Gas Mileage dropping - no reason I can see

I had a major tune-up last October, and, since then, the bike (FJR 05, 77kmiles) runs really well. Smooth, even acceleration.

I keep meticulous records about my fuel use. In summer, it gets better - as much as 48mpg when it is really hot. In winter, it gets worse, sometimes drops to 39 or 38. I always thought that was weird...but that is not the problem.

My mileage is starting to suck. My last tank was 35.1 mpg, and that is the lowest tank average since I have owned the bike. Last 8 tanks have all been under 40mpg. I am doing NOTHING different - normal commutes.

I checked air in tires - normal. The October tune-up definitely included an air filter cleaning. I have replaced the gear oil in the final drive twice - last time was at 62k.

I said to myself, "Self, could it be wheel bearings?". I did a search today, and I find that the concensus for the Forum is that the stock wheel bearings are quite sturdy and could last a lifetime. Given that - I have NOT checked them by feel yet. I will at earliest opportunity.

What else could cause a drop in fuel efficiency in the bike? Anything else I can look for while I'm taking off the wheels?

Some seasonal variation is normal. I have experienced that on all my high-gas-mileage vehicles: Prius, 2 ST1300's, NT700, and the FJR. Though not to the degree you're describing.

But the unexplained drop could be caused by problems in the electrical system, believe it or not, including battery misbehaviors. Do you have a way of measuring system voltage while you're riding?

Check for brakes dragging on either front or rear

I assume you're actually doing the math to check your mileage not relying on the bikes onboard trip computer right?

Here in PA we get a different fuel blend in the winter and it plays hell on my fuel mileage, both bike and car. Ethanol content makes a difference as well. Have you tried changing brands of fuel? If so does it make any difference? Are there any other problems with the bikes performance or driveability?

Have you noticed any similar changes in any of your other vehicles fuel mileage? I know all of this may sound vague but I just want to make sure you eliminate the fuel itself as the source of your trouble before delving too deeply into the bike.

2005? What onboard computer?

Yeah mine is pretty bad as well. I am getting anywhere from 35-37 mpg. I have 103,xxx miles on mine. I am pretty sure that mine will be better after my valve adjustment. My bike runs great, but it just sucks the gas.

Fred W said:

2005? What onboard computer?

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Sorry.

So used to my Gen 2 dash I didn't think that one through.

Good call about a dragging brake.

did your favorite station just start adding ethanol?

Change windshields recently?

I always put the barn door on in the winter and I know this is part of the reduced mileage I get in the winter.

Don't think I ever got above 45 mpg. 40 was pretty much my average.

Same here. 40-42 in regular summertime riding. 34-36 when in full mountain hoon mode.

36-38 riding easy in the winter months (hard to get too crazy with the crappy road surfaces) with cold, heavy air, big wind shield and winter gas formula.

Unless you're experiencing other drive-ability issues... it's winter blended fuel.

You're taking the wheels off to check bearings? They are sealed ya know! Just put the bike on center stand, check for binding or slop. If they're so far gone as to be dragging down engine and fuel economy it will be obvious.

My 06 with an 08 engine runs strong and great.

Today I saw a low mpg tank of 28, yes 28 and a high of 40.1.

BTW, a 'tank' is 11 gallons, so it's a nice long time to average the mpgs.

The OP noted a change in behavior, so that's the real focus. Here's something that happened to me on both ST1300's I had: The thermostats stuck (at least partly) open. This caused the gas mileage to suffer, pretty much as described by the OP. No other apparent symptoms but this. It didn't become apparent until the cooler fall weather arrived. And you had to know the bike to notice the effect. In both cases, simply replacing the thermostat got the bike back to normal.

RichDoyle said:

The OP noted a change in behavior, so that's the real focus. Here's something that happened to me on both ST1300's I had: The thermostats stuck (at least partly) open. This caused the gas mileage to suffer, pretty much as described by the OP. No other apparent symptoms but this. It didn't become apparent until the cooler fall weather arrived. And you had to know the bike to notice the effect. In both cases, simply replacing the thermostat got the bike back to normal.

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Funny you mention this, my wife's Mazda did the same thing.

