Need help in figuring out a fuel problem.

[dakota49]

I have a 2004 FJR1300 that I purchased new in October of 2003. I have 139K miles on it. With the exception of mechanics doing test drives after service, I have put all the miles on it. I say this to emphasize that I know when I have filled my gas tank completely full. My daily ride ends with me topping off the tank to ensure the tank will be full in case the weather turns bad and ends my riding season. I fill the tank and ride the 2 miles home. The last four tanks before season’s end went like this. I filled the tank and rode the 2 miles home and when I started the bike for the next ride, I was already down a single bar on the gas gauge. That amount should have yielded at least 34 miles instead of the 2 that were on it. I noted it but dismissed it as some sort of fluke. The next 2 tanks went normally. The most recent tank at season’s end was again down the 1st bar on the gauge with only the 2 miles on the tank when I fired it up. I decided to ride until I used up the second bar and to then top off the tank. The second bar got me to a total of 34 miles on the tank. When I topped it off, it took 1.6 gallons which should have gotten me a bare minimum 54 miles on the tank. I think all four tanks were filled at the same gas station, an Exxon which is where I normally fill. There is never ANY gas smell and I’ve had my shop check for leaks. There are none. I’ve had my oil professionally analyzed for fuel content and there is none. Someone said the problem may be that the temperature of the gas at fill time might be very warm and after overnight parking in a garage that got down to 45 degrees overnight, the gas might be contracting. First of all, I can’t believe it would contract that much and secondly, this has been my routine for over 20 years and it has not happened before.

Any ideas?

 

[RiderJoe]

How much time passed between the “last” fill-up to the “next ride” when you noticed the the fuel level being lower? Also, do you fill the tank with the bike on the center, or side stand?
My thinking is that if you top off the tank with the bike on the side stand, then (in my experience) the tank isn’t filled as much as when it is filled on the center stand. Your bike is also older, with many miles, so it is possible that the tank filler’s gasket isn’t sealing as well as when it was newer after so many fill-ups and the rubber seal’s aging. So, it is possible that the combination of lower fuel level to start with and (possibly) several months of sitting with slow evaporation may be what contributes to your experience?
In any case, I wouldn’t be very concerned - there are no leaks, and no fuel in the oil either, so the issue is probably due to fuel evaporation.

 

[SkooterG]

Well, my guess is the O-ring in the return line in the fuel pump. It's a known issue for the older Gen I FJRs. It gets old and brittle/deformed/cracked and fuel starts leaking. What is odd is no smell of fuel. Perhaps just because it is leaking so slow. It's a stupid design by Yamaha imho.

There is no way that temperature is making that big a difference. Nor do I think it is evaporation. That would be a LOT of evaporation. I think you have the fuel pump leak. It is just so slow that it is not noticed unless over a long period of time.

This thread on FJROwners might be helpful: https://www.fjrowners.com/threads/fuel-leak.153544/#replies

 

[RossKean]

I have a Gen II, but I have always found the first bar to be quite variable. Your issue might have more to do with the gauge than anything else. I also find worse mileage in winter months due, in part, to winter blend gasoline. Last, but not least, I find short rides (especially in cool weather) yield abysmal mileage, especially if the bike is not fully warmed up.

I realize you are not new to FJRs or your bike in particular but I am not terribly surprised by what you reported. (I have a total of 300,000 miles on the two Gen II FJRs I have owned.)

 

[dakota49]

How much time passed between the “last” fill-up to the “next ride” when you noticed the the fuel level being lower? Also, do you fill the tank with the bike on the center, or side stand?
My thinking is that if you top off the tank with the bike on the side stand, then (in my experience) the tank isn’t filled as much as when it is filled on the center stand. Your bike is also older, with many miles, so it is possible that the tank filler’s gasket isn’t sealing as well as when it was newer after so many fill-ups and the rubber seal’s aging. So, it is possible that the combination of lower fuel level to start with and (possibly) several months of sitting with slow evaporation may be what contributes to your experience?
In any case, I wouldn’t be very concerned - there are no leaks, and no fuel in the oil either, so the issue is probably due to fuel evaporation.

