FJR stock tank, trapped fuel & max distance

[Wee Willy]

Here's some more data:

These represent all my fill ups since I bought the bike new in Mar 2009. The dark line through the data is a LSQ regression of all the data points. Some points of interest (to me anyway):

• 83 data points, w/o sportos except the first fill at 150 miles & 5 gals (red circle @ 30 mpg). I suspect the ECU might run rich for the first few miles during break-in.
• The data is pretty well behaved after the first point and tends to an intercept very close to [0,0]...good news.
• There is some variance in mpg (x/y) but it's not bad: STD = 2.85 mpg
• Almost dead even split of points above and below the regression line--an indication of the low-skew nature of the underlying process...more good news

Where the dark regression line meets the spec 5.16 gal line (~203 mi) is where I would "expect" to see the "F" appear, but I tend to get it earlier than that at 190 or so. This could be from manufacturing variance in the level mechanism. I have not been capturing the point "F" appears and the distance run in reserve but I'll start.

So what does all THIS mean? Is it just mental masturbation?

Well, the STD is useful. Says I can expect a variation in mpg from tank to tank of +/- 5.7 mpg based on driving conditions if I use a 2 sigma threshold. That takes me from a low of 33.6 mpg to a high of 45.0 mpg and captures the great majority of my data. I saw 45 mpg only a couple of times and it was all slab @ "cruiser" speeds: 65-70.

But I want to know where my "cliff" is. And I want to try and discover the amount of the 6.61 gallons that is trapped (if any) in MY tank and can't be easily used. I need to capture some additional data: miles on "F" at refill and take the bike once or twice into the death zone. These are now on my list of things to do.

Back with more when I get some data.

W2

 

[phroenips]

Back with more when I get some data.
W2

Nerd. :nerd:

Doesn't mean I'm not fascinated.

 

[Big-B]

I managed to put 6.5 gallons in mine yesterday. :yahoo:

That was close......

 

[Wee Willy]

QUOTE (Big-B @ Apr 24 2010, 10:52 AM) <{POST_SNAPBACK}>
I managed to put 6.5 gallons in mine yesterday. :yahoo:

That was close......
How many miles total & how many miles on "F"? Do you recall?

W2

 

[Wee Willy]

I need to get a good picture of the fuel system at the tank. Can anyone point me to an exploded view or a cutaway? Or a functional block diagram? I'm curious about how it works and I don't have access to a service manual.

Cheers,

W2

 

[Wee Willy]

I've not been inside the tank and from some of the pictures here & there (i.e.: FJRTech) it's difficult to see how the feed system works. So I'm putting up a simple diagram for those who DO know how the system works so they can clue me in. Once I understand how the system functions I can accurately get what I need from the data as it becomes available.

First, consider this picture:

and this disclaimer: this is NOT meant to be an accurate depiction of the FJR's system. It is, instead, a model to be used to discuss what the real system does. For instance, I don't know if the system has 2 separate feeds, a main and a reserve; it doesn't need to have 2. It may only have a single feed with a float to decide when to show the "F" to the pilot. The actual physical representation of the FJR's system isn't important here.

For this discussion, consider the unaccelerated case (1g condition) of the bike sitting on its two wheels upright rolling down a level road at constant speed. This means we're going to ignore thrashing the bike around to keep fuel flowing for right now.

We will also ignore temperature effects on volume for this discussion...bulk temperature is a constant & doesn't change.

All the details below refer to the IML (inner mold line) of the tank.

Some definitions:

• There are 3 levels called out:
  Level 1 is the fuel level immediately after a full service with the fuel at the bottom of the ullage neck.
• Level 2 is the level of the fuel at the point the system declares itself to be on "reserve" and displays the "F" indicator to the pilot.
• Level 3 is the point where the fuel pickup in the tank can no longer reliably gather fuel in the 1g condition.

[*]There are 4 volumes called out:

• Volume "A" is the ullage volume in the tank. It is the air remaining in the tank after the tank is filled to the bottom of the ullage neck.
• Volume "B" is the fuel that will be burned before the system goes into reserve.
• Volume "C" is the fuel that is burned on reserve. The Yamaha spec declares this to be 1.45 US gal nominally.
• Volume "D", if it exists, is that fuel which cannot be scavenged by the fuel system at the 1g condition. This is the "trapped" fuel volume.

With this model in mind, I'll ask some questions in the next post.

W2

 

[Wee Willy]

Now, some questions for those who may know. Refer to P25 above for reference.

First, Yamaha declares the stock fuel capacity to be 6.61 US gal. I believe that refers to volumes B + C + D and DOES NOT include the ullage volume "A".

Next, does the FJR use a single feed with some sort of level mechanism for determination of the reserve condition? If so, what sort of level mechanism is it?

