Thread: Vacuum advance test

Originally Posted by Bulldog

Thanks PLR,

Whats the mechanical advance? I was under the impression that the advance is set with a timing light and then the vacuum adv adjusts it for RPM differences... Is it a system of weights etc?

The elec ignition box is fairly simple and only connects to the dizzy. It is called "Optospark". However if it was clever, it could get the RPMs from the opto wheel in the dizzy and do the advance that way.

Any ideas? Thanks again and apologies for the thread hijack

G`day Pete ,

yep weights , sort of like making a fist and then extending your pointer , that`s sort of how the weights work , 2 of weights 2 of springs . Weights are a sort of half moon shape and pinned at one end they are held closed by springs and as the revs increase the weight spin and open , like your pointer . These control the mechanicl or centrifugal advance .

This is the movement of the rotor that should be there with the cap off .

If your Optospark is a 400 or 500 i`m pretty sure they still require the use of the mech and vac advances . Probably got USA and made under lic in AUS ?

I have a similar Pommy made 1 and it requires both advances it`s made by Newtronics but Piranha here .

If you`ve ever had trouble getting the rotor arm off , it`s common to dislodge the mech adv if too much upward force , which dislodges the weights and springs , the only way to get them back is to dismantle the other thing they do is seize up , either from a build up of crud and rust type stuff or the pins wear/springs etc wear .

Follow your manual if you intend to dimantle the dissy and mark anything to do with the Optospark and be very careful with the opto wheel they can be very fragile , the pommy made one is actually more robust than the Yank one .

Cheers

If you've had a point dizzy converted to breakerless ignition you may want to check that the arm that does the vacuum advance is connected to the base plate.

If I recall correctly, on my County there was a locating pin on the points that also made the connection between the base plate and the vacuum advance diaphragm.

A simple test to see whether it's operating is to connect up your timing light and as you rev the engine the timing mark on the pulley should move steadily away from the pointer.

Chris