Thank you for taking the time to answer. I'm sorry there are gaps in my info. I always fill on the side stand and have gotten pretty good at cramming extra gas in at that angle. I do realize that to properly fill you should be on the center stand or sit on the bike holding it level. I'm not very comfortable filling while sitting on the bike.
The interval between last fill and next ride was one day in both instances when the gas level was down. I will likely not be as concerned as I was previous to the oil analysis, but it is a bugger. Thanks again.

 

[SkooterG]

I have a Gen II, but I have always found the first bar to be quite variable. Your issue might have more to do with the gauge than anything else. I also find worse mileage in winter months due, in part, to winter blend gasoline. Last, but not least, I find short rides (especially in cool weather) yield abysmal mileage, especially if the bike is not fully warmed up.

I realize you are not new to FJRs or your bike in particular but I am not terribly surprised by what you reported. (I have a total of 300,000 miles on the two Gen II FJRs I have owned.)

I have over 400,000 miles on Gen I and 700,000 miles on all generations of FJRs and I have not found the Gen I fuel gauge to be variable at all. Nor have I ever experienced anything like the OP. So put me in the 'surprised' camp.

The poor guy has had his FJR for quite some time and miles so I am willing to believe he knows when there is an anomaly......

 

[Gen2Jockey]

Meh. Top it off with a gas can at home and see if it still experiences any loss. You're probably done mowing the lawn by that time of year anyway. ; )

 

[dakota49]

Good Idea. I can centerstand it in the garage and do that. I tend to limit my centerstanding. My technique is good having refined it over the past 60 years. However, with those yeas have come some sciatic problems that don't bother me much unless I start hoisting the FJR. Ha!

 

[Bounce]

Don't "hoist".

Hands on bars. Right grip brake engaged. Right hip to side of seat. Right foot on center stand and touch to make sure both feet are touching the ground. Stand Up onto the center stand; pushing the foot/stand into the ground. The bike will come up without the need to lift.

 

[dakota49]

Don't "hoist".

Hands on bars. Right grip brake engaged. Right hip to side of seat. Right foot on center stand and touch to make sure both feet are touching the ground. Stand Up onto the center stand; pushing the foot/stand into the ground. The bike will come up without the need to lift.

Yup thanks it's what I do. "Hoist" was just a figure of speech.

 

[Dan Cooper]

I side with Scooter on both of his assessments.
Dakota has been riding his scooter long enough to know when he has filled the tank consistently and knows how far it goes on that first fuel gauge bar and knows when there is an anomaly.
Depending on filling the tank to the bottom of the "well" inside the top of the tank or filling the tank to the brim, there is little difference between filling on the side stand or the center stand if the scooter is sitting at the same angle when filling. Just for reference, the tank holds about .7 gallons more fuel between the bottom of the "well" and the brim.

The fuel gauge will register fuel level differently if the key is switched on with the scooter on the side stand vs. while the scooter is upright or on the center stand. If the key is switched on with the scooter on the side stand, it takes several seconds/miles for the gauge to register the upright fuel level.

The Gen 1 fuel system is mechanically, functionally different from the Gen 2/3/4 fuel systems. The Gen 2/3/4 fuel system does not have a return fuel line from the fuel rail to the fuel pump.
The return fuel fitting on the Gen 1 fuel pump is snap fitted to the fuel pump housing and is sealed with an Oring that gets old and brittle (as Scooter mentioned). The original Orings have now been soaked in fuel for 20-25 years.
Ordinarily, the leak starts off as a very slow drip which lands on top of the engine and evaporates quickly and may not be noticeable at first, especially in warm weather and after a ride when the engine is still hot/warm.
In colder weather the drip may get faster when the Oring may contract a little, and drip on a cold engine overnight. The gas smell may or may not be noticeable depending on how well the garage is sealed up. But, one would probably notice the gas smell if the leak were .5 gallon overnight!!!

As an experiment slip a piece of paper under the gas tank overnight to see if there is a leak at the fuel pump return fitting or elsewhere.

dan

 

[dakota49]

As an experiment slip a piece of paper under the gas tank overnight to see if there is a leak at the fuel pump return fitting or elsewhere.

Thank you for such a thorough and knowledgeable reply. I will try your suggestion sometime later (probably in early spring). It's -10f here today and my garage is not heated. Ha!