posted 06-17-2006 09:12 AM ET (US)            

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"Sync and Link" is a procedure performed on engines (especially two-stroke engines) with multiple carburetors. The position of the throttle plates of the carburetors are adjusted so that they open and close in synchronism, and the mechanical linkage between them is adjusted to maintain this setting.

Sync and Link is an important procedure because on a two-stroke engine with multiple carburetors, the fuel induction path is often arranged so that each cylinder receives its fuel and air mixture from a single carburetor. This is in contrast to most four-stroke engines where there is an intake manifold that distributes the fuel and air mixture from a single source to all of the cylinders in common. On the two-stroke engine, it is very undesirable that a cylinder be running with insufficient fuel. This creates a lean combustion condition. Lean combustion leads to higher combustion chamber temperatures, which in turn can lead to detonation (premature ignition). This can cause serious damage to a cylinder and piston. By setting the multiple carburetors to operate in synchronism, all cylinders will receive the same fuel and air mixture as the throttle is moved.

posted 06-17-2006 09:26 AM ET (US)            

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To perform a Synch and Link procedure, the air intake silencer is removed so that the technician can observe the position of the throttle plates of the individual carburetors. The linkage between the carburetor throttle plates is loosened, and then the throttle plate positions are then set according to the manufacturer's recommendation. The linkage is then tightened. There are also mechanical limits or stops which are adjusted to prevent the remote throttle lever from being able to apply too much movement to the linkage and damage it. The idle position is also usually set at this time. This procedure will be explained in detail in the manufacturer's service manual for your engine.

On some more exotic multiple carburetor installations, specialized venturi gauges may be used to measure the actual air flow into each carburetor. This is probably only normally done with racing engines. On most outboards the Synch and Link is usually done by visual alignment of the throttle plates.