Testing distributor diaphragm

[ThinLizzy13]

I've been driving my 223 with the load o matic setup quite a bit lately. It developed very sluggish acceleration and a flat spot from about 45-50 up. After playing with timing, dwell, and testing every component it's finally come down to the distributor diaphragm.
As far as I can tell the vacuum line to it is working. I pulled the diaphragm and sucked air through it (no vacuum pump lol). The plunger barely moved and I could hear air whistling. I assume this means the diaphragm is shot? Or should I be checking it a different way?

[unibody madness]

best guess is the diaphragm is shot.

[Michelle]

I agree, you should be able to advance it by sucking on it.

[ThinLizzy13]

Thanks, one is on the way

[bruceandersson]

Yours is probably shot. I've always watched the timing as a connected the line to make sure it was moving. You also want to make sure the distributor plate is moving freely when you install the new diaphram. Some of the parts you get a truely old stock. For a diaphram this may not be good as the rubber deteriorates with age. Check the new one when you get it. I've sent a few back for replacement.

[64 f100]

I always put a fresh hose on the vacuum advance, then suck thru the hose until the advance works, then place my tongue on the end of the hose. Vacuum advance should hold steady and not retard if good, if leaking will retard back to where it started.

[ThinLizzy13]

New one checks out. Came from Mac's. Thanks everyone