The idle fuel and idle air are controlled by two separate adjustments. The injection pump arm and throttle arm should both be against their idle stops; this means the linkage plays no role in synchronizing idle fuel and idle air when the engine is idling in neutral. Therefore, it is necessary to synchronize the idle fuel and idle air manually. It is a repetitive, trial and error procedure.

The procedure basically involves adjusting the idle fuel setting, then adjusting the idle air valve for best idle, then checking idle speed to see if it’s correct. If it’s not correct, you try another idle fuel setting, readjust the idle air for best idle, and recheck idle speed. This procedure is repeated until best idle and correct idle speed are achieved.

Note: Before adjusting the idle, all other aspects of engine operation should be as perfect as possible: points and timing properly set, good plugs, valves properly adjusted, no leakage at the Cold Start Valve or thermostatic warm up system, linkage properly adjusted and the throttle valve must be fully closed.

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Britton McIntyre

68 280 SE coupe 'Hairball'
70 280 SL
71 280 SEL - RIP May 2010