That could easily be due to temperature change. Filling up on hot day over a hot engine, and then checking in the morning when all is dead cold?

John

 

The "hot engine" comment is a good one. When, before this testing period, I was filling up at the gas station, this would certainly be a potential factor. The gas coming from the gas station tanks would always be a similar moderate temperature, but the gas still in the trike's fuel tank after a ride would certainly be hotter. But to avoid possibility of a fire, I have been topping up manually inside the garage AFTER the engine has been cold for a while (at least a few hours). Goven what you said, I am going to really pay attention when I refill at the gas station, and be sure to wait a few hours afterwards before topping up manually in my garage. Good catch.

Jim G

 

Since you're chasing ounces, that might account for at least a few. Glad I could contribute to your research.

John

 

The station’s tanks location “underground”, should indicate fuel temp cooler than ambient.

 

Yes, which would theoretically reduced the temperature of the "hotter' gasoline in the trike's fuel tank. But the amount of cooling effect would depend upon how MUCH gas is put in from the cooler gas station tank into the 6 gallon trike tank. If only 3/4 of a gallon (because the ride was short) the effect would be very small. But if 5 gallons is added, the effect would be much greater. Another variable that is hard-to-control and to predict or measure.

Jim G

 

Which is why some of us don’t go “down the rabbit hole” of statistics, and just ride.

 

Fuel tank needs expansion room. Also over filling can cause venting issues. Just like your car over filling is not a recommended practice.

If you have to rock it to get fuel in it was already full.

 

Yes, and you are measuring by volume, not weight. With 6 gallons, even a full tank sitting out in the sun is going to need somewhere for the gas (and vapors) to expand. The one-way vapor valve and charcoal can capture those vapors for later burning. Otherwise, your tank would burst from pressure alone. The gas cap only vents inward, not out.

John

 

Good points. How much "unused' vaolume is required? Is it too high if the fuel touches the tips of the teeth in the toothed ring inside the filler? If so, is there another easy-to-see reference point in the neck of the tnak?

The ideal reference point would be one that also ensures that there is no place in the tnak's shape that can create an air bubble that artificially inflates the apparent height of the fuel level. But it also has to be visible when filling the tank at the gas station.

Jim G

 

I would think filling to the bottom of the "toothed ring" would be fine, and something the engineers hopefully considered.

John