Timing help please

[mikey]

To achieve tickover and driveability I have opted to advance my cam 6 degrees. The cam is a Crower 427 witi 260 intake duration and 266 exhaust duration.

Vacuum at Tickover (900 RPM) has stabilised better at 11 in/HG (it was 8-9 flickering ansd there seems to be a better vacuum at cruise.

Re-set the timing to compensate for the cam advance. 18 degrees at tickover (vacuum to distributor blocked off) and 32 degrees at 3000 RPM (wanted 34 to 36 as I had fitted the black 18 degree bushing, but anyway).

Problem is when I fit the vacuum to the distributor, its running 50 degrees at 3000 RPM. Obviously the total timing is being increased by the vacuum advance even after a point when I thought it should have stopped.

Have I missed something obvious. I want the vacuum to bring the advance in quickly at tickover and light cruse, but I thought it should have stopped contributing at 3000 RPM.

Your help would be much appreciated as I am getting to the edge of my abilities in understanding the problem.

In anticipation - thanks guys

Mike

I have heard of people not running with vacuum - is this the reason why.