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Fuel Injection System


Unlike carburettors, which often need re-adjustment, fuel injection systems require minimal maintenance as long as all the electronic components are in working order and the system is kept clean.

To prevent soiling, a fuel system cleaner should be used in the fuel tank when the motorcycle is not in use to prevent resinous deposits. Also, the air filter service intervals should always be adhered to.

vacuum connections
Vacuum connections/rubber plugs

Just like multiple carburettor setups, the fuel injection system in multi-cylinder engines has multiple throttle valves, the synchronisation of which is crucial to smooth engine running. The throttle valves are opened and closed by the throttle twistgrip, thereby regulating the quantity of air and fuel supplied to the engine at a given moment. Due to mechanical stress, the basic setting of the throttle valves changes slightly over time and, as a result, the engine becomes noticeably out of sync when idling. You can hear it from the sound of the exhaust system and also see it from a fluctuating engine idle speed on the tachometer – put simply, the engine no longer runs smoothly. It's time to resynchronise the fuel injection system.

fuel injection system
Other fuel injection system installed without air filter

To adjust the fuel injection system, you need a synchroniser, such as the ones from Rothewald for 2- or 4-cylinder engines. Also the adjustment tools are very useful for some models. Before you start adjustment, warm up the engine so that the cold-start device does not falsify the readings. Then place the motorcycle securely on the stand – ideally in the open air but, if inside in a garage, always so that the exhaust fumes can escape directly to the outside without you breathing them in while you work.

synchroniser vacuum tubes
Connecting synchroniser vacuum tubes

Connect the tubes of the vacuum gauges to the connection points on the fuel injection system after first removing the rubber plugs or tubes from the connections.

We recommend:


Spare gauge in case of
loss or defect!
Measuring range 0/ -1 bar


To the product
fuel tank
Lift out tank and secure, e.g. with a piece of wood

If the tank covers the fuel injection system, it must be raised and supported on a plank of wood, for example. Often the tank cannot be removed entirely because it contains the fuel pump. The pump is actuated by the control electronics and is required for the engine to run.

fuel tank
Tank must be secured to prevent it slipping

When "propping up" the tank, make sure that it cannot slip and cause injury or annoying damage to your motorcycle!

air filter housing
Air filter housing must be removed

In addition, on our demonstration bike, the airbox must be removed to get at the fuel injection system.

bypass screws
Bypass screws: set same values on all gauges

Now you can start the engine and begin adjusting the throttle valves by screwing the bypass screws in or out until all gauges show the same readings.

adjust the pointer damping
Adjust the pointer damping

By doing this, you adjust the small air gap opened up by the throttle valves when idling so that air is sucked into the combustion chambers on all cylinders at exactly the same vacuum and at the same rpm, and thus the engine works uniformly on all cylinders. To enable you to correctly read the gauges, they must first be calibrated to each other according to their instructions for use, and the damping must be adjusted so that the pointers flutter only slightly.

When adjusting the throttle valves, generally the aim is not to set a specific vacuum – most motorcycle manufacturers do not specify one – but to achieve the same value on all the throttle valves. Then the system will work "in sync" for all cylinders. If one gauge shows a completely different reading from the others, this may indicate that the basic setting of that throttle valve is completely wrong, or it may mean there is a fault or damage such as loss of compression on one cylinder or a leaking intake manifold. If you cannot find and rectify the fault yourself, then you must go to a motorcycle workshop. The throttle valves are adjusted using the so-called bypass screws (see Fig. 8). Never touch other sealed or colour-coded adjusting screws! All bypass screws should be open at least half a revolution.

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the experts

The Louis Technical Centre

Problems getting spare parts? Or maybe you've got a technical question about your motorcycle or an accessory The Louis Technical Centre can help! Remember to quote all the necessary details of your vehicle – better still, send us a copy of your registration document.

We will get back to you as quickly as possible!

So: send us your technical problem!

Please note!

These tips for DIY mechanics contain general recommendations that may not apply to all vehicles or all individual components. As local conditions may vary considerably, we are unable to guarantee the correctness of information in these tips for DIY mechanics.

Thank you for your understanding.

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