Sudden decrease in gas mileage

[topangster]

My S2R 1K has averaged 42-44 MPG since I bought it a year ago.  This despite installing a Spark midpipe and cored cans last year.

But my last three fill-ups showed I'm now averaging 36 MPG - big drop.  At first I thought it might have been due to riding in cold weather and hence having a richer mix, but it's been quite warm here in So Cal for the last two weeks so that's not the issue.  No other changes to the bike in the meantime.

Any ideas on what could be the culprit here? 

[Raux]

are you filling at the same station? not sure, but wouldn't bad gas bring a drop in fuel economy.

[zooom]

are you turning your right hand more?

[Porsche Monkey]

Have you been riding in traffic more than usual?

[DucMouse the Mighty]

are you turning your right hand more?

+1

i have the same problem with gas milage and its probably due to my lead right hand....and also getting use to using all that power i dont need

[topangster]

I have been riding in a bit more spirited fashion lately .  But I don't think that's it, too dramatic a drop.  Not a lot of traffic, either. 

It got really cold here a few weeks ago, though, and I rode quite a bit in that weather (low to mid 40s - okay, cold for us pansies in L.A...)  My bike didn't start right up like it usually does one morning, then that happened again the next day (when it wasn't as cold.)  I'm wondering if maybe the ECU did some kind of reset at that point to richen the mix, and now hasn't re-adjusted.  That possible?   I could disconnect the battery to let it reset, but don't really want to if it's an unlikely explanation...

[Gus Duc]

Maybe your RB O2 emulator took a dump........ When I was running my OEM ECU & I unplugged the O2 sensor, bike would run great & get continually richer until it ran worse than when it was lean.

I'd put my money on the Emulator & I'd try resetting the ECU to see if that clears any adaptation that might have occured.

Good luck

[rockaduc]

I have been riding in a bit more spirited fashion lately .  But I don't think that's it, too dramatic a drop.  Not a lot of traffic, either. 

It got really cold here a few weeks ago, though, and I rode quite a bit in that weather (low to mid 40s - okay, cold for us pansies in L.A...)  My bike didn't start right up like it usually does one morning, then that happened again the next day (when it wasn't as cold.)  I'm wondering if maybe the ECU did some kind of reset at that point to richen the mix, and now hasn't re-adjusted.  That possible?   I could disconnect the battery to let it reset, but don't really want to if it's an unlikely explanation...

Gets my vote for your reason.  You'd be surprised...

[Popeye the Sailor]

My S2R 1K has averaged 42-44 MPG since I bought it a year ago. 

But my last three fill-ups showed I'm now averaging 36 MPG - big drop. 

42-36 isn't that big a drop. Keep flogging it 

[Drunken Monkey]

42-36 isn't that big a drop. Keep flogging it 

Yeah. I see up to 60 on the highway (a well tuned '01 900 with a PC III) and as low as 30 if I'm doing nothing but spirited short trips in the city. Your change seems well within the bounds of normal.

It could also be your gas station switched to using more Ethanol for the Winter months. I've seen as big as a 10% loss in gas mileage due to the added corn juice.

[topangster]

It could also be your gas station switched to using more Ethanol for the Winter months. I've seen as big as a 10% loss in gas mileage due to the added corn juice.

No kidding?  Didn't think of that.  Although I filled up at different stations lately, so that doesn't sound too likely. 

Didn't realize pushing it just a bit more could affect mileage that much.  I got clip-ons recently, which definitely changed my riding position and enabled me to ride faster on my usual roads - pretty big difference, actually.  [moto]  But a good chunk of my recent riding was freeway, too, and at no faster than usual speeds. 

I'm thinking GusDuc may be right - my RB O2 Emulator might have made some adjustment or has somehow affected the ECU.  The change in mileage is date-coincident with the weather changing (it started running much richer then), and it hasn't switched back.  It's running great otherwise - lots of power where I need it, nice and smooth at lower RPMs, no lurching at all.  All feels like a siginficantly richened mix.  I'm going to try disconnecting the battery and see what happens...

[Massinova]

Yup, I was going to say the same thing ...station moved to "ethanol" blend

[Gus Duc]

No kidding?  Didn't think of that.  Although I filled up at different stations lately, so that doesn't sound too likely. 

Didn't realize pushing it just a bit more could affect mileage that much.  I got clip-ons recently, which definitely changed my riding position and enabled me to ride faster on my usual roads - pretty big difference, actually.  [moto]  But a good chunk of my recent riding was freeway, too, and at no faster than usual speeds. 

I'm thinking GusDuc may be right - my RB O2 Emulator might have made some adjustment or has somehow affected the ECU.  The change in mileage is date-coincident with the weather changing (it started running much richer then), and it hasn't switched back.  It's running great otherwise - lots of power where I need it, nice and smooth at lower RPMs, no lurching at all.  All feels like a siginficantly richened mix.  I'm going to try disconnecting the battery and see what happens...

Thanks man.... could you says the words to my wife...... according to her I'm never right

[NAKID]

42-36 isn't that big a drop. Keep flogging it 

Dude, that's a 15% drop...

[Jobu]

Valves could be getting out of spec.  That would lower the gas mileage some.  Of course I have no idea how many miles it has been since the last service.

It is probably a combination of several things mention thus far.  And as DP said, if stations are using more ethanol in your area, you could see a significant drop form that.