Start enrichment

This value will help an engine to stabilize after starting. This amount will be added to the injector time after the engine is started and reaches 500 RPM. It will then be phased out in a couple of revolutions. This value is also compensated with the water temperature %, and is not active in Expert mode. Then the Water Temperature graph is used. The value is set in milliseconds. In Expert mode this value for Start Enrichment will be blanked out and the graph value for that temperature interval will be used. See the graph sample below.

Maximum fueling

This setting is to protect against over fueling from all the graphs with accelerator pumps etc. It will limit the final injection time to this value if it is higher. This value can be calculated as the time it takes 1 revolution for 2-stroke engines, or 2 revolutions for 4-stroke engines. The calculation for 4 stroke engines at 7000RPM is seconds=60 * 2 / Max RPM=120/7000 = 0.017 = 17 milliseconds. For a 2 stroke it at 7000RPM is seconds=60 / Max RPM = 60/7000 = 0.085 = 8.5 milliseconds. The recommended injector time is 85% of that value which results in 14 and 7 milliseconds respectably. If your duty cycle of the injectors at full load max RPM reaches over 85% you may have to go for larger injectors or increase the fuel pressure to maximum safe pressures. On the Fuel Matrix this will also prevents the tuner from selecting higher values there. This value is set in milliseconds.

Start prime pulse

This setting is to assist in the starting of the engine. When the engine starts to crank and reaches 100 RPM a set amount of fuel is injected on all the injectors to get the first one with spark to ignite and turn the engine. A colder engine requires more initial fuel to start. This value is also compensated with the water temperature and is not active in Expert mode. Then the Water Temperature graph takes over this value. In Expert mode this value for Start Prime pulse will be blanked out and the graph value for that temperature interval will be used. Note that this value is x10 so 6.4 is 64 milliseconds. See the graph sample below.

The Spitronics ECU’s have a manual prime function where you can press the accelerator pedal before starting to inject fuel in the system. This fuel is measured at 50% of the start prime pulse setting. It is injected each time the throttle is pressed more than 25 % opening.

Should the engine be flooded, you may keep the pedal fully pressed to the floor during cranking. This will indicate the ECU to cut injectors and only provide spark. Press the throttle in all the way before putting the ignition on. It will prevent the prime pulse from injecting more fuel when the pedal is pressed. Once the engine starts release the pedal and then injection will commence as normal.

Vacuum fuel cut off & RPM fuel cut off

This feature is useful in town and downhill driving and will save fuel. It will let the engine run against compression as you are decelerating. It will also prevent flaming in the exhaust during accelerator blip. Injectors will be cut when the MAP sensor value is below the vacuum setting and the engine RPM is above the RPM setting. There is a dead band feature built into these settings to prevent jerking when cruising close to the parameters. If you feel a jerk when the feature is activated or deactivated, adjust these settings till it changes over smoothly. This is normally where the change from positive to negative drive on the prop shaft is.

Injection teeth

This feature adjusts the start injection degrees. It is only available on gear type triggers as low as 12 teeth per revolution. Normal injection timing starts just after the intake valve closes. The warm valve helps atomizing the fuel and makes the engine use less fuel. Put the engine on the degrees where you want to start injection. Count the number of teeth from the slot or missing teeth in the gear, in an anti-clockwise direction, to the sensor. If the pickup is in the slot imagine the tooth there and count it as well. Even if it is 60. The firmware will move injection in the slot to the closest teeth as this is not as critical as spark timing. You may change this value during tuning to see if you get better atomization and performance increase. Usually this is best seen at idle. Find the spot where it runs rich and make idling leaner. Start with low teeth and move to larger numbers to see when the valve closes. It will go rich at that point.

TPS Gain

This setting will adjust the rate at which the TPS sensor will move the MAP bar to the right of the graph during Graph Map + TPS calculation mode. This will simulate a MAP signal and the gain adjustment will produce the right amount of fuel during pull-off. (For further details see the tuning section).