Zenith 267 Carburetor Idle Circuit Guide
The idle circuit in your Zenith 267 carburetor plays a critical role in keeping your engine running smoothly when you’re not pressing the throttle. Understanding how the idle circuit works and what can go wrong is key to diagnosing rough idling, stalling, or poor fuel economy.
How the Zenith 267 Idle Circuit Works
When your engine is at idle speed, the throttle plate is nearly closed, which means very little air flows through the main venturi. Instead, the engine relies on the idle circuit to supply the fuel it needs.
Here’s how it works:
Fuel is drawn from the float bowl through a small idle jet.
The fuel mixes with air in an emulsion passage to create a fine mist.
This air-fuel mix exits through idle discharge ports located just below the throttle plate.
The idle mixture screw controls how much fuel enters the engine at idle RPM.
When the throttle is opened slightly, fuel also flows through the off-idle transfer slot to prevent hesitation until the main metering system takes over.
Common Zenith 267 Idle Circuit Problems
1. Rough Idle or Stalling:
Caused by clogged idle passages, a plugged idle jet, or an air leak at the carb base gasket or throttle shaft.
2. Idle Mixture Screw Not Responding:
Often means the idle passages are blocked by old fuel varnish or debris.
If the throttle plate is open too far (high idle speed), the carb is pulling fuel from the main circuit instead of the idle circuit.
3. Hard Starting:
Can happen if the idle circuit is restricted or adjusted too lean.
Always make sure the idle mixture screw is adjusted correctly for smooth idle.
Tips for Adjusting the Zenith 267 Idle Mixture
Warm up the engine to normal operating temperature.
Turn the idle mixture screw in gently until it seats—never force it.
Back the screw out 1½ turns as a starting point.
Adjust slowly in or out until you get the highest, smoothest idle speed.
Re-set the idle speed screw if needed so the throttle plate stays mostly closed at idle.
Keep Your Idle Circuit Clean
A clean idle circuit keeps your Zenith 267 carburetor running the way it should. If your carburetor has been sitting for a long time, old fuel can clog the tiny passages. A proper rebuild or using a high-quality Zenith 267 carburetor kit will restore smooth idle performance and help prevent stalling.
Need parts or help rebuilding your Zenith 267?
Check out our complete rebuild kits, idle mixture screws, and detailed technical guides to get your carburetor back to factory condition.
