Fuel capacity, filtration, and sputtering - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 04-29-2010, 01:36 PM Thread Starter
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Fuel capacity, filtration, and sputtering

I am confused. According to the Owners Manual the capacity of the fuel tank is supposed to be 3.57 US gallons. I can never put nearly that much in it. When the gauge reads nearly empty I fill it and it's seldom over 2.1 gallons unless the gas extends up into the filler neck, which is to be avoided because it will sure as heck dribble out and over the tank as soon as the filler cap is closed and the sun hits the tank. I have occasionally had to switch to reserve while riding. The manual says there is an extra 0.6 gallons or so remaining when you do this, but upon filling I never put more than about 2.5 gallons into the tank. So do I have a gallon of sediment in the tank (har)? Doubtful because this is a clean 2003....So where is this extra capacity?

On another note, the other day I had the engine cough to a stop. Temp was around 75 degrees and sunny so no problem there. The petcock was "on" as I usually leave it. I switched to reserve and waited. In the past this has solved the issue although it takes a little while for the gas to dribble down and refill the carb bowls, but this time I had no action on the reserve after at least 5 minutes. I pushed the damn bike a mile or so to a gas station and it took....2.3 gallons. It could not have been empty or even to the reserve level. With the petcock back to "on" it started and ran fine. So what happened to my reserve fuel?

Is there a fuel filter someplace that I can't find that might be plugged? Is it likely that the reserve inlet in the tank is plugged? Could I be experiencing the phantom out-of-gas syndrome due to vacuum building up in the tank? If so where do the tank vent hoses exit so I can check if they are plugged -- I have never been able to trace them in the bowels of the bike.

2003
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post #2 of 9 (permalink) Old 04-29-2010, 02:09 PM
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I can't answer your questions but can compare to my 2003. I ran out of gas in the ON position. I put it to RES and drove directly to gas station 2.5 miles away. I was able to put 3 gallons in there. But I did this on purpose when I first got the bike to see roughly how many miles per tank I can get.


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post #3 of 9 (permalink) Old 04-29-2010, 02:45 PM
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The reserve portion of your gas tank is but a name, nothing more. The petcock has two tubes on it going up into the tank. One is shorter than the other. On your bike, your petcock is always driven by vacuum, whether set to ON or RES. So, sitting and waiting for gas to dribble with the bike turned off is a waste of time with this petcock. It only opens when vacuum is applied. The twin tubes in the petcock sit similar to this (il) where the little letter i is the short tube and the letter l is the long tube. In the ON position, the gas is being drawn from the long tube, and when in RES, from the short tube, giving you the "reserve" fuel. All bikes are different, as all vn750s are different. Depending on your fuel mileage and how full you fill your tank, you might get 120 miles before being forced to switch to reserve, where someone else might need to switch at 110, or 140 miles. Driving habits, weight and how well your bike is running all help determine how far you can go.

I would check your mpg over the next maybe three tanks of gas and that will give you some idea of what is going on. The filter is a screen around the tubes in your petcock, unless someone has installed inline filters on your fuel lines leading from the petcock to the carbs. If you wanted to, you could remove your tank and petcock to check the screen and such, and if you did that I would take that opportunity to flush your tank clean. If the filter and tank are already clean, it won't make any difference.

The fuel gauge is another thing that will read different on every bike. Use it as an estimation, not the gospel. It will start out reading full for the longest time, as your tank is larger at the top, but once the gas gets down into the lower part of the tank, you seem to be able to watch the gauge move while you ride! Not quite, but it feels like it.

Once you know what your average fuel mileage is, then I would ride the bike and intentionally run out of gas in the ON position of the petcock, switch to reserve and then go get her filled back up, then keep the amount of miles you got before running out as your rule of thumb. I'm sure you are resetting your trip meter on the odometer every fill up, right? That number will be a far greater indicator than the fuel gauge. By the way, you should familiarize yourself with where the petcock is located so you can switch to reserve while the bike is still running instead of running the carbs dry before switching over. It can be done pretty smoothly if you practice it on a lonely road a few times. It helps to do this because you still have vacuum applied and the carb bowls will fill more rapidly, keeping you going. When I first got my 1500 I was on a 4 lane road, passing a semi when my bike started studdering. I was able to move it to reserve and continue on without hardly slowing down, although I would have chosen a more remote location to try that the first time!

I typically start leaning toward a gas station at 100 miles on the trip meter, just out of habit.

Fergy
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post #4 of 9 (permalink) Old 04-29-2010, 03:06 PM
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Great write-up Fergy!
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post #5 of 9 (permalink) Old 04-29-2010, 04:42 PM
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Chavismo`s mileage test is a practical one we should all perform with our own bikes, IMHO.
I would also suggest making note of how far you have gone when the fuel gauge reads 3/4, 1/2 and 1/4 full tank as well. Then if you forget to reset the trip meter when you fill the tank, the gauge will give you a better estimate of how far you can still go.

sgsibob points out a problem that should have been checked for, before the reserve fuel setting was needed. When he switched to reserve and the engine would not start, he did not know if it would run in that position even with a full tank. So he is left wondering if the pick-up is broken or plugged, and pushes the bike a mile to get gas. Next time you get gas, switch onto reserve for a few miles to ensure you know it will work when you need it.

