Friday, April 2, 2010

Dynamic timing

The points made regarding the crankshaft pulley timing marks (or lack of the same) are equally appropriate to dynamic timing. If you are unable to establish where the timing mark should be then consult a good workshop manual or preferably have the job attended to professionally. If you take the latter course then the person who carries out the test will make a timing mark on the crankshaft pulley, which you can later make permanent with a centre punch for future reference!Assuming that you can establish the correct timing mark, proceed as follows. Disconnect the vacuum advance pipe from the carburettor. Highlight the timing mark using typists' correction fluid. Disconnect plug lead number one and connect the two leads from the stroboscope to the lead and plug respectively. Start the engine and shine the strobe onto the spinning crankshaft pulley. The stroboscopic light will flash every time number one spark plug fires, and appear to arrest the motion of the crankshaft pulley so that you can easily compare its position relative to the crankcase join t.11 the notch or other timing mark appears to the left of the crankcase joint then switch off the engine and retard the ignition by moving the distributor slightly in the direction of the rotor arms travel, or vice versa.
The problem with attempting to adjust the air/fuel mixture at home is that there is no accurate method of objectively testing the results of your efforts unless you possess one of the small exhaust gas analysers which are today available for the DIY motorist. Now that exhaust gas is measured as part of the UK annual MOT test, it may be as well to ask that the mixture is set by the tester before your car is tested. Otherwise, it should not take too long nor cost too much to have this small job carried out professionally every six months. Even accurately setting the tickover (750 rpm for most models and 850 rpm for cars with semi-automatic gearboxes) requiresthe use of specialist equipment. However, if you wish to do the work at home, these are the basic principles. Begin by warming the engine then adjust the throttle adjusting screw (which bears against the throttle lever) until the revolutions rise to just under 1000 rpm (fast idle). Then turn the mixture control screw slowly clockwise until the point at which the engine begins to run erratically (the mixture is weak) and turn back by 60 degrees (one third of a complete turn). Re-set the tickover. As stated, it is best to have this work carried out by a professional with the aid of an exhaust gas analyser, and you would normally only carry out this adjustment following an engine or carburettor rebuild, in order to get the engine running well enough to make it to your local garage!
In addition to the home exhaust gas analyser machines now available, a number of devices are advertised to make setting mixture easier. Chief amongst these is the Colourtune system, which uses a special spark plug which allows you to see the combustion colour and adjust the mixture to obtain the correct colour and hence the appropriate mixture.
Still on the subject of fuel, check the fuel tank and lines for leakage.

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