Usability Assessment Test of Starting a
Two-Stroke Engine
Shaun Eiler
3/5/03
Usability Test
Two-stroke engines have many different uses. They are used in weed-eaters, leaf blowers, chain saws, and many different machines. The particular two-stroke engine being tested; is on a 2000 Yamaha Blaster. The Yamaha Blaster has a quick revving 195cc two-stroke engine (Yamaha-motors online). The goal of this test is to see if starting the machine is user-friendly. It may be difficult because this particular machine uses a kick-starter. A kick-starter is a lever on the side of the engine, that a person must start by using their right leg. Standing up is the best way to do it, because more body weight and leverage can be put into it. A two-stroke engine uses a mixture of gas and oil. It takes a bigger spark to ignite the fuel, therefore, a kick-starter must be used on this machine.
The participants were all greeted and debriefed on the tasks and the main goal that they were supposed to accomplish. Each participant agreed to the test and understood the steps they were to follow in this test. There were five tasks the participants are going to try and accomplish. Task #1 is to make sure the fuel line is on. Task #2 is to make sure the key is in the "on" position. Task #3 is to set the engine kill switch to "run". Since it is February, the climate is cold, and therefore the choke needs to be pulled all the way out. This is task #4, to pull the choke out. Task #5 is also the main goal of this test; to start the engine.
Observation will be the main source of information. A brief interview will occur after the participant has finished their testing. All testing will occur in my garage. Only the test subject attempting to start the engine and the observer, will be the only ones in the garage. All other subjects were to remain in the house. Once a participant has finished their testing, they will be sent to another location where they will not come in contact with any participants who have not tested yet.
The participants in this test will include three males and two females. The subjects' names will remain anonymous, and they will be called test subject #1-#5. Test subject #1 is a forty-five year old male weighing two hundred pounds. Test subject #2 is a twenty-two year old male weighing one hundred and seventy three pounds. Test subject #3 is an eighteen year old male weighing one hundred eighty pounds. Test subject #4 is a twenty-one year old female weighing one hundred twenty pounds. Test subject #5 is a forty-three year old female weighing one hundred five pounds. The weight of the participants is listed only because it will play a factor in this test.
Test subject #1 has had a lot of experience with two-stoke engines. Therefore, he will be the expert of the group. Test subject #2 has had some experience but not quite as much as test subject #1. Test subjects #3-#5 have had no previous experience of any type with this particular engine.
Test subject #1 has had a lot of experience with engines, therefore, he knew exactly what to do. Test subject #1 started off by turning the key on, and then he set the engine kill switch to "run". Next, he turned the fuel line on and pulled the choke out. Test subject #1 did not do the tasks in the order he was told to, but since he accomplished the main goal it was be overlooked. Finally, he pulled the kick-start lever out. It took five kicks before the engine fired up. Since test subject #1 was able to start the engine easily and quickly, this got the usability test off to a good start. When asked why he was able to start the engine so easily, test subject #1 stated that experience helped him know what to do.
Test subject #1 was sent to the other garage, and test subject #2 entered the test area. Test subject #2 started off by turning the fuel line on. Next, he turned the key on and pulled the choke out. He then pulled the kick-start lever out and proceeded to try and start the engine. After about ten kicks, he started to get frustrated. He was confused and oblivious to why the engine was not starting. Test subject #2 then calmed down and began to retrace his steps. He checked the fuel line and the key, and then he noticed that he had forgotten to turn the engine kill switch to "run". After he did this, he attempted to start the engine once more. After two kicks, the engine started. Test subject #2 stated that he thought he knew what he was doing, therefore, he didn't listen closely to the directions. He thought he knew enough about engines to get him by. He also said he would have been able to do it if he would have paid attention at the briefing.
Test subject #2 left, and test subject #3 was asked to begin his testing. Test subject #3 started off by turning on the key. Next, he turned the engine kill switch to "run". Then he tried to start the engine. Since he had not turned the fuel line on, the engine would not start. When test subject #3 could not get the engine started, he got frustrated and quit. He was told of the mistake he made, and so he went back and turned on the fuel line. Next, he once again attempted to start the engine. After two kicks the engine started up. Test subject #3 forgot another step when he failed to pull out the choke. Since the engine was warmed up from the previous test subjects, it still started even though the choke was not pulled out. When asked what he thought about the ease of starting of this machine, test subject #3 replied that it was too much work and too much to memorize. He felt it should be much easier so that way a person can get on it and go, and not have to worry about following all these steps.
