TwinMax I Carburetor Synchronizer

Suzuki SV 650

Suzuki SV 650
"Many thanks to "Apolon34" for this very complete and well documented tutorial on how to adjust and synchronise the injection of a Suzuki SV650."
The purpose of this report is to make a quick presentation of the injection of our dear SV, and how to adjust them in the best way. The information comes from the technical review.


The injection of our SVs consists of a set of sensors and actuators that achieve a single goal: continuously injecting the right amount of fuel into the cylinders.
To achieve this, we have the following set of sensors at our disposal:
  • Engine flywheel sensor, allows you to know at what engine speed the engine is running
  • Intake air temperature sensor (in the air box)
  • Water temperature sensor
  • Intake vacuum sensor (in the air box)
  • Throttle Position Sensor (TPS)

All this makes it possible to control the injectors, by regulating the injection time, the quantity of fuel injected is precisely controlled.

Then an additional device (the secondary throttle) is added to moderate the opening speed of the accelerator and control the idle speed.

So we add :

  • Secondary shutter actuator (motor)
  • Secondary shutter position sensor
  • Accelerated idle system
Of course, all this can (and must) be adjusted to optimise the operation of the engine.

A top view of the injection (tank up, air box removed):

The sensors/actuators of the air box :



This adjustment is purely mechanical and should not move over time. It is not of primary importance either, as the throttle is usually open enough so that the influence of the sync is negligible.

First of all, we start by disconnecting the STVA coupler (the engine that operates the secondary throttle valve) by unplugging its connector, as shown in the photo below:

The shutter is then operated by turning this knob by hand:

Then for adjustment, the technical journal recommends measuring the length between the throttle valve and the top of the injection body. Personally I don't find this very precise and I preferred to proceed as follows:

I slide a 0.30 wedge between the butterfly and the body and then I close the butterfly with the wheel until I get a "greasy" rub (rubs but passes anyway). Then I remove the wedge and take the same measurement on the other body. (We start with the front cylinder). If the wedge floats or doesn't pass, you have to adjust the synchro, like this:



Once the synchronisation is OK, the STPS sensor setting is changed to the STPS sensor setting. To do this, disconnect the stva connector (see above) and open the throttle fully using the knob (see also above).
Once this is done, the contact is switched on (no need to start) and the voltage between the yellow and black wire of the position sensor is measured. Shutter wide open, there must be more than 4.38v. For my part I have set mine to 4.5v.

Once set, we tighten the sensor and check that it hasn't moved.



Once the secondary throttle valve and its position sensor are OK, the position sensor (TPS) is attacked.
To adjust the setting, first set the motorbike to dealer mode. The secondary throttle is set to the fully closed position to cancel the fast idle phenomenon. When the ignition is turned on, the position of the sensor is adjusted so that the line is in the middle, as shown here:

Sensor view :

I've managed to set it so that it's about in the middle of the range between the bottom line and the top line. After retightening, check that the setting has not moved. You can then reconnect the STVA contactor.



Once everything else is set, only the fast idle is left to finish setting. This will be done in two phases, first the standard idle setting and then the fast idle.

For starters, the standard slow motion. We let the bike warm up on the stand until it reaches 80 degrees. The idle speed is then adjusted to 1300 rpm using the screw on the left side, near the frame. Once this is done, let the bike cool down completely.

View of the idling system :

In fact, the secondary throttle allows the primary throttle to be half-opened (and thus accelerate the idle) when it is wide open. The ECU uses it to manage the accelerated idle speed during the warm-up phase of the engine.

So we're going to start the engine. We use the adjustment screw (not visible on the picture) to adjust the idle speed at the first moments, according to the outside temperature.
Around 50-55 degrees of water temperature, the idle speed should fall back to its normal value (1300 rpm) or a little less.
Once this has been done, the last adjustment to be made is that of the throttle synchronisation.



Once all this is done, we move on to synchronisation. Before doing so, the air box is completely re-installed and the engine is allowed to warm up to 80 degrees. Once it is hot, we switch off the ignition and connect the regulator to the vacuum sockets.

The device, a twinMax :

Before changing the setting, it is switched on and the sensitivity is set to max. The indicator is then set to zero.

View of the vacuum connection of the front cylinder :

View of the rear cylinder vacuum connection :

The plugs on the vacuum sockets are then removed and the twinMax is connected. The easiest way to do this is to slide a small hand through the opening of the frame on the side (as shown in the picture).
The engine is then turned on, left to idle for a minute and then adjusted. We use this screw:

The aim is for the twinMax indicator to be as close to the middle as possible. When adjusting, the idle speed may increase, we will then reset it to 1300 rpm and confirm that the sync is still ok.

Once it's done, remove the twinMax, put the caps back on and it's ready for a little ride!