Electronic Throttles

Introduction

This section has been extracted (and expanded) from the various bike-specific wiring diagrams.  Throttle issues account for many problems with electric trials motorcycles, perhaps because the throttle is so vulnerable in a crash.  

For example, if the voltage produced by the throttle is too large when the siliXcon controller boots, the motor will emit error beeps and fail to run.  This is a safety feature that keeps the bike from “taking off” with no throttle input from the rider. 

There are two basic types of electronic throttles:

• Potentiometer (often shortened to just “pot”)

• Hall-effect

A potentiometer is a variable resistor.  A potentiometer-type throttle is presently being used on all the EMs and Mecatecno's Dragonfly.  One end of the pot is connected to a reference voltage (typically 5 VDC) and is called the high side.  The other end connects to signal ground and is called the low side.  The pot's movable wiper (also called the sliding contact) forms a voltage divider producing a variable output between zero (shut) and the reference voltage (wide open).  The voltage is linearly proportional to throttle position.  Some throttles have added features like a redundant pot for safety (both must agree, or an error condition is signaled).  Another optional feature is a microswitch that can indicate the throttle is fully closed or fully open.

The Hall-effect is named after Edwin Hall who discovered it in 1879.  With a Hall-effect type throttle, an electronic circuit senses the movement of a magnet.  There is no physical contact between the magnet and the sensor, which improves mechanical reliability.  This type of throttle is typical in low-cost applications like e-bicycles.  I wondered why they're not more popular, and decided to conduct a linearity test.  You will find a table for the Sur Ron throttle near the end of this section.  Spoiler alert, it's not at all linear.

With both types of throttles, only the middle of the voltage range (typically around 1 – 4 volts) is allocated to actually controlling the motor.  The lower extreme (0 – 1 volts) and the upper extreme (4 – 5 volts) may be used to provide safety features such as broken-wire detection.

Magura 317 Throttle

The Magura type 317 throttle is made in Germany.  It uses a nominally 5k ohm potentiometer to form a resistive voltage divider.

Its wire colors are assigned as follows: 

• Brown = common (ground)

• Blue = reference voltage (typically +5 VDC)

• Black = wiper (output)

The wiper voltage starts at 0 volts and progresses linearly to the reference voltage.

Not only is this throttle used on various EMs (including the 5.7), it's also found on the Mecatacno Dragonfly.

The throttle is available as EM part number TL01N-60401-00-00.  As of April 2026, it retails for $182.88 USD.  Generic Magura electric throttles cost about $90 via eBay, but don't have the EM-specific JST JWPF connector.  

If you go the generic route for replacement, most riders will probably be satisfied simply cutting the connector off their original throttle leaving a short length of wire to splice into a new throttle.  Frankly, the OE wires could stand to be a bit longer anyway — especially if you use handlebar risers.

But if you want to fabricate a complete spare throttle, or are just fastidious, the photo below should be helpful.  Note the orientation of both the connector itself (which shows the sequence of the various wire colors) and the orientation of the pin relative to the connector.

When using the Engineer crimping pliers on JWPF pins, the 1.9 mm size seems to work well for the bare part of the wire and the 2.0 for the insulated part.  I recommend practicing on scraps beforehand.  There's more information on JST connectors and the Engineer crimper here: https://www.electricmotiontech.com/home/em-epure-race/wiring-diagram

Magura Deadband (Free-Play) Adjustment

I'm defining “deadband” as the amount the throttle must be mechanically rotated before it causes any movement of the motor.  Think of it as adjusting the throttle cable free-play on an internal combustion engine.  (Additionally, the controller itself will have a setting for the voltage at which the throttle begins to take effect.  Kelly Controls calls this parameter the “effective starting voltage.”) 

A preference I learned from riding ICE motorcycles is to have the absolute minimum of throttle free-play.  But trying to apply this to electronic throttles is not without complications. 

Newer trials bikes allow electronic adjustment of throttle free-play via phone apps like EM Connect and Youmapp.  But older bikes lack this capability, and a few degrees of rotation can make a big difference.  I expect Magura/EM sets the throttle up with “excessive” free-play as a safety precaution.

Electric Motion made a video on the adjustment procedure.  A screen capture of the most relevant part is shown below.  Basically, you must loosen a locking screw that bears against the potentiometer so that it is free to rotate.  EM advocates carefully prying against the wires to rotate the potentiometer.  But this is bad advice.

Years ago, I was successful in this endeavor and achieved nearly zero free-play.  But due to component aging and likely some physical changes in the mechanism, the motor would occasionally emit error beeps (as if the throttle was partly open when engaging the first map).  The motor still ran, but I was concern it might leave me stranded. 

The next photo shows the repair I made.  The brown wire broke off at the body of the potentiometer and left nothing for soldering.  Luckily, I was able to use a Dremel type tool with a very small burr to remove plastic from around the broken pin.  Although not strictly necessary, I used a solder with a 4% silver content when reattaching the wire.  I feel this makes a stronger bond when there is little mechanical strength in the joint.  I also applied an old-fashioned glue called Duco Cement around the solder joint for added mechanical strength. 

