Curing rough idling

Press, Volume CXI, Issue 32565, 26 March 1971, Page 17

Curing rough idling

Sometimes correcting rough engine idling is just a matter of adjusting the idling-speed screw to -bring engine speed to the manufacturer’s recommendation. But more often, Champion Spark Plug Company engineers report, the causes are elusive, and it is necessary to look at suspected causes of the trouble and eliminate them in order. The engineers give this list of likely causes of ' rough idling: Wrong mixture: adjust the mixture strength needle to lean or enrich the fuel mixture. Usually the ad- . justment is clockwise for a leaner mixture, anti-clock-wise for a richer mixture. Wrong float level: the carburettor usually has to be dismantled to adjust this. Workshop manuals give instructions. Air leaks: usually past de- . fective carburettor or manifold gaskets. Listen for tell-tale hissing sounds which indicate loose bolts or a broken gasket, and also inspect the system carefully. Loose intake manifold: make sure the carburettor

is not loose on its manifold mounting, and that the the manifold is properly tightened to the cylinder-head. Clogged jets: or clogged idle discharge holes. The carburettor should be carefully dismantled and cleaned. Jets can be cleaned with compressed air or air from a tyre-pump. Faulty automatic choke: make sure the choke is coming into operation when the engine is cold, and that it opens fully when the engine warms up. Make sure the manifold heat valve is not sticking. Leaking vacuum hoses: these can be another source of air leaks, which lean the mixture and thus cause rough idling. Check for any loose connections or cracked hoses. Ignition problems: faulty plugs, points or timing, as well as faulty ignition leads, will also cause bad idling. Engine wear: defective engine valves or uneven compression in the cylinders will cause poor idling and running. Take a compression test, or check for weak cylinders by remov-

ing plug wires one at a time and watching for a drop in r.p.m. A healthy cylinder will show a drop in r.p.m. when the pluglead is removed.