What is vacuum retard (negative vacuum)?
Some classic cars have a mechanical ignition distributor with vacuum retard, also called negative vacuum. In these systems, the ignition timing is retarded at idle. The static advance is only applied when the throttle is pressed, meaning the engine is under load.
In short: at idle, the engine fires close to top dead center (TDC). When the engine is under load, the static advance is applied.
How to set up a 123ignition with a vacuum retard curve?
1. Set the engine to top dead center (TDC) on cylinder 1 during the compression stroke.
2. Install the 123ignition according to the manual, but do not yet place the distributor cap.
3. Turn on the ignition.
4. Rotate the distributor housing against the rotor’s direction of rotation:
a. If the rotor turns clockwise (CW) when the engine runs, turn the housing counterclockwise (CCW).
b. If the rotor turns counterclockwise (CCW), turn the housing clockwise (CW).
5. Slowly and carefully rotate the housing until the green LED lights up, then stop precisely at that point. This point corresponds to 0 degrees for the 123ignition.
6. You have now set the 123ignition’s 0-degree point to top dead center. The ignition will now fire at TDC during startup.
7. Secure the distributor, turn off the ignition, and connect the black wire to the coil.
Why do some ignition distributors have vacuum retard?
Due to stricter environmental regulations, vehicles needed to produce fewer harmful emissions at idle. When an engine idles with advance, it can generate higher emissions of pollutants.
To counteract this, vacuum retard distributors were developed. These retard the ignition timing at idle, making the exhaust gases cleaner. However, ignition advance is still needed under (partial) load, so the retard function is only active when the engine is idling.
How does vacuum retard vacuum work in the 123ignition?
The 123ignition with a single vacuum port does not have a second connection for a vacuum retard hose. Instead, a special method is used:
• The 123ignition is set at top dead center (0 degrees).
• At idle, when vacuum is high, the programmed curve ensures that no advance is applied, meaning the engine fires near TDC.
• At partial or full load, the vacuum decreases, and the 123ignition adds a certain number of degrees of advance — the same amount as the original static setting.
• Centrifugal advance is then added on top of this static advance.
FAQs From Same Category
It is always possible to use your original HT-leads for the original look. Even when your engine has solid copper core cables it would work with a 123ignition. For the best performance we advise "carbon tension leads". These cables have a little resistance and very good isolation. Of course you can buy these leads at 123igntionshop.com. See here which sets we sell.
In some cases a very unstable boardnet voltage can cause misfires. The 123ignition is protected against high voltage peaks and goes in protection mode for a split second when a spike is detected. Most of the time this error occurs when the car battery is charged full again and the voltage regulator starts to work. This problem can be caused by a broken alternator / dynamo or bad voltage regulator. Unfortunately this is impossible to measure with just a standard voltage meter because we talk about high voltage spikes of micro seconds. You could easily test this to drive a while without working alternator / dynamo. Use a fully charged car battery and make sure no other important systems are driven by the dynamo belt, like the coolant pump!!!
The car battery has to put enough energy into the coil for a powerful spark. In the higher rpm range the time to do this is very short, so all conditions have to be perfect for good performance. Make sure you are using the right coil for your engine, see: "What kind of coil do you recommend?" Resistance somewhere in the primary circuit can cause a lot of ignition problems as well, think about the following: - Coil and ignition wiring: Use good connectors and cables of good quality - Ignition key: Make sure the dashboard ignition key is in good condition ( test to power the ignition/coil direct from the battery ) - Ground connection of the distributor: Make sure the distributor makes a good electrical connection with the engine.
Always use the spark plugs for your engine specified by the manufacturer of the car!