Ignition: Vacuum Advance bleed down

[kg.works]

'54 vacuum advance
Having some issues with jerky acceleration in 2nd and less in high.
Tested the vacuum advance with a vacuum pump and found it would bleed down.
I happen to have two new(NOS 50+ yr old) units which I tested.
They also bled down.
I'm used to vacuum advance units holding their vacuum.
Is this correct or do I have three bad units?
Thanks
Graham

[rkapteyn]

You are right.It should hold vacuum.
You can send these units to Dave Thibeault for installing a new diaphragm.

978 897-3158

[karterfred88]

Sounds like three bad units-sorry.

[tim333]

I have the same problem with a check valve for my 63 Hawk hydrovac.

[345 DeSoto]

What is the diaphragm made of?

[jclary]

Sounds like three bad units-sorry.

Well...bad units...IF...your tubing to your vacuum test unit is holding secure. Don't know exactly how your rig is set up, but unless it is clamped very tight, it could be the connection is leaking.

[kg.works]

Thanks everyone for your feedback. I'll send the two 'new' units to Dave for a rebuild.
Graham

- - - Updated - - -

Thanks everyone for your feedback. I'll send the two 'new' units to Dave for a rebuild.
Graham

[TWChamp]

To check for vacuum holding, I used to suck on the opening then stick my tongue on it to block the opening.
That was a quick easy check if you don't have a vacuum pump with gauge.