Timing in some models is fairly insensitive while in others, it is critical. The Timing Chart (PDF) provided is based solely on our experience. Since every engine is different, you can expect some variation in what works best, so use this only as a guide. If you hear a "fluttering" in the intake or experience a loss of power after advancing the timing, retard it immediately. Retarding the timing too much will reduce power and mileage and cause the exhaust to run excessively hot, possibly damaging it, but it is unlikely to hurt the engine itself. On the other hand, excessive ignition advance can break apex seals and damage rotor housings.
As a general rule, trailing timing doesn't increase the power much, but it is more dangerous than the leading timing to the engine if set incorrectly. When experimenting, advance the leading timing in 2° steps to find the optimum setting, then advance the trailing in 2° steps to find its best position. Finally, retard both 1° or 2° for safety.
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