The only fuel filter (unless added by a previous owner) is the screen in the body of the petcock that sticks up into the tank. I am guessing on this, but I suppose the screen could be plugged only at the bottom where the reserve pick-up would be positioned. It may be worthwhile to remove the tank to check and clean or rebuild the petcock and fuel pick-ups.

sgsibob, if you suspect the Phantom OOG Syndrome, open the gas cap to relieve the vacuum. There is a very small vent or breather between the mounting screws which can get plugged up. Take the cap off the tank and clean the vent out, or drill it just slightly bigger.

There is also a vent hose at the back of the fuel tank that hangs down a few inches below the frame. If there are two, it should be the left side one I believe. To determine if it is blocked, try snaking the bottom of the hose up and out, then blowing into the hose to see if you can hear air coming through the vent under the fuel cap.

Edit: I seem to be reiterating a lot of what fergy said because I was interrupted halfway through writing this post. I hope it has enough differences to warrant leaving it here.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
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July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


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Last edited by OlHossCanada; 05-06-2010 at 01:55 PM.
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post #6 of 9 (permalink) Old 04-29-2010, 07:13 PM
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Quote:
Originally Posted by sgsibob View Post
....

On another note, the other day I had the engine cough to a stop. Temp was around 75 degrees and sunny so no problem there. The petcock was "on" as I usually leave it. I switched to reserve and waited. In the past this has solved the issue although it takes a little while for the gas to dribble down and refill the carb bowls, but this time I had no action on the reserve after at least 5 minutes. I pushed the damn bike a mile or so to a gas station and it took....2.3 gallons. It could not have been empty or even to the reserve level. With the petcock back to "on" it started and ran fine. So what happened to my reserve fuel?
.....
This sounds like the 'phantom out of gas' syndrome (POOGS). Happened to my '06 last month, twice. Happens to a lot of VN750 based on this forum. If it happens to you again (mine was consistent when the gas gauge hit 1/2 tank), simply open the gas cap, wait a few minutes and try to restart the engine. If it restarts, chances are it is due to POOGS. Solution is to clean the gas cap vent tube and gas cap vent. Spray carb cleaner down the vent until it runs clear (you'll see dripping in front of the rear wheel) and disassemble and clean the vent located under the gas cap. The process only takes a few minutes. I'm going to clean the gas vent tube every year to prevent dirt from reaching the vent in the future.


Chris Glennon - Portland, OR
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post #7 of 9 (permalink) Old 04-29-2010, 08:16 PM Thread Starter
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Thanks everyone for the honest replies. At least now I know not to hunt for a fuel filter. As I said I have used the reserve before so I know how it works -- this is why I was so surprised that the bike would not start this particular time on reserve -- it has in the past. I have no problems with the vent in the fuel cap, as I have had it apart and rebuilt it before (see my other posts....) I do reset the odometer at every fillup and usually get 100-110 miles before it's pretty empty. I had 90 on it this time. It might have been POOGS which affected me one time before when at high elevation (but never again at the same elevation), but I doubt it. I think I will check to be sure there is no leakage of vacuum at the petcock.

I am still wondering though about the difference between my experience and the stated tank capacity.

2003
Chrome crash bar
Mustang seat
LeatherLike hard bags
Sissy Bar riser
Memphis Shades Malibu shield
in gradient black
7K as of 6/08
Paid for with the
Rebel 450 above
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post #8 of 9 (permalink) Old 04-29-2010, 10:20 PM
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I`m not sure why your bike`s fuel capacity would be so much less than specified. When mine was empty and running on reserve it took from 11-13 liters which is about 3 to 3.4 US gallons. The only thing that comes to mind for determining your tanks true capacity is strapping a full 1 gallon tank to your luggage rack and riding on reserve until it quits. Pour in the gallon and head for the nearest service station to fill up.

Gordon

1991 VN 750 -"Cosmic Lady" or "Bad Girl"?
Purchased May 16, 2008
Approx.19,300km (12,000 miles)

H-D windshield
Relocated R/R
MF-AGM battery
Fiamm Freeway Blaster horns
F&S luggage rack and engine guard
Kury Offset Hiway pegs
July 13, 2016, Riding on the DARKSIDE now, Classic Radial 165/80-15


TOP TEN THINGS A NEW RIDER/OWNER SHOULD DO. Click on link.
https://www.vn750.com/forum/showthread.php?t=9127
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post #9 of 9 (permalink) Old 05-05-2010, 10:28 PM
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I think the .6 gallons of reserve is part of the 3.57 gallons. I always run my bike until I have to switch it to reserve and it only takes about 2.75 gallons to fill it back up. I'm averaging 40mpg.

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Currently 20,147 miles (5/1/2010)
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