I have a 4000 mile 2010 and I don't believe I have ever seen more than 34 mpg. I normally ride 10-15 mph over the limit. Just wondering if there has been a average for our bikes

I finally got some time to do some checking on the wheels. Before I get to that, I must rant.

I have another thread about the major service I had done to the bike last October. I know that the shop took off the front wheel. This is the first time I had a chance to lay a wrench on the bike since then. And I very nearly destroyed the stupid bolts that hold the brake calipers on trying to get them off. I have had the front wheel and brake calipers off MANY times, and I always put them back on and make them about as tight as I can - by hand, with an open-end 12mm wrench. And I will maintain that THAT IS TIGHT ENOUGH! I don't know what tool that shop used to tighten those bolts, but it was too much!

Rant off.

I took the calipers off and spun the wheel. If I hadn't stopped it, it probably would still be turning. Bearings are FINE. I put the calipers back on - and, of course, spread the pads to get them back on. Spun the wheel, spins easily. Squeezed the brake lever a few times and spun the wheel - I get about 2.5 to 4 turns before it stops.

While off, I looked at the pistons on the calipers, and they are Grody! Grody to the Max! I did other searches in the forum and found a couple of threads that indicate that a rebuild, new seals, piston cleaning, etc. is not a bad idea every couple or three years. I've done that job - once in 10 years. (blush)

I am thinking that I might want to do that job again - the full caliper service.

Here are my questions for the forum: Are there any good links that show me exactly what I want to do? Pictures, movies, detailed descriptions?

One question I have - should I try to do the whole job with the calipers still attached, or should I completely remove the banjo bolt that holds it on. Obviously, I'm going to need a full brake fluid change either way.

Where do I get the parts? Ron Ayers is mentioned in a few threads. I went to the site and looked for a full brake rebuild kit. Maybe I just looked for the wrong thing, but found brake pads or rotors, no kits. The link to YamahaSportsCenter in Longview didn't help either. Didn't see anything on Amazon.

I have a Mityvac that I've used to bleed the brakes before, and it worked. I always wondered, though - why fill the reservoir and suck the fluid down, instead of starting at the bottom and push the fluid up? Maybe that is a whole new thread...

I can't wait to read the responses!

birkdale10 said:

Spun the wheel, spins easily. Squeezed the brake lever a few times and spun the wheel - I get about 2.5 to 4 turns before it stops.

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This tells me that this probably isn't the reason for your lowered MPG.

birkdale10 said:

One question I have - should I try to do the whole job with the calipers still attached, or should I completely remove the banjo bolt that holds it on. Obviously, I'm going to need a full brake fluid change either way.

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Take them off the brake lines, else you'll risk damaging the brake hoses. It is much better to rebuild the calipers on a work bench than crouched next to a dangling pair.

birkdale10 said:

Where do I get the parts? Ron Ayers is mentioned in a few threads. I went to the site and looked for a full brake rebuild kit. Maybe I just looked for the wrong thing, but found brake pads or rotors, no kits. The link to YamahaSportsCenter in Longview didn't help either. Didn't see anything on Amazon.

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I don't know if you'll find a "kit" per se ... all you need are pads, banjo washers and piston seals.

birkdale10 said:

I have a Mityvac that I've used to bleed the brakes before, and it worked. I always wondered, though - why fill the reservoir and suck the fluid down, instead of starting at the bottom and push the fluid up? Maybe that is a whole new thread...

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If you have a large syringe, you can use this to push fluid up.

Try just cleaning the pistons (well) before you go through all the trouble of replacing the seals. It's pretty easy to do on a 1st gen with the larger pistons. Just use fluid pressure to push the pistons out past the "grody" point and then use a toothbrush and spray brake cleaner to get them sparkly clean.

To get to the back sides of the grody pistons I use a set of external (expanding ones on the left below) snap-ring pliers without the little tips in them and put the heads of the pliers inside the hollow pistons. These give you a good grip on the pistons to rotate them in their bores.



What you are looking for (after cleaning or before for that matter) is, with the caliper in your hand, watch the pistons action when you lightly press and then release the brake lever. You should see the pistons barely retract back into their bores a hair when the lever is released. That tells you the seals are still good, doing their jobs and the pistons are not hanging up on road spooge.