924Board.org

[SportsPurposeGarage]

I have a 931 with the dual vacuum (non ditc) setup. Engine is fresh. starts and runs well. I am having a problem with advance/retar. car is a turd down low and although it shows boost and the afrs are dropping into the 11s, it just feels like a slug.
I have verified vacuum routing per the factory manual, with one difference being that my throttle body has a port in front of the blade that provides ported vacuum and one behind that has full vacuum. When I got the car position 1 was hooked to the ported vacuum and that's how i left it after the rebuild.

I set timing to 5 degrees with the hoses on, disconnected and plugged hoses and ran it up to 2k rpm. I get 20 degrees advanced, good per manual.

I hooked up a vacuum pump to position 1 and gave it 250mb and i get 33 degrees of advance, good per manual.

With everything hooked up, however, I can run it to 2-3k (stationary, no load) and never see more than a couple of degrees of advance

So I pulled the position 2 hose and the idle and timing jumped. The retard side of the dashpot is pulling about 15 degrees of timing out of the engine, even at idle. The vacuum signal to #2 at idle is 350mb (compared to 250mb on position1 with full vacuum or 0 with ported)

I have tried to swap signal hoses around, swap the signal from ported to full vacuum, etc, and essentially the vacuum advance isnt working or isnt overcoming the retard signal.

My expectation would be that the dashpot vacuum signals cancel each other out, you set base timing and then advance happens like a normal car (combo of centrifugal and then vacuum at idle/cruise) and then when boost starts and vacuum drops, the dashpot pulls away up to about 8 degrees of timing from the max of 32-38. But I can't get this to work as i expect. If the diaphragm was smoked, I dont think I would get any reaction on one or both sides of the dashpot with a vacuum pump but both seem to react to 250mb..
Any insight or help would be greatly appreciated!

[SportsPurposeGarage]

Does anyone have a vacuum gauge that can give me the readings from the signal hoses at the dizzy?

[morghen]

Did you replace the mushroom looking thing (actuator) on the side of the ignition dizzy?
Cam timing is on point?

Regardless, if you want a nicer running and fresher feeling 924, i make and sell a bolt on EFI kit for them.
_________________
Supercharger and EFI kits
https://www.the924.com