Test subject #3 left, and it was test subject #4 that was to begin her testing. Test subject #4 started off by turning the key on. Next, she turned the engine kill switch to "run". She proceeded to look for the choke but could not find it. She finally gave up looking and was going to quit the test. Test subject #4 was then shown where the choke was so she could continue the test. Once the choke was out, she found the fuel line switch and turned it on. She then pulled the kick-start lever out and attempted to start the engine. Three kicks was all that she could handle. Her leg was not strong enough to do any more, therefore, she got frustrated and quit. When asked what she felt about the starting of this machine, test subject #4 stated that it was confusing and she was not strong enough to do it. She felt as though she might be able to get it started every now and then, but it is not something that she would want to go through every time she wanted to ride.
Test subject #4 completed her testing and left so that test subject #5 could enter the test area. Test subject #5 started off by turning the key on. Next, she turned the engine kill switch to "run". After she completed these two steps, she became totally confused on what to do next. She had a hard time remembering what the other tasks were that she was supposed to complete. The more test subject #5 tried to remember her next move; the more flustered she became. Test subject #5 got to the point where she quit the testing. Since it is crucial to the test that she finish, test subject #5 was informed of how to get to the final task. Her last task was to start the engine. Test subject #5 could not even push the kick-start lever down with her leg, she was too small and not strong enough. When asked how she felt about the ease of starting on this machine, test subject #5 stated that she would never purchase a machine that had a kick-starter. She stated that she would much rather have a machine that had an electric start, because even someone her size would then be able to start the engine. Since two-stroke engines do not have electric start, then this means she would have to go to a four-stroke instead.
Two of the five participants were able to get the engine started. Of these two, only one was able to complete the steps without any hindrances. Test subject #1 was the expert coming into the test, his results showed that he in-fact knew what he was doing. Test subject #2 had somewhat of an idea, but he failed to listen to all the instructions. Therefore, he did not do as well as he could have. The final three participants had more problems with this test, some more then others. Test subject #3 and #4 had problems because they have not had any experience. Test subject #5 was hindered by her size, and she was not able to start the machine.
After all the testing had been done, the test subjects were thanked for their participation and told that all their information would be kept confidential. Two-stroke engines are for serious riders who have had plenty of experience. Besides the difficulty level of starting them; they are also more powerful and high-revving then a four-stroke.
For the most part, the participants showed that after a rider became accustomed to the starting procedures; they would be able to start the engine without any problems. Turning the key on, turning the fuel line on, setting the engine kill switch to "run", and pulling the choke out are basically all memorization steps. The main area of problem that one should be concerned about is the actual starting of the engine. A kick-start lever has to be kicked with a lot of force to be able to start the engine, therefore, someone with a strong leg would only be able to start this particular machine. A smaller individual or a female would have a harder time starting the engine then what a large individual or a male would.
There are several recommendations that would make starting this machine easier. The first one is to put a label by the choke, and make a better one for the fuel line switch. For someone who has no experience, it would be very difficult for them to even be able to find the choke. There is nothing anywhere around it that says "choke". Also, the labels on the fuel line switch are engraved into the metal. This is fine, but they are very small, and after years of riding they will be ground down or rust will cover them. If the machine was bought new, then the owner will not have any troubles learning how to operate the fuel line switch. If the machine is bought used, then this is where the rust and other problems come into play. Somehow the labels need to be made permanent so they will always be visible. As far as the kick-start process goes, there is only one recommendation that could make it easier. If a longer kick-start lever was installed, then it would allow the rider to put more leverage into starting it. This would allow smaller riders to be able to start this machine with more ease.
Nielsen, J. (1993). Usability Engineering. San Diego, San Francisco, New York,
Boston, London, Sydney, and Tokyo: Morgan Kaufman.
Rubin, J. (1994). Handbook of Usability Testing. New York, Chichester, Brisbane,
Toronto, and Singapore: John Wiley & Sons, INC.
(2003). http://www.yamaha-motor.com/products/unitinfo.asp?lid=1&lc=atv&cid=1&mid=47
Retrieved February 25, 2003, from the world wide web.
*All other information was found from interviews with the participants*