<VV> timing changes at idle.

[Frank DuVal]

As Matt says, make sure the vertical port you are using does not have 
any vacuum on it at idle. Turn down the idle speed screw on this carb to 
reduce the vacuum at idle.

The vacuum advance trick you have read here is to use a hammer and deep 
socket to dimple the face of the VA unit, thereby increasing the spring 
pressure on the diaphragm. Another way to accomplish the same is to bend 
the tab on the other end, beside the actuating lever. Hard to describe 
in words, but have seen it demonstrated at club meetings.  This trick is 
to keep the advance from coming on too quickly.

First fix the vacuum at the port.

This is "ported" vacuum, which operates reverse of manifold vacuum. i.e. 
this port should be max vacuum at full throttle, and zero at idle. It is 
the vacuum above the throttle plate.

Frank DuVal

On 11/11/2011 12:25 AM, Mark Durham wrote:
> Gents, I've read here about doing something to the distributer vacuum
> advance to stop the advance from moving the timing at idle speed but
> cannot remember what was done.
>
> Today I set my engine rpm to 600, adjusted the timing with the advance
> hose off and plugged, reset the idle, rechecked the timing, then
> hooked the hose up, and the engine accelerated as the advance moved
> the plate a bit. What can I do to get the advance spring stiff enough
> that the timing stays stable at idle and will come in later as I
> advance RPM?
>
> Mark Durham
>