Next, in the level condition, is the feed at the lowest point in the tank and does the tank have clear pathways for all the puddled fuel in the low fuel condition to get to the feed? I used to own a Honda that had a tank shaped like a set of saddle bags. It had a feed on one side of the saddle and when you hit rock bottom, you could tilt the bike over to about 70 degrees and get a lot of fuel from the other side and do some more riding.

W2

 

[RadioHowie]

Now, some questions for those who may know. Refer to P25 above for reference.
First, Yamaha declares the stock fuel capacity to be 6.61 US gal. I believe that refers to volumes B + C + D and DOES NOT include the ullage volume "A".

No idea whether Yamaha counts that or not.

Next, does the FJR use a single feed with some sort of level mechanism for determination of the reserve condition? If so, what sort of level mechanism is it?

There is only one "feed". It's the fuel pump sitting in the bottom of the tank. There is no "reserve". That is simply an arbitrary display setting triggered by the position of the gauge float. Assuming manufacturing tolerances, i.e., slight differences in the "bend" of the float arm, one FJR might display 1 bar on the gauge while another may have started the "count-up-to-empty" with the exact same amounts of gas left in both tanks. That, unfortunately, is what makes this mental chess match particularly moot.

Next, in the level condition, is the feed at the lowest point in the tank and does the tank have clear pathways for all the puddled fuel in the low fuel condition to get to the feed? I used to own a Honda that had a tank shaped like a set of saddle bags. It had a feed on one side of the saddle and when you hit rock bottom, you could tilt the bike over to about 70 degrees and get a lot of fuel from the other side and do some more riding.

The FJR tank is relatively flat-bottomed so there is no "saddle bag" effect as you describe.

Here is a pic of the fuel pump's location in relation to the bottom of the tank:

.....and it's located near the apex of the wide "V" formed by the bottom of the tank clearly visible here:

....so there is very little area for gas to puddle and be "wasted".

And, since the tank IS so flat-bottomed where the fuel pump sits, I seriously doubt "leaning" the bike is gonna get an appreciable amount of gas to the pump, since the second you stand the bike upright, any gas sitting on that flat bottom is going to flow away and the pump starts sucking air.

The fuel pump IS at the lowest point of the tank, so when your bike starts spitting and sputtering, you're walking.

Thanks to Joe2lmaker for the pics.

 

[Wee Willy]

Nerd. :nerd:
Doesn't mean I'm not fascinated.

Thank you sir. I'm tetched. Really. B)

W2

 

[Wee Willy]

Thanks Howie. Good pictures.

I'm considering the bottom of the tank and the "sump bracket," the plastic item in the right of Joe's picture to see if 1/3 gal (more than a quart) trapped is reasonable. A quick "eyeball" measurement of the rectangular floor the pump is mounted on (10" x 12" est.) allows for a pint of fuel if the pump intake starts to suck air no more 1/4 inch above the level of the floor. You'll get a quart if the intake sucks air at 1/2 inch above the floor. So we're in the ball park.

Some assumptions here but they're not unreasonable.

Here is a pic of the fuel pump's location in relation to the bottom of the tank:

Any detailed pictures of the fuel pump available? I found this out there but it's a grainy exploded iso and tough to read.

Cheers,

W2

 

[painman]

This is all quite fascinating and good info but personally I fill the bike on the side stand to keep enough headspace in the tank to allow proper venting of the tank and try not run the tank low enough to cause the fuel pump to over heat and to keep from calling a tow truck if one is near because I ran out of fuel like a knucklehead.....PM. <><

 

[RenoJohn]

And, since the tank IS so flat-bottomed where the fuel pump sits, I seriously doubt "leaning" the bike is gonna get an appreciable amount of gas to the pump, since the second you stand the bike upright, any gas sitting on that flat bottom is going to flow away and the pump starts sucking air.

I've had the thrill of running my superior Gen1 dry a few times ...and I can say that my wild thrashing-about as the pump started to suck air didn't get me far compared to other bikes. so, Radioactive Howie is very correct on this. When I say "thrashing about" I'm referring to leaning the bike back-and-forth to "splash" puddled fuel to the fuel pump inlet.

On some other bikes this is extremely effective (to the tune of about 20miles on my V-strom) , but because of the good design of the FJRuel tank, not so effective here.

[That will also vary depending on the bend of the float in the tank that seems to vary on bikes pump, and other unforeseen complications...I find it far easier and to just get gas when it starts flashing.

Yes, and because that "bend" is very likely to vary considerably from bike to bike, any comparison data is likely to cause more harm than good. Get to know your own bike, not your neighbor's. Kinda like a wife.

