Hummm . . . maybe you should start with the engine already hot so to make the test go faster and eliminate any other variables. This way you run it dry on one fuel and refill with the next and start with a hot engine. This will allow you to run more tests more quickly and perhaps repeat the test for more accurate readings as well as in case the engine changes operation from test to test. Will also allow testing with additives as well. You may want to run a funnel for a gas tank instead of the regular tank so you can see the fuel used to the last drop and add it more easily or even a long clear hose to watch the fuel being used.