Prior to the early 80's, YAMAHA, SUZUKI, and KAWASAKI were the reigning two-stroke manufacturers in the world market. In many cases, the ignition timing on older 2-stroke models was expressed as "∆mm before top dead center" rather than "◎ degrees before top dead center". This YAMAHA FS1 is 2.2mm degrees before its top dead center.
In many cases, the ignition timing of 4-stroke engines is generally expressed in terms of "◎ degrees (angle) before top dead center". On the other hand, 2-stroke engines are often expressed in terms of "∆mm (mm) before upper dead center". As with the 4-stroke engines, some Dells are expressed in terms of "◎ degree before top dead center," but most of the models introduced before the early 80's, before the heyday of the 2-stroke engine, are generally expressed in terms of "∆mm before top dead center.
Here's how to adjust the ignition timing on the YAMAHA Sport 50FS1 (with the same type of engine as the YAMAHA YB1 series engines released in the late 1990s and early 2000s).
A OEM special tool for checking top dead center is useful.
A tool for checking the top dead center of the YAMAHA original special tool (This product consists of an adapter tool to be set in the spark plug hole of 90890-01252 and the dial gauge itself, with an extension probe to be purchased separately). It can be used if the angle of screwing in the spark plug is perpendicular to the reciprocating motion of the piston, but it cannot be used properly if the spark plug is screwed in at an angle.
Make sure that the piston is near the top dead center and then tighten the gauge and the gauge preset on the adapter to the spark plug hole. Hand-tightening is sufficient for this process. After tightening the adapter, place the tip of the stylus to the top of the piston and while the gauge is in operation, hand-tighten the fixing bolt on the adapter side to align the "0" point.
If the cylinder head spark plug hole is a slant-tightened model, it's a good idea to remove the cylinder head once and use a dial gauge to find the exact top dead center. The basics of ignition timing start with "finding the correct top dead center".
Upper dead center and inner flywheel pointer are aligned
If the model has a pointer on the inside of the flywheel, check the top dead center and make sure this pointer matches the tick marks on the flywheel side. If the flywheel has a tick on the outside of the flywheel and the crankcase has tick marks on the side of the crankcase, make sure that the tick marks match each other.
For some reason, this FS1 does not have any tick marks on the flywheel side or pointers on the crankcase side. In such a case, you can tentatively use an oil-based pen to make a mark on the flywheel side.
In the case of the Yamaha FS1, the ignition timing is instructed to be 2.2mm before the top dead center. After confirming the upper dead center, slowly reverse the crank and stop the engine when it passes 2.2mm before the top dead center. Turn forward again and stop the crank at a position 2.2mm before top dead center.
The flywheel side tick marks and the crankcase side tick marks or pointer positions should be confirmed. The reason for this is because without the matching mark, it is impossible to judge whether the ignition timing is early or late in the adjustment inspection. Without the matching mark, it is impossible to judge whether the ignition timing is early or late at the adjustment inspection.
With a point-controlled ignition system, the point contacts open the moment the point heel rides up on the point camshaft, and at that moment, sparks fly to the spark plug electrodes. CDI ignition vehicles with non-contact control are controlled by timing control when the electrodes switch inside the flywheel.
If you have a timing strobe, the flash will light up the moment the sparks fly, allowing you to confirm the current ignition timing. Then we can start the adjustment process.
Let's check the ignition timing while idling.
Set the clamp on the timing strobe to the plug cord (don't mistake the clamp part for the electric current "→" mark) and start the engine. Pushing the switch on the strobe makes the flash light fly intermittently. The moment of this flash is the moment when the point opens = ignition timing. If there is a discrepancy between the mark and the point, loosen the screw slightly and shift the tightening position of the point with a flat-blade screwdriver to adjust the mark to match.
- Point 1 - Let's start by checking the top dead center for 2-stroke engine models.
- Point 2 - According to the data in the ◎mm before the top dead center, a special tool dial gauge is used to find out the position of the piston in accordance with the values.
- Point 3 - A timing strobe is essential to confirm the correct ignition timing.
- Point 4 - Timing adjustment is often done by subtle adjustment of the point tightening position, that is, the outer rotor type, which is done by subtle adjustment of the point gap width.
In the case of the 4-stroke engine, there are data at idle of 6 to 12 degrees before top dead center. Then, when the engine is over 3000 rpm, the ignition angle is advanced to the maximum angle of advance.
In the analog age, and also in the age of point control, the ignition advance angle was adjusted by centrifugal force. In the case of transistor ignition and CDI ignition, which had advanced technology, the ignition advance was adjusted by electronic signal control. Although few in number, there were examples of models that appeared in such a technologically transitional period that had transistor ignition but were equipped with an analog centrifugal governor (the Honda CB750F released at the end of the 1970s was one such example).
In the case of a 2-stroke engine, the angle control is generally not used, but rather data such as "∆mm before top dead center", which means "how many millimeters before top dead center" the piston position is in relation to the top dead center for ignition. This is numerical data at idle, and in the case of a road-spec production two-stroke road motorcycle, there is almost no ignition advance angle, and the so-called "fixed advance angle" is used. However, when a 4-stroke engine is called "fixed advance angle," it most likely refers to the ignition timing after the advance angle is reached, not the ignition timing at idle.
If you open the throttle with the ignition timing at idle after the engine is started, you can understand this, but in the case of a 4-stroke engine, if you don't increase the ignition advance angle, the engine rotation will not be high. On the other hand, by fixing the ignition advance angle in line with the high rpm, the engine can be turned smoothly and comfortably. However, if the ignition timing is fixed at high RPM, the engine may not be able to start up as smoothly as it should.
In other words, the ignition timing is too early at low rpm, which makes it difficult to start the engine consistently.
If you look at the service manual for a production motorcycle with a 4-stroke engine and the ignition timing section details "At idle, B.T.D.C 12 degrees/3500 rpm, maximum advance angle of 35 degrees", you can assume that if you adjust at 12 degrees at idle, the maximum advance angle will go to 35 degrees with the centrifugal governor.
However, when I checked the engine with a timing strobe, I found that although the engine was right on the F mark (fire mark) at idle, it was not within the tick range of the maximum angle of advance even when the rpm was increased. The cause of the bad blowing is probably a defective ignition advance angle.
Supposing that the centrifugal governor was malfunctioning, I removed it and inspected it, but the governor was rusty and would not open to the maximum angle of advance? In such cases, it would be a good idea to spread out the rag and be careful not to lose any parts, and then take the governor apart to remove the rust from the actuator and slide it together. After such maintenance, the engine revs smoothly and smoothly! It's not uncommon to hear stories like this, and I've had that experience many times in the past.
In the case of a 2-stroke engine, the upper dead center of the piston is located, and the upper dead center of the ignition timing data is found by using a special tool. Some models do not have any tick marks or pointers on the flywheel side or the engine side, so in that case, find the upper dead center first. Then, move the piston position according to the ignition timing data listed in the manual, and if it's a point system, do it by tightening the point fixing adjustment bolt so that the point opens at that moment.
For CDI models where the pickup coil is on the outside of the flywheel, the engine should be designed so that the pickup coil sensor position and the flywheel side protrusion position are roughly in line with the data.
If there is a carving or pointer to show the upper dead center, or F mark for ignition timing, the strobe must be adjusted to open the point when the flywheel approaches the F mark. However, such adjustment is only for "register", so a matching strobe is necessary to make a precise adjustment.
Even if you think you've adjusted your register to match the F mark at the moment the point opens, you may find that the timing is too early or too late. With a timing strobe in hand, I can easily make subtle adjustments to ensure a perfect match.
