Adjusting your fuel injection system

From time to time, even maintenance-free fuel injection systems need a little attention and resynchronising to ensure your engine runs smoothly.

[HEADER: Adjusting your fuel injection system.]

Step by step: How to adjust your 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, you should always adhere to the air filter service intervals.

[IMAGE: 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 tell from the sound of the exhaust system, and also from a fluctuating engine idle speed – put simply, the engine no longer runs smoothly. It's time to resynchronise the fuel injection system.

[IMAGE: 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.

[IMAGE: 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.

[IMAGE: fuel tank.]
Lift out tank and secure, e.g. with a piece of wood

Gaining access to the fuel injection system

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

[IMAGE: 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!

[IMAGE: 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.

[IMAGE: bypass screws.]
Bypass screws: set same values on all gauges

Synchronising the throttle valves

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.

[IMAGE: Adjust the pointer damping.]
Adjust the pointer damping

The purpose of this is to 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, which ensures the engine works evenly 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. 7). Never touch other sealed or colour-coded adjusting screws! All bypass screws should be open at least half a revolution.

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[IMAGE: the experts.]

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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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