Stick a tube on it a suck you should be able to seal tube with your tongue and need to pull it off. If you cannot get a vacuum in tube the unit is caput. You may also like to check if you can get a vacuum that the plate in the distributor that the vac unit connects to is actually moving. sometimes they sieze up and need freeing off.
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Khryztal
New Member
Hi wammer.
Just finished rebuilding the dizzy. Completely stripped it down. The weigths were seized solid to the main shaft. The vacuum unit on my dizzy has 2 ports. 1 at the front and 1 at the rear of the unit. You can stuck air through the front port but nothing from the back. Sucking on the front port does not move anything.
I did have to free the plunger coming out of the unit though.
Still sucking air and no movement
Just finished rebuilding the dizzy. Completely stripped it down. The weigths were seized solid to the main shaft. The vacuum unit on my dizzy has 2 ports. 1 at the front and 1 at the rear of the unit. You can stuck air through the front port but nothing from the back. Sucking on the front port does not move anything.
I did have to free the plunger coming out of the unit though.
Still sucking air and no movement
david451
New Member
You need to get a timing light on it, yes sucking it will indicate it moves but it is meant to advance retard the timing a given figure without the light it could be miles out, and off course how do you know its getting vac from the manafold properly, however with the engine running you should hear and feel it sooking with the hose off.
Can only summise that the one you can suck air through opens a NRV to release the vacuum on the other side. A vacuum applied to the other one should cause the diaphragm to move the rotating plate to advance the spark. If there are two pipes feeding it make sure you put the correct pipe on the correct connection. They will be connected to different points on the manifold or plenum the one that advances the spark will most likely be connected before the throttle valve the one that opens the NRV after it. I have a Porsche with a simular system. As the throttle is closed the vac is released retarding the spark. Most likely to prevent back fires. As the other poster says a timing light will tell you if the vac is working it would also tell you if you had the pipes on the wrong connections.
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