Seriously bad gas mileage.

[puppychow]

Over the past few tank fulls or so, I have seen gas mileage of 30-33 mpg. I used to consistently hit 40mpg prior to this. I just ran a tank full of Yamaha Ring Free this last time, in case the fuel system needed cleaning, but the mpg has remained really bad.

No significant change in riding style or throttle application.

No change in type of gas or how I fuel up.

Tire pressures meticulously checked before every ride and remain consistent.

Brakes are not dragging, I checked. Wheels turn freely when brake not applied.

Throttle position sensor which was replaced recently still reads 16-100 in diag mode.

What are the usual suspects?

1. Fuel pressure regulator?

I have a mity vac, but I have never used a pressure gauge to check the fuel pressure. Any tips here? Can I go to the neighborhood auto parts store and buy just any pressure gauge? What about the adapter to attach the pressure gauge to the fuel line, that the service manual mentions? Where do I get that?

2. ECU running the mixture rich?

Does it think the bike is still cold and enriching the fuel mixture? The RPM's drop down to normal ~1100-1200 rpm when the engine warms up. Does that mean the ECU doesn't think it is still cold or do I need to do more testing?

What else?

I am going to pull the spark plugs today and see how they look. I replaced them last year so they have about 14K on them, but this mileage problem has been pretty recent, like the last 4 tank fulls, so I am not sure if running rich for 4 tank fulls will show any significant symptoms on the spark plugs. Pulling them anyway to see.

 

[rogdeb]

If you always used the same gas station, maybe the pumps are faulty ? Hell of a wild guess I admit.

 

[dcarver]

The plugs will be perfect. The bike is fine. The holidays put another 50 pounds on that lard ass of yours and that's why the mileage dropped.

I bet you've been riding in the flat lands (low elevation) and not the hills so much (higher elevation). That, with Ca winter gas, will take your mpg into the low 30's. I routinely get 34 - 36 mpg.

FWIW!

 

[NMRoadRunner]

Cali gas formula change recently? More ethanol? just guessing. Here the fuel smells like a bad batch of moonshine there so much corn squeezins in it.

 

[puppychow]

I have only filled up at Chevron stations. This is Cali gas, so I am guessing they all pretty much have the same real gas to ethanol mix.

Yes, pretty much been riding the flat-lands of Kalifornistan, or under 2000' feet anyway.

I haven't pulled the plugs yet, but if they are fine, and I suspect they would be fine, I will run a couple more tanks this weekend and see what the mileage does. If, however, it is easy to check the fuel pressure regulator while I have the tank up, might as well do it. So any tips or advise on that would be helpful!

Thanks!

 

[El Toro Joe]

Winter gas...yer mileage should go up in the spring.

 

[Fred W]

Rear brake draggin? I usually lose a few mpg on the winter gas formula. It isn't just the ethanol percentage.

 

[MCRIDER007]

I've heard that O2 sensors don't last forever....assuming you are not using a power commander....which I would suspect would be the cause if you were.

 

[puppychow]

Maybe just winter gas and I am just paranoid.

Will report back later. Thanks!

 

[FJRBluesman]

Did you swap windshields or add a trunk? I run the giant barn door V-Stream in the winter and my Givi trunk, my MPG falls off 2-3 gals off my normal 40MPG.

Also, subtle changes in speed/acceleration can vastly affect your MPG. A few quick snaps of the wrist to pass folks etc adds up quickly. At frwy speeds to work I get 40mpg, it gets better on back roads due to speed. Drops in winter due to flying my barn door windscreen.

 

[RossKean]

I had an oxygen sensor issue (pinched wire) that resulted in very poor fuel mileage. Other symptoms included poor running at low RPM and a highly fragrant exhaust. I think you would have other indications as well if the O2 sensor was FUBAR. By all means, check the plugs and keep an eye on mileage for the next little while but winter fuel formulation can make a significant difference.

As far as I know, there is no easy way to check the O2 sensor for correct operation??

 

[SoCalFJR1300]

I'm in So Cal and haven't noticed any mileage drop since we started the "Winter" fuel.

I consistently average about 45MPG if cruising the slab at 80MPH.

If I'm riding hard with a group I still average about 41/42MPG.

Other than trying different gas I have no other ideas for you, sorry.

 

[RichDoyle]

Something I ran into with two ST1300's was stuck-open thermostats. That caused a significant drop in gas mileage in both.

 

[r1byker]

I hope you don't have what happened to me; carbon build-up on the valve seats that was holding a couple exhaust valves open. It required a top-end job to repair. I had noticed that my fuel mileage had dropped about 5 mpg but everything else checked out okay. The bike ran great but it was when I took the bike in for a valve adjustment that the shop discovered the problem. I only run Chevron gas and almost all my riding is on the highway so it's a mystery what caused the carbon build-up.

 

[dcarver]

PC, if if you decide to check compression/leak rate I have all equip you need and will let you borrow.

I doubt carbon under valve is your problem though.

 

[Justin]

I was getting about 10 Mpg once the old hack riding down 395 once towards Reno :lol: . Those Cali winds don't help.

 

[Bluestreek]

How is the air filter?

Most likely winter gas. Me think.

 

[radiummadman]

you do not need to run a full tank to check this problem. I always watch the fuel gague as it drops from one setting to the next. Usually get

at least 30 miles before the first bar drops on a Gen 1, and average 30 miles per bar. I got some bad gas once, the bike ran fine BUT first bar

dropped at 22 mpg, so got Seafoam at next stop, returned home drained the tank, reloaded with good fuel & more Seafoam & all was fine.

Not anal but I can tell by the bar drop compared to mileage from last fill up weather I am being a hoon or not or have problems.

 

[Silent]

I'm in So Cal and haven't noticed any mileage drop since we started the "Winter" fuel.
I consistently average about 45MPG if cruising the slab at 80MPH.

If I'm riding hard with a group I still average about 41/42MPG.

Other than trying different gas I have no other ideas for you, sorry.

Damn, I"m luck to get 30