Improve Harley Fuel Mileage

The fuel mileage ratings established by Harley Davidson for their line of motorcycles, while accurate, is established under controlled conditions. In the real world – traffic, climate changes, two-up riding etc. all affect average fuel economy. A 2006 883 Sportster was used for this test. Harley list fuel mileage for the 2006 Sportster at 48/55 mpg. Prior to trying to improve the fuel economy of my Harley, I was averaging just over 51 mpg.

Three primary changes were introduced during this test to improve fuel economy. The accompanying mileage chart shows where each change was introduced.

  1. Install Sreamin’ Eagle “splitfire” sparkplugs.
  2. Replace the air filter
  3. Change from standard HD motor oil to HD synthetic motor oil

Splitfire Spark Plugs

Most of this test to improve fuel mileage was conducted during my daily commute of just under 80 miles round trip. Typically I take the back roads to work, where I average about 40 mph. On the return trip I will take the Interstate, where the average speed is about 60 mph. Ambient temperatures ranged from in the 50’s to 80’s over the course of this test, with the average temperatures in the range of 65-75 degrees. Mileage listed over 80 miles was likely two-up riding, including three mileage readings from the commute to the Laconia Motorcycle Rally.

 Gallons……….Mileage……….MPG
1.41…………….74.8……………53.04
1.45…………….75.3……………51.93Screaming Eagle Spark Plugs
1.39…………….75.0……………53.95
1.39…………….77.8……………55.97
1.41…………….80.5……………57.09
1.36…………….75.2……………55.29
1.56…………….79.0……………50.64
2.63……………137.7……………52.35
1.44…………….72.0……………50.00
2.02……………111.1……………55.00
1.60…………….85.8…………… 53.52      * Splitfire Spark Plug Averages

Air Filter

Not only did the fuel economy on my Harley Davidson improve by two miles per gallon by installing the Screamin’ Eagle spark plugs, but I also noticed an improvement in performance at the ‘shift points’. For example, to help maximize fuel economy, I shift into 5th gear about 41mph. Prior to installing the Screamin’ Eagle spark plugs, this was the bare minimum speed for holding 5th gear. Any drop below that mark and the carburetor Sportster would buck in protest. With the Screamin’ Eagle Splitfire plugs installed, I can let the motorcycle slip down to 37 mph in fifth gear before it would buck in protest.

Gallons……….Mileage……….MPG
2.25……………127.3……………56.57
1.26…………….75.1……………59.60
1.69…………….93.6……………55.38
1.75……………100.9……………57.65
1.88…………….99.0……………52.65
1.40…………….83.1……………59.35
2.05……………117.5……………57.31
1.75…………….99.5…………… 56.93           * New Air filter and Blow-by repair Averages

A couple of things are interesting to note here. First, the blow-by repair, which pushed more of the blow-by oil into the mouth of the carburetor did not produce a negative effect on the fuel economy of the Sportster. Second, despite cleaning the air filter multiple times as outlined in the Harley Davidson owners manual, installing a new air filter at the 10k maintenance mark produced a significant increase in the fuel mileage of the Harley. Moving forward, it is my plan to replace the air filter at 10k intervals. The increase in fuel economy will make replacing the Sportster air filter at these intervals pay for itself in short order.

Synthetic Motor Oil

Gallons……….Mileage……….MPG
1.58…………….89.6……………56.70
1.54…………….80.8……………52.46
1.40…………….78.3……………55.92
1.40…………….77.1……………55.07
1.37…………….74.8……………54.59
1.45…………….78.8……………54.34
1.55…………….87.9……………56.70
1.40…………….77.2……………55.14
1.44…………….78.7……………54.65
1.45…………….80.35……………55.06* Synthetic Motor Oil Averages

I put Screamin’ Eagle synthetic motor oil in the Sportster at 12,500 miles. The main reason for switching was that synthetic motor oil for air cooled engines is supposed to help them run cooler. With summer approaching, I wanted to lower the operating temperature of the Evolution engine. The synthetic motor oil produced no increases in fuel economy, and I would contribute the slight drop in fuel mileage to an air filter that is starting to get dirty again plus and increase in foul weather riding during the last stretch of this test.

The final numbers for this test had the average fuel mileage at 54.93 mpg, an increase of almost four miles per gallon. This average would continue to increase over time if I continued tracking miles, my guess would be to about the 56 mpg range. With an average price per gallon of $4.03 over the test period, the increase of four miles per gallon immediately saved me $16.12 – more than the price of the Screamin’ Eagle spark plugs. When you factor the cost of a stock air filter into the mix, the air filter and spark plugs pay for themselves in short order with increased fuel economy.