Synchronisation d'une Suzuki VX800 avec le dépressiomètre TwinMax

Suzuki VX800


"It all starts with the certainty that my engine no longer responds correctly to acceleration, that the RPM no longer matches that of before / speed and higher fuel consumption. I drive around town but still, 8L/100 is too much!"

"So if you keep putting it off, you've got to go for it, because the investment is worth it: between €100/150 for synchro at the mechanic's for three hours (for the first time, or one hour the next time) and €99 all-inclusive: the TwinMax comes with two M5 bits, O-rings and a 9V square battery. Plus, the ability to learn (always important) and redo at will, as much for myself as for others if need be."

"Even if this device is given for a twin-cylinder, it's possible to use it for a 4-cylinders! no contest!"

"I wanted to start from scratch, so I first checked the two carburetors: tank level, cleaning of the interior and jets, condition of the perforated membranes that I had repaired two years ago, following grandpa's advice (sewing + glue) and which are still good... Thanks !!!!!"

"I also wanted to adjust the synchro cable, carburetors mounted. Not to be done, it's a big pain to get the keys in. I should have done it when disassembling the two carburetors, but I did them one by one."

"So a little time, and a fairly empty tank, got me started! So I went back to all the topics, known, German included, the RMT, the workshop manual (both of which only give an idea of the settings) and the technical data sheet for the device. Everything is useful the first time."

Step 1

Locate the two holes (Phillips-head screw + gasket) for the two M5 end caps, one on the left-hand side for the rear, the other on the right-hand side for the front. As I don't have the hands of a midwife, I sawed off one of the end caps and screwed it in with a flathead screwdriver.

For the front, don't connect to the socket fixed to the intake pipe, which is essential for the rear carburettor vacuum, or do as the Germans do and use a Tee on this pipe, which seems more sensible to me, but well, I hadn't planned on it!

Disassemble the air filter balancing box (leave hanging).

Step 2

Dismantle the tank, and pass the feed hose over the frame so that you can lift it to pass the Phillips screwdriver to adjust the idle speed of the front cylinder, and the 8 mm wrench to tighten the lock nut.

Step 3

I taped the device to the top of the tank to keep my hands free for easy, permanent reading. I connected the two hoses to the carburetors. I chose the left outlet for the rear carburetor and the right outlet for the front carburetor.

This choice influences the settings: increase or decrease of the front or rear carburetors, as the two carburetors are synchronized at 0. The needle moves left or right according to this choice. It is according to this choice that you will have to feel your way around to find out which action is the right one.

Step 4

The TwinMax datasheet is self-explanatory. First of all, set the zero point of the device: Sensitivity (left-hand button) to max and adjust with zero (right-hand button). This important setting is very sensitive.

Step 5

Warm up the engine. To start with the idle adjustment, I did it without the synchro cable properly tensioned, which incidentally calls into question its true function (the only one I can see is to adjust the front cylinder idle if you increase the idle on the adjustable rear cylinder screw).

This is where it comes in handy to lift the tank to access the front carburetor adjustment screw. Eventually, I plan to change it for either a "knurled" screw like on the rear, or a BTR.

Adjust both carburetors to reach zero with increased or even maximum sensitivity. The device is sensitive enough to pick up the vacuum variation between the two cylinders, so the needle swings left and right very quickly. You therefore need to find and consider your own fine-tuning.

Step 6

Once the idle speed was set, I adjusted the tension of the synchro cable (which was a real pain). Up the revs to 2000, 3000rpm and adjust the synchro using the two accelerator cables.

Here again, it's a pain to get the 8 and 10 wrenches for the locknuts. I recommend the use of ring wrenches, which will have to be sawn to fit through the accelerator cable!

For maturing (cheese), choose your own tolerance, as the maximum is 1/8 turn of tension. On the cables, deflect the needle to one side or the other; it's very precise and sensitive.


You have to have done it once and fumble around a bit to realize that it's not rocket science. I haven't been able to check the fuel consumption yet, but I've reduced the number of engine revolutions/speed. I can feel the engine breathing better and, above all, reacting better to the throttle, which is really pleasant. 

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