When performing an ignition timing check at idle speed of 800 RPM, by how many RPM should the technician increase the engine speed?

Increasing the engine speed by 100 RPM when performing an ignition timing check is important for ensuring that the timing is accurate and can be adjusted as necessary. At idle speed, the engine's performance may not reflect its behavior under load or higher speeds, so slightly raising the RPM allows for a more accurate diagnosis of the ignition timing's effectiveness as the engine transitions from idle to a higher operating condition.

This increase helps technicians observe changes in timing, ensuring that the ignition system is functioning properly across a range of speeds. A 100 RPM increase strikes a good balance—it's enough to see a meaningful change without pushing the engine into an entirely different operational range, which could potentially complicate the timing analysis. This method is highly accepted in smog repair and maintenance practices to assure compliance with emissions standards and overall vehicle performance.