But unlike a wife, your particular "bend" can be corrected/modified with just a little tweaking if you feel the need.

[*]Volume "A" is the ullage volume in the tank. It is the air remaining in the tank after the tank is filled to the bottom of the ullage neck.

....I believe that refers to volumes B + C + D and DOES NOT include the ullage volume "A".

I've always wondered about this, and in my own mental masturbation during many many fill-ups ---Uhh, I have convinced myself both ways and continually go back and forth in my belief. Amazing the things one thinks about on lonely miles. I hope this question never gets answered, as I'll have nothing to think about when riding.

finally, am I the only one that thinks that Willy's graphs and drawings and stuff are totally groovy? We don't see a lot of fancy stuff like that up here in Northern Nevada.

 

[Fred W]

To further complicate matters, completely independent of variables of fuel mileage, I have experienced that the "reserve sensor" circuit is prone to activate at varying fuel levels on a given bike (mine) depending on certain external conditions.

Normally, if I fill my bike right after it goes into "reserve indication" I usually put in 5.1 -5.3 gallons. Just yesterday I stopped soon after it counted down to 1 bar, but before it started flashing because I was going into a stretch of road with unknown fuel availability, and filled it with over 5.5 gallons. This has happened a few other times as well. I always fill it the same way (completely, can't fit any more), and we don't have vapor recovery hoses at the pump around here, so there is not that much possible variation in the full level.

I'm sure that you've noticed that the fuel gauge will display much lower on the side stand. But when you tip the bike up to vertical it takes quite a while for it to register the (correct) higher level. There is some sort of a very long time constant hysteresis built into the metering circuitry to prevent the gauge from fluctuating wildly. I think that this circuit will effect the gauge display, and thereby delay the onset of the reserve mode indication, when riding curves and sloshing the fuel around compared to when riding more sedately or droning down the highway.

So, what does this mean? I think you need to consider several things when trying to stretch a tank out to the next gas station. Just looking at the mileage countdown on the odometer compared to your average mpg may not be adequate if the reserve happens to come on later than normal. I'd also weigh the total mileage on the tank, and what kind of riding you have been doing when trying to decide how far to figuratively "push it" if you don't want to literally.

 

[Wee Willy]

....I believe that refers to volumes B + C + D and DOES NOT include the ullage volume "A".

I've always wondered about this, and in my own mental masturbation during many many fill-ups ---Uhh, I have convinced myself both ways and continually go back and forth in my belief. Amazing the things one thinks about on lonely miles. I hope this question never gets answered, as I'll have nothing to think about when riding..

Tell you why I think there's a very good chance it's B + C + D:

First, ullage: this additional space is included to compensate for the change in volume that occurs in liquids with changes in temperature. The rate of specific weight change with temperature of unleaded gasoline is pretty much a constant across the typical temps the fuel encounters on the bike: call it -4.05E-3 lbm/gal/deg F.

I have a black tank that sometimes sits in the Palmdale, CA sunshine. It can approach 115 deg ambient out here in the summer. And the bulk temperature of the fuel after soak will be significantly higher than ambient. I've had it sit all day after a fill to the bottom of the ullage neck and no fuel escapes via overflow. I know this because I've checked as I pass the bike...it's the engineer inside that won't let me go.

If the fuel temperature at fill is 60 F (not unreasonable for underground tanks, even in the desert) and the final soak temperature is 140 F (hot Palmdale sunshine) then the change in fuel volume will be on the order of 6.2%. I don't know what Yamaha's design specs were, but I would guess you would want even some margin on this number. Consumers don't like to see gasoline dribbling out of the bottom of their expensive machine in any situation...right? So let's guess & call it 7.5%. If I advertise 6.61 gallons capacity and then only give you 92.5% of that (6.1 gal) owners would notice the missing 1/2 gal. And as a program manager responsible for, among other things, keeping marketing in bounds, I would insist we publish only the "fillable" amount in our documents.

Next, consider the related mileage argument. That 1/2 gal is worth about 20 miles on average. As a consumer, I want that 20 miles on my side of the equation, not promised then not delivered in some instances. So based on these and other considerations I'm too lazy to put up, I believe it is a safe guess to assume the 6.61 gal is B + C + D as indicated above.

I can see light at the end of this tunnel now. There IS a way to statistically determine with good accuracy (few percent?) what each individual bike is capable of regarding range on the stocker tank WITHOUT having to pour your gasoline all over your garage floor. It will necessarily require driving the bike a significant distance into the reserve zone a statistically significant number of times. You might even want to hit rock bottom a time or two to "confirm" the analysis as to the cliff's location but that's not absolutely necessary. The data that needs to be collected is the following:

Distance driven on reserve

Total distance on this fill

Amount of fuel to refill

With enough solid data points (at least 10) like these on hand you can characterize YOUR system pretty effectively. More data points will deliver more "accuracy." I can even see creating a table that contains estimates of remaining distance based upon where you went over to "F" and characterized by YOUR bike's specific tank situation.

