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-   -   sudden big drop in MPG (http://www.advrider.com/forums/showthread.php?t=842116)

trc.rhubarb 11-18-2012 08:38 AM

sudden big drop in MPG
 
Bike has ~52.5k miles on it and runs great. It's a bit noisy and has been since I picked it up a year ago. One day I'll get around to ordering new cam chain tensioners.

Anyhow, I've generally gotten in the high 30's and sometimes even mid 40's for mileage but the last 3 tanks of gas (over the last 5 days) have been in the low low 30's. Even the bike knows something is up and shows 31.x mpg on the screen after a reset of the average.

It runs well and accelerates fine, no carbon build up on the bags or muffler.

air filter changed, plugs checked, valves & tb were done and checked good at 48k. FD fluid was changed then and there is no freeplay. No noises in the driveline when rolling in neutral. Checked for drag on front and rear wheels. Brakes aren't hot after riding. New rear tire was put on just before the issues started but the tire looks good and is still at 40psi; front good too. The only other change is that it's been raining.

What's next to check?

LaurelPerryOnLand 11-18-2012 09:01 AM

Observations about COLD for an RT...
 
http://bmwsporttouring.com/ubbthread...555#Post808555

Rinty 11-18-2012 09:22 AM

Quote:

What's next to check?
Oxygen sensors.

But I would just have the whole system scanned.

trc.rhubarb 11-18-2012 08:46 PM

Thanks, I think too much for it to just be the cold. In fact, since it's been raining, it's not been that cold.
O2 sensors will be interesting to test. I guess I'll see if it gets better first.

kk3an 11-18-2012 09:06 PM

I had the same symptoms at about 38,000 miles, and replacing both oxygen sensors made the mileage pop back up.

Looking back, I'm not sure if just a simple cleaning of the sensor area itself will cure this or not, or if a total replacement is needed.

Dan

tjt94 11-18-2012 09:29 PM

It is because of winter blend fuel. I always lose about the same is California is the winter.

El Gato 11-18-2012 09:37 PM

Quote:

Originally Posted by tjt94 (Post 20074368)
It is because of winter blend fuel. I always lose about the same is California is the winter.

That was my initial thought as well, but CA switched to winter gas early this year -- about 6 weeks ago on an exemption from the governor due to the Richmond refinery fire.

tjt94 11-19-2012 07:48 AM

Quote:

Originally Posted by El Gato (Post 20074398)
That was my initial thought as well, but CA switched to winter gas early this year -- about 6 weeks ago on an exemption from the governor due to the Richmond refinery fire.

That may have been how long it took to deplete the tanks. Regardless, the difference in actual cost between they mileage figures is not that much so keep an eye on it. If it is running fine just ride. Good luck.

twwhitey 11-19-2012 09:11 AM

Interesting - I just reset the MPG calculator yesterday and noticed I was pulling at best 37-39 MPG doing some simple highway cruising. Definitely recall getting much better than that here in SoCal a few months ago. F'n winter gas indeed..

trc.rhubarb 11-19-2012 11:30 PM

Bike is running well just bad mileage. I don't ride my other so much but I think I'll switch for a week and see if it's getting bad mileage too. That would show for sure it's the gas. Thanks for the input!

Tmaximusv 11-20-2012 08:27 AM

cap?
 
I scanned this thread earlier and didn't have anything to offer...I just remembered something to offer.:D

If your gas cap isn't sealing properly, you can lose about 40% of your fuel to evaporation (under warm conditions) DAMHIK.

trc.rhubarb 11-20-2012 01:01 PM

Quote:

Originally Posted by Tmaximusv (Post 20083738)
I scanned this thread earlier and didn't have anything to offer...I just remembered something to offer.:D

If your gas cap isn't sealing properly, you can lose about 40% of your fuel to evaporation (under warm conditions) DAMHIK.

O'ya, went through that one befure :) Funny how you can keep smelling gas and 'wonder where it's coming from'

ukdave 11-24-2012 05:59 PM

I had a leaks from fuel pipe connections more than once.

trc.rhubarb 11-24-2012 08:37 PM

Good one to check. Even though I'm not smelling gas, it could be leaking. Hopefully my new shocks arrive this week and I can just take the whole thing apart.

Multiplicity 11-30-2012 11:02 AM

You should also treat the fuel with Techron every 10K miles to keep the injectors clean.

Buy a bottle at the local parts store :pynd


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