I've learned over the past few days that my trike's fuel tank apparently needs good "burping" in order to actually "fill", to a HOPEFULLY CONSISTENT level at gas starion fill-ups. I don't know WHY it sometimes refills to different levels, but have proven to myself that it does.

In one recent test fill-up, the tank appeared to be full right to the tooth tips of the "toothed ring" in the filler tube. I then rode it from the gas station to my home 1.4 km away. The next day, with the trike not having been ridden, I checked the fuel level again. It was low enough that I started adding fuel from a gas can using a measuring cup. On my first attempt, it took 4 ounces. I decided to wait and see if the level fell. It did. I added another 4 ounces. The level fell again, Suspicious, I checked the floor under the trike. No leak. I repeated this process, and ultimately got 22 ounces into the "full" tank. That's 0.69 of a quart. The next day after, I checked again. I got another 2 ounces into the tank.

So, my gas station fill-up was actually 24 ounces = 3/4 of a quart short of a full, accurate fill-up.

This might at least partially explain why the HD Info screen MPG claim sometimes differs from what a manual fill-up seems to say.

I do have a DK Custom one inch tank lift on my trike (in an effort to get more air to the cylinder heads and to make cleaning them easier). This obivously lifted the FRONT of the fuel tnak by about one inch. I did NOT install the REAR lift.

Does anyone know FOR SURE (based on doing, not just a guess):

1. Does a tank lift increase or decrease the need for burping the fuel tank, when trying to get ACCURATE comparisons between the HD Trip Info screen MPG claim and the manual-fill claim?

2. How are you supposed to effectively burp a TRIKE, since you cannot simply tilt it to the right and left like you can a 2-wheeler?

3. How can you be SURE the tank is really "full" (say, to the tooth tips of the toothed ring), CONSISTENTLY EVERY time, even when adding gas a few ounces at a time?

4. Does a Harley "6 gallon / 22.7 liter" fuel tank hold that capacity when filled "unburped" or "burped"?

Those of you who scoff at anyone doing any fuel mileage investigation, please don't clog this thread with sarcastic comments. I know all about "stop testing and just refill when low and enjoy the ride". That's great most of the time. But right now, I'd like to know why my HD Trip Info screen apparently sometimes disagrees with manual fill-up results, and NOT by a consistent percentage, while the 'Range" prediction from the onboard system agrees pretty precisely with the Trip Info screen. "Inquiirng minds need to know . . . "

Jim G

 

Your are over filling it.

 

While you can’t shift hard left and right, you CAN wiggle the bars enough to “burp” the tank and get another quart or so in the tank.
1” front & 1/2@ rear tank lift installed.

 

Can you explain? Do you mean that some of it is "above" the "full" fuel level? If so, what happens to it? Does it get somehow ejected? Does it somehow plug a vent? Or?

Jim G

 

Very interesting, ShovelEd. So, wiggling the bars is enough to burp it. Good to know. And, I see your "net" tilt is only 1/2" (1" at front minus 1/2" due to rear lift).Did you notice any change in the amount you could add this way after installing the tank lift?

Jim G

 

No noticeable difference.
But I DID add 4.9 gallons (burping) on a recent fillup.
Low Fuel light not on, display showing 31 miles left until empty.
I believe the light activates at 25 miles.

 

An interesting add-on development: I rode the trike just 71 km yesterday, which I view as way too short to measure MPG because of the error potential in any manual filling due to the burping having an exaggerated effect on smaller top-offs. But after that ride, I topped the tank up again via manual filling ONLY from the gas can, and then measured how much fuel I was able to add. It was 3.33 liters. That calculates out to 3.33/71*100 = 4.69 Liters / US gallon. The HD Trip Info screen showed 3.16 liters consumed, and 4.4 liters / US gallon. That's a 6.7% difference.

But this morning, I chekce dthe fuel level again. It had dropped again overnight, but only took 2 ounces to get it back to the tips of the teeth in the filler. So, yesterday's manual refilling, even though done without any wiggling of the bars, seems to have reduced the amount of "settling" overnight.

Next time, I will try the wiggling of the handlebar. For those that wonder how wiggling the handlebar on a 3-wheeled vehicle that weighs 60 lb can possibly do much, it's likely the COMBINATION of the physical wiggling PLUS the change in front end elevation when you turn the handlebar to either the left or right stops. This is because of the rake and trail built into any trike or 2-wheeled motorcycle.

Jim G

 

Do you jam the fuel filler nozzle into your tank up to the (fork gaiter shaped) vapor recovery seal? On my Sportster (not a TG) I manually hold the vapor seal back enough to allow fuel flow, and I can see how full my tank gets without it spurting out due to overfill.

Also, on my trip to Wyoming last summer (in my truck), I found several gas pumps that shut off early, and one that did not shut off until gas was gushing from the tank. So, you may want to factor in the possible inaccuracy in the gas station pumps themselves. Not saying they measure inaccurately, just that they may not all fill to the same point before they shut off. I realized one pump shut off about 2 gallons short of fuel when I noticed my fuel gauge dropping sooner than it should after a fill up.

I don't know if you even have gas nozzles similar to those used in Kalifornia, but if you do maybe try to fill it by holding the vapor seal back enough to allow flow, and fill it visually. You can also push up and down on the handlebars to rock the tank a bit, but I'm not sure where any hidden air pockets would be on a tank that is lifted, and sets level naturally, not leaning like my bike on a kickstand.

You do realize that gasoline expands and contracts much more than water does due to temperature? Have you taken that variable into your calculations?

John

 

The implication of that is that you had 6 more miles available until the fuel light would come on. Let's assume for a moment that your MPG is, say roughly, 35. Then 6 miles would consume 6/35 = 0.17 gallon. You got 4.9 gallons into the tank, via burping. So, if you had waited until the fuel light came on, you would have been able to add roughly 4.9 +0.17 = 5.07 gallons. That implies that the light comes on at "about" 1 gallon left in the tank. Useful to know.

Jim G

 

John, if your question was directed to me, no, we dot have those vapor seals (some call them "condoms") here in the Province of Alberta in Canada, nor in The Province of British Columbia where I lived for a while. So, I can clearly see when the fuel level is approaching the tips of the teeth on that toothed disc in the filler neck. And yes, I do agree that different gas pumps, even at the same gas station, seem to shut off at different fill levels even when controlled manually the same exact way. That, coupled with the presence of the burping issue, greatly increases the error potential, and especially when the total distance traveled between fill-ups is small enough to exaggerate even a smaller error. That's why I am reluctant to trust EITHER the gas pump nozzle or my human technique for short distances ridden.

In fact, I HAVE noticed that my MPG results look the most reasonable when the distance bewteen fill-ups is 300 km versus 75 km for example. For the same error in manual fill level, the 75km ride will naturally look 4 times worse.

Fortunatyely, I have not seen the ambient temperature change enough t have an effect on gasoline volume changes versus temperature. The bike is stored in a large well insulated garage UNDER the highest level of our home (Canadian building code REQUIRES great insulation), and the temperature inside the garage has varied by a MAX of 10 degrees C even at night, and I always take my measurements in the daylight. The difference in temp at the actual times of checking the fuel level has not yet been more than a maximum of 2 or 3 degrees C = 4 to 6 degrees F. Could that small a maximum change make a meaningful volume diffference in the gasoline?

Jim G