FAQ
Q. What is Sam's Servo Sub?
A. It is an electronic circuit that is used in place of the EXUP servomotor assembly.
Q. What does it do?
A. It electronically simulates the servomotor assembly precisely and 'fools' the Ignitor Unit (black box) into 'thinking' the servomotor assembly is electrically connected to it.
Q. Why would I want to replace and simulate the EXUP servomotor assembly?
A. Sam's Servo Sub is intended for use by those that have replaced their stock exhaust system with an aftermarket 'full' system. With the stock exhaust system gone, the servomotor assembly serves no purpose; it is deadweight. Sam's Servo Sub is a lightweight replacement for the servomotor assembly.
Q. Rather than replace the servomotor assembly with Sam's Servo Sub, couldn't I just simply disconnect and remove the servomotor assembly and be done with it?
A. Yes you can. The down side to this is that when the Ignitor Unit senses the servomotor assembly missing, it generates a 'tach diagnostic' of the form that causes the tach needle to 'jump' between actual engine rpm, then to zero rpm, then 7000 rpm and repeat this sequence continuously. This tach diagnostic has appropriately been termed as the 'Tach Tango'.
Q. So if a person has already replaced their stock exhaust system with an aftermarket 'full' system and also removed their servomotor assembly, the fitment of Sam's Servo Sub eliminates the 'Tach Tango' and that's all, correct?
A. Yes and no. The statement is correct in terms of functionality but there are other benefits such as,
- Sam's Servo Sub weighs 26 grams (less than 1.0 oz.) in comparison to 19 oz (1.2 lb) for the EXUP servomotor/cable assembly.
- No moving parts to wear out. The servomotor assembly is a D.C. motor and position sensor packaged together, whereas Sam's Servo Sub is a solid-state electronic circuit.
- Less electrical drain on the system as compared to the servomotor assembly.
- When compared to simply disconnecting the servomotor, Sam's Servo Sub allows the Ignitor Unit more time to do ignition control (its primary function). The Ignitor Unit cannot simultaneously generate the tach diagnostic (Tach Tango) and control engine ignition; it must take a short 'break' from ignition control to do so. Given the choice, I know what I would rather have my Ignitor Unit doing.
- Absence of the servomotor assembly facilitates easier carburetor access and removal.
- Less 'wear & tear' on your tachometer.
- Less distraction to the driver with the elimination of the 'Tach Tango'.
Q. I have heard that you can disconnect and remove the EXUP servomotor assembly and simply connect either a jumper-wire or a 7.5K ohm resistor between the black/red and the white/red wires from the R1 wire harness, which previously connected to the servomotor assembly. By doing so, this will then eliminate the tach diagnostic. Is this correct?
A. Yes it is, to a degree. Fitment of the 7.5K ohm resistor or jumper-wire as described above will eliminate the tach diagnostic for all conditions except for when,
- The ignition key is in the 'ON' position and the engine is not running for a period of time greater than 12 seconds.
- With engine idling, 'coasting' with the clutch lever pulled in.
We believe Sam's Servo Sub is superior to the 7.5K ohm resistor or jumper-wire because,
- Sam's Servo Sub eliminates the tach diagnostic under all conditions and does a superior job of simulating the servomotor assembly as compared to the 7.5K ohm resistor or jumper-wire. See Chart for technical detail.
- The voltage measured at the white/red wire when using the 7.5K ohm resistor or jumper-wire fluctuates by a proportionately large amount (see Chart) that indicates the Ignitor Unit is varying its servomotor output by a relatively large amount. This indicates that the Ignitor Unit is being kept busy with a larger portion of 'servo duties' as compared to 'ignition tasks' than does a system with either an EXUP servomotor assembly or Sam's Servo Sub. Bottom line... with the 7.5 K ohm resistor or jumper-wire, your Ignitor Unit is spending more than it's intended/designed time performing servo control rather than ignition duties... not good.
- Dyno data shows Sam's Servo Sub has an advantage of as much as 1.0 peak horsepower over the 7.5K ohm resistor, jumper-wire or even the original EXUP servomotor assembly!
Q. I have heard that the EXUP positional signal (voltage on the white/red wire) is used by the Ignitor Unit (black box) to adjust/vary the ignition spark timing. If this is 'correct' and if the data in your Charts were correct, it would seem that Sam's Servo Sub would provide a more 'correct' signal to the Ignitor Unit as compared to the 7.5K ohm resistor or jumper-wire, thus allowing the Ignitor Unit to provide the correct Ignition timing. Would you agree?
A. I would like to tell you, "Yes, exactly. That is why Sam's Servo Sub is a more correct choice than either the 7.5K ohm resistor or jumper-wire." But if I did I would be guilty of not being honest. Dyno data supports the position that the EXUP positional signal is used by the Ignitor Unit solely for the purpose of EXUP valve positional control, nothing more.
Q. If I replace my stock exhaust canister with an aftermarket slip-on muffler, do I need to replace my servomotor assembly with Sam's Servo Sub?
A. No. Doing so will decrease engine performance and has the potential to cause engine damage.
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