View Full Version : vac. advance?
09-08-2000, 04:38 PM
how much vac. should it take to just start moving the pickup coil in the dis. and how much vac. to be at full advance? seems like if I suck on the hose mine takes almost all my might to move it. I also have tried this at a few junkyards and they were the same. is my vac. advance dirty or what. it has no leakdown. I thought 20 mmhg was full gas. that seems like nothing compared to what it take to move the advance
09-09-2000, 02:36 AM
I don't think that lungs develop alot of vacuum. I found that the diaphram in my vacuum advance doesn't hold vacuum but noticed that the spring return is quite strong. I would think it is that way to return the advance quickly in response to changes in engine load.
Make sure that the plate holding the pick-up in the distributor moves freely (clean and lubed) and things should be ok.
Check the timing with a timing light (preferable with a dial adjustment to zero the light) and check to see the difference between the timing advance with and without the vacuum advance connected.
According to the charts in the FSM for an 84 show vacuum advance starts at about 3-4 inches of vacuum and maxes out at about 12 inches of vacuum.
09-10-2000, 01:28 PM
<BLOCKQUOTE>quote:</font><HR>Originally posted by reddog:
I found that the diaphram in my vacuum advance doesn't hold vacuum but noticed that the spring return is quite strong. I would think it is that way to return the advance quickly in response to changes in engine load.
I recently did the whole ignition upgrade found at: http://home.off-road.com/~ifsja/tech/electrical/ignitionupgrade.htm
This included replacing those advance springs in the dist. with 'weaker' springs. Which gives you a faster advance time.
09-11-2000, 04:03 AM
Well after reading this thread I had to go pop the hood open on my 88 and get out my little Mightyvac II.. like a spray bottle or a pistol with a vac gauge on top.. First of all I can pull over 20 inches of vacuum with just my mouth.. and my vac diaphragm for the advance, definatly holds vacuum. You were correct reddog, it starts moving around 3 and tops out mechanically around 12(wether thats as far as it goes or thats as far as the linkages lets it move ). I would say to anyone that has a diaphragm that will not hold the vacuum that has been applied to it has a bad one.. Hope this helps.. it certianly would help to have this working correctly.
88 Grand Wagoneer
Warn 20990 Lockouts
NP 229 (Funky)
Custom Hacking Via S.P.A. (Standard Polish Archetecture)
09-11-2000, 09:30 AM
Hey, you guys who are measuring your, um, er, oral vacuum capacities, this is not that kind of web forum!
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