I'm going to start collecting this type of data as I ride and I'll put the results up here as they become available.

Cheers,

W2

BTW Reno, thanks... :hi:

finally, am I the only one that thinks that Willy's graphs and drawings and stuff are totally groovy...

 

[charismaticmegafauna]

First, ullage: this additional space is included to compensate for the change in volume that occurs in liquids with changes in temperature.

I learned a new word...

Next, consider the related mileage argument. That 1/2 gal is worth about 20 miles on average. As a consumer, I want that 20 miles on my side of the equation, not promised then not delivered in some instances. So based on these and other considerations I'm too lazy to put up, I believe it is a safe guess to assume the 6.61 gal is B + C + D as indicated above.I can see light at the end of this tunnel now. There IS a way to statistically determine with good accuracy (few percent?) what each individual bike is capable of regarding range on the stocker tank WITHOUT having to pour your gasoline all over your garage floor. It will necessarily require driving the bike a significant distance into the reserve zone a statistically significant number of times.

On a related note: (reportedly...) Honda, decades ago, did something similar when it calculated the average distance, in the U.S., between gas stations -- so they could determine the distance (for each model) a bike needs to be able to go on 'reserve'; and, thus, the height of the stand-pipe on the pet-****.

On another related note: my friend's new BMW R1200GS shows, on the dash read-out, the miles you can go 'till you run-out-of-gas (not, like the FJR, how far you've gone on 'reserve'). He ran further -- into 'negative miles'...

 

[Crash Cash]

We could do this the mythbusters' way (hopefully minus any explosions) and connect a hose to the fuel pump output, fill the tank, then put +12v to the pump until the tank emptied, then measure the output, and check for any dregs left in the tank. You'd need to be careful to have a suitable output for the high-pressure gasoline stream, and not smoke in the meantime, but I don't see too many problems. The bike would be on the centerstand with the front wheel propped up so it's reasonably level.

I have a 12v model airplane fill-up pump that could be used to pump out the dregs for measurement. And of course, posting this probably means I'm getting volunteered...

 

[Fred W]

You could just go into the DIAG menu and turn on the fuel pump.

 

[Wanderer]

While I'd love to have the graphs to track it, all I can offer is my historical data.

I normally ride above 5k ft ASL, am not prone to wildly jacking the throttle open and try to carry as little crap as neccessary.I also cram as much fuel in my tank as I can especially when I'm on a long ride and going to burn it before it gets hot and expands.

Last week I rode home from Prescott, AZ, filling up there I took the lazy interstate. Cruising 75-78 passing at 80-85 I hit the F-trip at 254.x miles, pulling into the gas station in Gallup NM at exactly 272.0 miles. Checking the reciept, I put in 5.44 gal for an MPG of dead-on 50. Subtracting the 18 miles on 'reserve' x 50mpg that means I burned 0.36g. leaving almost exactly 5g on the reg guage.

I'd estimate thats historically in line for *my bike*

if we estimate the usable fuel = 6.1g , that means I had .66g left to ride out, or another 33 miles then I become a pedestrian. 33+18=51, so the reserve flashers warn you at 1g remaining. That's been my expeience.

Because I've gotten as poor as 36mpg and as good as 58-60, I guesstimate my Dis To Empty by dividing the total miles traveled by 5 gal and and on the fly figure my fuel economy and how far i have left on that particular tank. So far It's been pretty much spot on.

 

[NSrider]

I have gone as far as 46 miles while on reserve and that was 2-up fully loaded. Looking at some of these post's it's obvious my MPG is much lower than what some of you are getting.

Just to show the differences between bikes, last year at CFR I was riding with Joe2lmaker and moosehead. We all filled our tanks in the morning when we headed north to visit an hydro dam. When we realized that we were not going to make it too the dam with our remaining fuel we turned around and headed back. When we got to the gas station both moosehead and myself were around 30-40kms into our reserve while Joe2lmaker was just getting into his but still all three bikes took the same amount of fuel.

 

[Harald]

On another related note: my friend's new BMW R1200GS shows, on the dash read-out, the miles you can go 'till you run-out-of-gas (not, like the FJR, how far you've gone on 'reserve'). He ran further -- into 'negative miles'...

My truck can go 50 miles after empty! :yahoo:

That's a good thing because it only gets 10mpg while running, so those free miles after empty really help with the fuel costs. <_<

It really sucks filling a 38 gallon tank when it's empty! :dribble: