The position of the trimmer regulator valve is controlled by modulator pressure. During closed throttle or light operation, modulator pressure is ___________.

• A. High
• B. Non-existent
• C. Relatively low
• D. Varied

Answer: (A)

The regulator valve’s position is driven by the pressure from the modulator, so the valve can be moved to keep the engine running smoothly at different throttle positions. When the throttle is closed or the load is light, the system is in idle/low-demand mode, and the regulator circuit is designed to maintain stability by applying a higher modulator pressure. That higher pressure biases the trimmer regulator valve toward a setting that trims fuel appropriately for idle, preventing stalling and minimizing idle fluctuations.

Think of it as a bias: at idle, the modulator pressure needs to be on the higher side to hold the valve in the position that keeps the engine running smoothly with the least fuel without surging. If there were no pressure, or if the pressure were kept low or wildly changing, the valve wouldn’t reliably maintain idle stability.