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 Hey! Where did my mileage go?

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Jäger
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PostSubject: Hey! Where did my mileage go?   Thu Oct 21, 2010 5:15 am

Just did a nice little day trip (writeup and pics to follow). Was sitting here cleaning gas receipts and whatnot out of my pockets. Took another look... WTF?

In the space of a few trips, I've gone from about 73 mpg to about 62 mpg. In about... oh... 400 miles. Three tanks, all equally dismal mileage (for me). Same kind of riding, same terrain.

Well, I'm here and the bike is back there, so I can't even go look at it while I scratch my head. And now that I think of it, it seems to be a bit down in power on the highway. But that might be the equivalent of White Coat Hypertension now that I know the mileage is way down...

Ideas?

My WR is stock, so no mods to wonder about.

I can't check the air filter right now, but it was recently cleaned and the roads haven't been dusty around here in a long time.

Fuel is from the same place, a high volume gas station.

Riding terrain is about the same.

No funny squeaks, rattles,...

This is going to bug me until I get back home.
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greer




PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 5:57 am

I'd bug me, too. Tire pressures?

Sarah
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Akasy




PostSubject: Air Filter   Thu Oct 21, 2010 7:46 am

makes a real difference on mine. Went to the Yam shop to get their filter oil and they don't carry it. Gave me some blue stuff that there techs use. Followed the directions put it back on and the puppy would not start--flooded a fuel injection engine! Took the filter off, started right up. Tried again and it did start but was way restricted. Cleaned the filter and went back to just plain oil and all is good. As my filter gets dirty my milage drops, change in tires results in slight drop--from stock to MT21's--air pressure does not seem to matter as long as it is above 15 or so. WFO seems to make the big difference.
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Jäger
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PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 12:18 pm

No, not tire pressure - I run them at the same pressure all the time.

Haven't changed filter oils, although it is true I haven't looked at the air filter during the time my mileage suddenly dropped. But the roads here have been unusually dust free this year due to the weather. I can't think of anything I've been through that would cause the mileage to drop that dramatically in such a short period of time. It's the first thing to check when I get back to the bike however, obviously.

Could a spark plug going bad cause such a sudden drop in mileage without being noticeable?
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motokid
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PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 12:43 pm

More ethanol in gas?

_________________
2008 WR250X
Gearing: 13t - 48t
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Eurastus

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PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 12:50 pm

motokid wrote:
More ethanol in gas?
My gas mileage drops every year about this time when the stations switch to the ethanol gas. I drop about 10% or so on all my bikes.

The OP is reporting a slightly higher percentage loss, though.

I'll bet it's a combination of the added ethanol and a dirty air filter.
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skierd




PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 3:04 pm

Winter gas and dirty air filter and/or oil. Or, not very likely, a leaky injector.
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f3joel

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PostSubject: Re: Hey! Where did my mileage go?   Thu Oct 21, 2010 7:18 pm

Maybe time for a new plug?
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Jäger
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PostSubject: Re: Hey! Where did my mileage go?   Mon Nov 22, 2010 3:24 pm

Well, got back home and cleaned the air cleaner as part of putting her to bed for the winter (-30... hello winter). Hardly any dirt at all came out of the filter, which is about what I expected given the mileage and road conditions since the last cleaning.

So... it isn't a dirty air cleaner.

When I get a bit more time to finish the process of tucking her away to bed, I'll include a spark plug change. Don't particularly feel like wrenching on the bike out in the present weather conditions.

It is going to be about six months before I actually ride the bike again, now that winter has set in. So the question of why my fuel mileage took a nose dive is going to be on hold for quite a while - and whether or not I solve the problem.

The question will probably nag me all winter.
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BluePill

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PostSubject: Re: Hey! Where did my mileage go?   Wed Dec 01, 2010 10:02 pm

Winter fuel is often reformulated for lower vaporization temperature and better starting. It lowers the btu value of the fuel. Your EFI system also senses lower air temperature and adds more fuel. That's why the bike produces more power in cold weather (Ummmmm................nice wheelies)

Combination will lower mpg. It should come back next spring. Don't fret.
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beemerwolf

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PostSubject: Re: Hey! Where did my mileage go?   Sun Jan 30, 2011 12:13 pm

in addition to those already mentioned (especially the diff in fuel composition)
remember that WIND has an extreme impact.

Look at it this way, even a lowly 10mph wind coming from the front can make your bike struggle a bit.

Also, when you are riding at roughly 60mph down the road, that same 10mph wind from the front can put enough force on your bike & you to reduce the mileage to what you might get at 68-70 mph speeds, in addition to making the bike feel a bit sluggish (remember, the bike seems like it is running at around 70mph---so a bit sluggish will definitely be the norm).

Hope this helps thumb
beemerwolf
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