As for the divot, after trimming the plastic with a sharp knife, I filled that with Duco Cement too.  A bit of filing produced a new smooth surface to again set the free-play.  

Unless you are proficient at building ships in bottles, this work really needs to be done with the potentiometer removed from the throttle.  But that introduces the complication of reassembling everything properly again.  

The other photo shows the homemade “pick-off” connector I use to measure voltages in the throttle circuit.  It has a male connector at one end and a female at the other.  It's intended to be inserted temporarily between the controller and the throttle.  It can also be used to easily make resistance measurements when the throttle is not in-circuit.  Note there is a small segment of insulation removed from each wire for making connections to test equipment.  This should be done in different locations along the length of the wires to prevent accidental short circuits.

The key point in achieving a small throttle free-play is that the closed-throttle voltage (measured between brown and black wires) must be slightly more than zero volts (let's say 0.1 V). 

Magura 317 Repair Tips

Repairing a Magura e-throttle is possible, but not necessarily easy.  I'll share what I have learned.  The work needs to be done with the throttle removed from the bike, but a section of 7/8" tubing may be helpful to hold the throttle during some operations. 

There are a total of six Phillips screws: 

• There's no need to completely remove the two largest screws that clamp the throttle to the handlebars.

• The smallest screw fastens the cable clamp.   

• The next-smallest screw bears against the potentiometer to lock it in the proper orientation.  This is the one that causes all that problems.  When this screw comes to bear tightly against the plastic, it creates the divot. 

• Two medium screws hold the housing halves together.  The handgrip must be removed to access them.  Although it may be possible to non-destructively remove the OE handgrip, I always cut it off with a razor knife as I prefer different grips anyway.

I have a fear of disassembling anything that contains a spring, as it's sometimes next to impossible to get it back together without the special tools and fixtures used by the OEM.  Fortunately, the Magura's return spring was surprisingly easy to reinstall.  There is a hole in the throttle tube and the housing for each end of the spring. 

Note the area outlined in yellow in the photo below.  A protrusion on the plastic part of the potentiometer fits into this area to limit adjustment range.  Although the body of the potentiometer has a limited range of adjustment, the shaft position is more unconstrained — it must be roughly correct prior to aligning the gears.  A simple way to do this is by measuring the resistance between the brown and black wires.  It should be in the neighborhood of 75 to 100 ohms with the throttle shut.  The higher the resistance, the greater the resulting voltage will be when installed and operating on the bike.  

I recommend temporarily reassembling everything and making electrical measurements prior to fully tightening the divot-creating screw.

The next section provides some measured electrical values for reference. 

Measured Electrical Values

As part of reassembling the throttle, I set the potentiometer correctly prior to installing it on the bike.  The electrical values below may help with troubleshooting and to set your throttle properly:

• My nominally 5k ohm pot actually measured 5.42k ohms.  Measured between brown and blue wires.

• The siliXcon controllers provide a nominally 5 volt reference for the throttle pot.  Measured between brown and blue wires.  The SC controller in my EM Race actually measured 4.81 V.

• My EM Race needs a throttle output of about 1.1 volts for the rear wheel to begin to turn (unloaded).  It will continue to turn down to about 1.0 volts (again unloaded).  Measured between brown and black wires.

• Note that the siliXcon controller's analog input port resistance is abo­ut 69k ohms.  This loads the potentiometer's output voltage slightly.  With an unloaded 1.0 volt output, the loaded voltage drops by about 20 mV.  This is not really significant, but I mention it for completeness.

• If you must turn the throttle at all prior to getting to approximately 0.1 volts, then excess free-play will result.  However, in my initial desire to achieve minimal free-play, I took this too far.  With the throttle released, the voltage into the controller was 0.65 – 0.73V (depending on how the throttle snapped shut).  I expect anything more than about 0.4 volts may be too much for long-term reliability (due to component aging and mechanical changes).

My Safety Modifications

Below is a photo of the modifications I make to all trials throttles.  The most import one is to use some type of bar-end plug.  This helps ensure the throttle won't stick open after planting it in the dirt.  I made the one shown here, but they are readily available in the aftermarket.  This requires cutting the handgrip.   There's also a homemade white plastic “doughnut” between the grip and the throttle assembly.  This helps reduce friction should the soft handgrip come into contact with the throttle assembly.  I like to secure the grip to the throttle tube with aviation safety wire (sometimes called lock wire).  Finally, I always use a dry lubricant (graphite powder) between the inside of the throttle tube and the handlebar. 

Domino Throttle

EM replaced the Magura throttle with an Italian-made Domino unit starting with the middle of the 2022 model year.  It is part number TC01Q-60401-00-00-ASM.  As of April 2026, it retails for $207 USD.

A friend who owns both a 2021 and 2022 Race says the Magura throttle exhibits about 72 degrees of rotation whereas the Domino is only about 60 degrees.  However, this may or may not translate into quicker throttle action.  My experience has been that the controller produces full torque before ever getting to full twistgrip rotation.

The wiring diagram below is for the standard throttle Domino sells for electric vehicles.  It has a 5-position Amp Superseal connector.   The photo below shows the 2022 EM throttle wiring using JST connectors.  The microswitch is not used in EM's implementation.