We frequently receive questions about how the auto-choke and its operating needle work. It’s a convenience that gets a bad rap from those desiring the control of a manual choke. To the auto choke’s credit, usually problems starting and running on a GY6 engine are related to dirty carburetor jets, but the auto choke system can be to blame sometimes as well.
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A case of identity confusion
As it turns out, the auto-choke isn’t a choke at all. That is, it doesn’t choke airflow through the carburetor like you would find on a lawnmower or generator type of engine. Instead, it sends extra fuel through the carburetor. This is called an enrichment circuit.
The Choke Regulator Resistor
The function of the choke resistor is to make sure that your choke doesn’t get hit with a deadly dose of over-voltage at high engine RPMs. If this resister goes bad, the choke will likely become damaged shortly thereafter.
How it all works
This circuit is controlled by the charging system. When your engine is off, the choke (enrichment circuit) is actually “on” in it’s default resting state. When the engine is turned on and voltage is applied to the choke, the needle extends and eventually plugs the enrichment ports within the carburetor. This happens within a couple of minutes as the engine warms up.
Testing your Auto Choke
What we usually see with a bad auto-choke is that the engine will start up and run great cold, but as the engine warms up there will be problems driving, starting, and/or idling.
- Remove choke assembly from the choke holder on the side of the carburetor. The needle should be clearly visible.
- Measure the overall length of the choke from end-to-end, including the very tip of the needle.
- Now connect the choke’s electrical leads to a 12v power source. Black is negative.
- Wait 5-10 minutes and re-measure. The needle should have extended.
- The overall length should be approximately 3mm more than before.