school for a couple weeks and I get all lazy on the details. These last two tanks are the first that I didn't calculate, mostly because I didn't want to see how big the difference would be. However, I always reset the tripmeter when I get gas, so it will be easy enough. I will do a couple tests, one with a solid trip of floggin her around through the hills, then calculate, then another with a ride to boulder on mostly highway (that will be my summer commute when my internship starts up) round trip, calculating again afterwards.

Maybe the difference isn't a much as I though. One other thing I though about is that when I first got her I was riding in pretty cool weather, and lately it has been getting pretty effing hot, that might do it too.

Tink- Yeah I love her and she is doing me right, hope we ride together again soon

 

Financially, maybe, only if you don't factor in the lower insurance and trips to a psychiatrist you avoid by having a fun, sexy machine like my Mags (thats what I decided to name her) to keep you smiling. That and most of us NEED speed, and you would have to spend a sh*t ton of money on a car to get the speed you get with a bike.

The maintenance aspect of a bike is a bit of a headache though. If I had the resources, I would drive a Ferrari and have the speed and the sexy in a slightly safer vehicle. Probably just as much maintenance though.

 

This is less of a ride style issue and more of a stuck thermostat issue. I know you say that your temps are fine but what are you considering "fine"? I had the exact same problem last year and my temps seemed "fine" to me as well. The bike should run at a minimum of 168-172F even in below freezing temperatures. The service manual specifies that the thermostat should begin to open between 176F-183F and be fully open at 203F. Anything less will cause the FI system to dump fuel in the cylinders in an attempt to warm the engine to optimal operating temperatures for emission control reasons.

Even being stuck open the slightest will cause problems. Monitor your temps and if you go on the highway for 10 minutes at just 60MPH you will be able to tell. If you're even below 168F... your thermostat is stuck at least somewhat.

FWIW... I consider myself fully modified as far as the engine, fuel system, and exhaust go with a full exhaust, no pair valves, no flapper, no snorkel, no evap can, power commander, no 02 sensors, and a custom tune. Since then I have NEVER seen my MPG drop below 36MPG even when flogging the shit out of the bike and running between 90-120MPH for extended periods or lots of twisties and rapid acceleration at continuous high RPMs. The only time that I experienced shitty gas mileage was the stuck thermostat and it took me a while to track it down.

 

best bet ride it in the morning when the air temp is not so high.
the bike should be over 168 degrees if it doesnt go over 160 the t stat is stuck open, I just did mine.

 

Let me add that if it is your thermostat get it changed asap or you'll be chainging fouled plugs as well.

When I bought my '02 with 21k miles on it it was getting 23 miles per gallon. I have no idea how long it had been getting that mileage and the previous owner thought it was just the way he rode. Anyway, I changed the thermostat and it got up to 29mpg, maybe 30 if I ran a whole tank out on the interstate. I finally got aroudn to changing the spark plugs and all four were fouled. Once they were changed I get around 40 on the interstate and around 33 city/mixed.

Also with the plug change came new found power that was lost with the bad plugs.

10 more MPG and front wheel lifting power that previously wasn't there... can't ask for much more.

 

For economy I seldom do as well with my road bikes as with my 86 jetta TD. It gets me 49 mpg loaded with a 800 pounds of cargo. I have snow tires on all 4 wheels but havent needed them lately.

 

I have managed to squeeze 47mpg out of my 99. 217 miles on one tank. Most of that was interstate cruising at 70 being as gentle as I could with the throttle. 70 miles or so of it was 55mph two laner with a few twisty bits, still watching my wrist as I was trying to make my trip in one tank. I gassed up ten miles from my destination cause I chickened out, low fuel light had been blinking for at least fifteen miles. Still had 3/4 of a gallon in it. I was unaware of it but the thermostat had been bad at this time, I just thought the bike took a long time to warm up. It was in the 80's that day so the bike ran at proper temp. As soon as the temperature dropped the bike began running around 145-150 and gas mileage began to suffer. I actually put a piece of cardboard over the inside of the right radiator for the last month or so of the riding season in PA last year. Sucker actually ran at perfect temp in 45-55 degree weather that way...

 

I really don't think its the tstat. the bike warms up to above 170 just fine and when I ride in warm weather it goes up to around 203-209 at stop lights, and will hover around 190 when moving. I do wonder about the plugs though... How hard are they to change out? I will check my service manual, but any first hand experience is good too.

Thanks for all of the input so far guys, I will get some calculations soon and check my plugs when I get a chance.

 

Have u wash n clean ur carbs or throttle bodies? Normally low mpg is symptom or needing them to be washed n cleaned. When was e last time it was done?

Also keeping e revs in e vtec zone is like a leaking gas tank.

Sent from my Desire HD using Tapatalk

 

Try this http://www.fuelly.com/
I use it every time i fill up, no need to guess at all....you might be suprised !

 

keep in mind too, besides different riding conditions greatly affecting mileage, to try to calculate off individual tankfuls is tough on any vehicle, but especially a bike. The tank may not be as "full" each time. So say one time you fill it up you have say 4.8 gallons overall and then the next time you fill it up you have say 5.0 gallons overall. 2/10's of a gallon aren't a whole lot, but if you calculate for one tank it can have a big effect on the apparent mileage. The more tanks you average over the less this matters.