Fuel Guage Accuracy

[RossKean]

Until very recently, my fuel guage has been quite accurate and very predictable. The first 8th and the last 8th were always fewer miles than the middle segments. The first 8th used to give me something like 20 miles and now is as few as 10. The last segment is now giving 10 to 15 miles before the flashing F. This isn't really a big deal but the kicker is that the "F" ALWAYS left a very predictablr 1.5 gallons in the tank which meant that I could reliably get another 60 miles if not pushing it.

Now, it seems like there is closer to 2 gallons left when it starts but this seems variable. If it can go one way, it might go the other. I hate to have to rely upon the trip meter as a guess for fillup time; especially on a trip.

Because it seems to be variable, I'm thinking its not the float and linkage but maybe I'm wrong. Seems to me that someone took one apart and there was some discussion on the circuit board contactors and the wiper? Can't find it.

Can this be refurbished or replaced separately from the fuel pump? Has anyone replaced one and at what cost? Metal on metal contact is certain to cause wear and or result in gunk buildup on the surfaces. Especially with high mileage (135000) and riding on less than perfect roads (in the Northeast). More constant movement with added fuel slosh.

 

[ionbeam]

Hi Ross! Since you are on the road I'll repost instead of linking to an old posting:

(Khunajawdge @ Mar 29 2009, 04:20 PM) <{POST_SNAPBACK}>
...Will be pulling the tank off soon. I'l try to clean any contacts that I find, but I'm heading into the unknown (again)?

Be careful cleaning the fuel level sending unit!!! This is what the unit looks like (photos by miikka555), the black squares are the actual resistive material and the silver is the conductive pickup contacts the float arm wiper connects to. Any abrasion to these two items will FUBAR the sender. You can carefully bend the arm that the float is attached to and adjust the sender level.

What bothers me is the sudden onset of your problem. There is a chance that a load of contaminated gas could have left a coating on the resistive material and/or the wiper on the float arm. I would suggest a tank of Techron before pulling the fuel pump assembly.

Another possibility is the float may have sprung a leak and now is a low rider in the tank.

Yet another possibility -- please take this one seriously, no kidding, in spite of how it is going to sound-- If your tank had a venting problem it can buckle. It may pull the bottom of the tank up, which you can only see if you pull the tank. Sometimes, from the top you can see the two indentations that run along each side of the tank are now deeper and run the entire length of the tank. This is unusual but not unheard of. I've seen a tank that this happened to. This will pull the pump up toward the top of the tank, causing a reading error and reduces the volume of the fuel tank.

If you do pull the pump assembly out, carefully inspect the resistor/silver conductor area looking for signs of wear or damage. In the end, the sender may simply have gone bad, again unusual but not unheard of.

Have you been following RadioHowies gas tank exploits caused by water in his tank?

 

[Fred W]

Ross, did your recent observation happen while riding on the slab vs. normal back roads? It seems like sometimes my gauge would report lower when riding a completely steady speed than when the fuel is being sloshed around regularly. Refilling a 1/2 gallon early is only ~20-25 miles anyway, so no real big deal there. And I always reset and use my trip meter as confirmation for when it is time to refill.

 

[Greenham]

I have never trusted any fuel gauge on a motorcycle. I had a HD Vrod that was notoriously 1/4 tank off. I like them I just wish they could figure out how to make them accurate. In the end after a few tank fulls and getting you avg MPG, ride by the odometer. I liked old school where you turned a valve from main to res when it started to sputter. then you KNEW how much was in the tank.

 

[RossKean]

The problem went away on three fillups today. Normal behavior now after about 5 tanks of odd and variable operation. At this point, I'll go for the crappy fuel theory. If it happens again, I will pull the sending unit. Not a tank venting issue I hope. I don't think that a collapsed tank would pop back.

Fred- I know what you mean but this was both slab and back roads.

I remember Howie's post. That was some pretty serious stuff.

 

[radiummadman]

fuel tanks are like women, ya gotta know how to read them !!!!!!!!!!

 

[RichDoyle]

I have never trusted any fuel gauge on a motorcycle. I had a HD Vrod that was notoriously 1/4 tank off. I like them I just wish they could figure out how to make them accurate. In the end after a few tank fulls and getting you avg MPG, ride by the odometer. I liked old school where you turned a valve from main to res when it started to sputter. then you KNEW how much was in the tank.

... Unless you forgot last time and have been unknowingly riding on reserve

Or you've got a BSA with a leaky on-off-reserve valve and you've been riding on reserve all this time

and with an odometer that free-spun, so you're at 38,000 miles in the morning and 56,000 miles by afternoon

I've had 5 bikes on the last 20+ years, all with fuel gauges and no reserve valve. They've all worked repeatably all the time. Of course, none were HD's, so there's that.

MPG can vary so drastically these days, the odometer-only doesn't really cut it. It is a good cross-check for the fuel gauge, though.

 

[RaYzerman19]

Could be the prolonged effects of that corn liquor they put in gas these days.... loosens gums but won't dissolve it. That and not going to name brand stations that may not have a good additive package..... as Alan says, the odd dose of Techron or Seafoam won't hurt, as the naptha in them tends to dissolve gums. Likely that all has accumulated over time.

 

[RossKean]

I think I will try the Techron enema. Not something that is likely to leave me stranded as long as I remember to use the trip odometer. It was fine again today. It can wait until I get home.

 

[RossKean]

Sorry, double post.