vacuum advance question
 

I have '65 coupe, 289 auto, 2v. While doing timing check with strobe light, I noticed no difference in timing mark whether vacuum advance was plugged or not. Is this normal? I checked to see if any other ports were open but only port I see is what manual calls "choke cleanout". Is this supposed to open as it is on my car, or is it supposed to be capped or something hooked up to it. Thanks

RE: vacuum advance question
 

I dont think thats normal.
You should notice it begin to advance as RPM climbs I believe 13 to 14 degrees of advance is normal if your not getting any advance then it aint working.

Not sure about that choke clean out.

-Gun

RE: vacuum advance question
 

well the distributor works off of timed vacuum, so at an idle there is no vacuum being pulled anyways. in theory you could hook the vacuum advance up and at an idle it wouldnt change - or you could unhook it and leave it unplugged (creating a vacuum leak) and it wouldnt change the engine rpm because at an idle that port isnt pulling vacuum anyways

RE: vacuum advance question
 

Mine didnt change last I remember. I switched to non vac dist. years agao.

RE: vacuum advance question
 

At idle, you should get pretty much zero vacuum at the vacuum advance, so you shouldn't see any significant difference between having it plugged in and not.

RE: vacuum advance question
 

You may want to check the vacuum advance diaphram itself. After 40 years the rubber gets very hard and brittle. A pretty cheap fix too. I had the same problem. Found it by hooking up a hand vac pump and watched the timing marks with timing light. When I added vacuum no change in the marks. Only then did it dawn on me the diaphram could be bad.

RE: vacuum advance question
 

yeah, and adjustable ones are fairly cheap. of course, its a great excuse to buy an upgraded model from crane, mallory, accel, or msd. ;)

RE: vacuum advance question
 

have a 289 with autolite 2110 (2 barrel). same here. the vacuum advance does nothing at idle and it's supoposed to be that way.

as my77stang states: timed advance.

To test sure your vacuum advance works:

- switch off engine
- remove distributor cap
- remove the vacuum hose from carb to vac advance on carb side.
- suck on the hose (i know it sounds disgusting)
- you should see the arm of vac advance moving the plate the points sit on (on HEI the same, just no points)
- when you have so much vacuum that the plate is moved as far as you can get it with sucking on the hose:
- use your tounge to block the hose
- you should feel the diaphragm pull and the plate should stay in same position.
If it moves backward and loosing the vacuum then your diaphragm is fried
the same if you keep sucking on the hose and the plate moves back and forth (loosing the vacuum).

if you're leaking vacuum there you'll need a new vadc advance. But check the hose itself as well.

if all is good then put all back together.

when you strobe the engine you should see a clear difference on:
- where does the timing mark go on revving up the engine without advance connected
and
- where does the timing mark go on revving up the engine with advance connected

kalli

RE: vacuum advance question
 

You have to be careful when that diaphragm is broken, on occasion a stray spark from the distributor housing may be sucked up and drawn into the carburetor, through the vacuum hose, resulting in total destruction of the vehicle by explosion.










Not really..:D:D.... but,,,

I have heard a story where air fuel mixture was being drawn into the distributor upon shutting the engine off. This resultwas a perplexing issue for the car owner. Often when the owner started his car, the distributor cap would remove itself from from the distributor base with a moderate popping sound.........

RE: vacuum advance question
 

Lol, that's cool, never heard of that one:)