The ignition timing should also be adjusted depending on the amount of mixture entering the cylinders: the more of it, the less the timing should be, and vice versa. Monitoring and adjustment of these changes occur automatically, but for the entire system to operate in the required modes, the ignition timing of the mixture must be precisely adjusted. How important this is can be judged by the results that occur with incorrect adjustment: with late ignition, due to incomplete combustion of the working mixture, the engine loses power, responsiveness, overheats and consumes more fuel; if the ignition is too early, detonation knocks occur, pistons and valves burn out. The engine also loses power.
The ignition timing is set by matching mark 4 (Fig. 19), located on the crankshaft pulley, and marks 1, 2, 3 on the timing mechanism drive cover. The equipment of the operation with a tool depends on the selected method of setting the ignition timing. The traditional and most accessible method is using a 12-volt test lamp. It is used if there is no special equipment. The second method is using a stroboscope, which allows for the greatest accuracy in adjustment.
With the first method you will need the following tools and equipment: a starting handle, a test lamp with two soldered wires, and a 13 mm wrench. The sequence of operations is as follows:
- remove the cover of the breaker-distributor;
- turn the crankshaft with the starting handle to a position in which the difference plate 1 (see fig. 16) rotor 2 will be directed towards the contact of the wire of the first cylinder in the cover, and mark 4 (see fig. 19) on the crankshaft pulley coincides with mark 2 on the timing mechanism drive cover. This will correspond to the position of the piston of the first cylinder at the end of the compression stroke;
- loosen nut 11 (see fig. 16) fastening of the housing 12 of the distributor;
- connect the test lamp with one end of the wire to terminal 6 and the other to ground and turn on the ignition;
- turn the distributor housing 12 clockwise until the breaker contacts close (the light should go out);
- slowly turn the distributor housing counterclockwise until the control lamp lights up. In this case, rotor 2 should be pressed slightly to select the gap;
- set the distributor housing to the position where the indicator lamp lights up (the breaker contacts will be in the initial opening phase), and, holding the body in this position, tighten the distributor mounting nut.
To specify the ignition timing, it is adjusted with the octane corrector nut or by turning the distributor breaker itself on a warmed-up engine. While driving on a level road in direct gear at a speed of 50 km/h, sharply press the fuel supply control pedal. If this causes minor and short-term detonation, then the advance angle is set correctly. With strong detonation (early ignition) the distributor breaker housing should be turned clockwise if there is no detonation (late ignition) — counterclockwise. After adjusting the ignition timing, its correctness is checked again on a moving vehicle.
In the second method use a stroboscope and a 13 mm wrench. The domestic industry has mastered the production of stroboscopes that operate from the vehicle's on-board network. The stroboscope STB-1 has proven itself to be the best. The device is connected to the engine ignition system so that the flashes of the stroboscopic lamp occur synchronously with the appearance of a spark between the electrodes of the spark plug of the first cylinder. Before starting to check the ignition timing, the breaker-distributor is set to the zero position, and the mark 4 (see fig. 19) on the crankshaft pulley for better visibility, mark with chalk. With the engine running, direct the light from the strobe flash lamp onto the rotating pulley. Since the flashes of the lamp and sparks from the spark plug occur simultaneously, the mark on the pulley appears to be stationary. If the ignition timing is set correctly, then when the engine is running at a low (800-900 rpm) crankshaft speed, mark 4 will always be opposite mark 3 on the timing mechanism cover. If the ignition timing is set incorrectly, the error is corrected by turning the breaker-distributor housing to the required angle.
To increase the ignition advance angle, the distributor breaker housing should be turned counterclockwise, and to decrease it, clockwise. The perfection of the stroboscopic method lies primarily in the fact that the control and adjustment process is carried out on a running engine. This makes it possible to simultaneously check the operability of the centrifugal and vacuum ignition advance regulators. Given the complex organization of the systems and mechanisms of a modern engine, preference should be given to the stroboscopic method.
Since a stroboscope is not always available everywhere, car enthusiasts adapt other devices for these purposes.
As an example, we can describe the proposal of a craftsman from Dushanbe, who adapted the FIL-102 photo flash as a strobe. To implement this task, a storage capacitor C4 (Fig. 20) and a "strobe" mode switch contact S1 were built into the photo flash circuit.
How does this device function? In the "strobe" mode, when contact S1 is open, only capacitor C4, with a capacity of 3 μF, is included in the power supply circuit. In the "flash" mode (when contact S1 is closed) the main storage capacitor C3 with a capacity of 1500 μF also works.
The innovator made a simple design of a capacitive type sensor 100 mm long and installed it on a high-voltage wire. The sensor has a socket 2 for one central electrode, with the help of which the fork of the flash synchronization wire is connected to the sensor. In the "flash" mode, the device connected to the sensor works as a stroboscope. Switch 1 is made of two instrument clamps, separated from each other by a jumper plate.