Vacuum advance question

[Stallion]

Okay, my vacuum advance on my distributor had been mysteriously disconnected. I don't know how the advance went, and that's what bothers me.

So I was just outside and I decided to put the vacuum hose on the actuator on the distributor. All that happened was the raise in RPMs as opposed to disconnection.

For instance, without the vacuum advance, I would idle at 600 RPM. But connected, it would idle at around 850 RPM. Isn't that kind of high?

So what do you think? :confused

Thanks!

TR

 

[MaineShark]

If the idle was set after the advance was disconnected, then it will not idle correctly with teh advance re-connected. You'll need to re-set the carb after the advance is fixed.

Joe

 

[Bob Chadwick]

Check out Lars recurve kit for your distributor. My computer crashed and I lost his emai but I think it comes with a new vacuum unit and the items necessary to produce more power.

 

[Stallion]

But I just don't understand, why would the previous owner want to disconnect this vacuum advance!? :confused

 

[Scooter76]

Get the vac advance fixed. Your gas mileage will go way down. This is one of the main purposes for vac. advance. Rule of thumb, set your initial timing to specs. with the vac. advance disconnected & hose plugged. Then set your idle speed with the vac advance hooked up.

 

[Bob Chadwick]

Mine was disconnected because it didn't work.

 

[Stallion]

Mine was disconnected because it didn't work.

Why didn't it work?

Get the vac advance fixed. Your gas mileage will go way down. This is one of the main purposes for vac. advance. Rule of thumb, set your initial timing to specs. with the vac. advance disconnected & hose plugged. Then set your idle speed with the vac advance hooked up.

How would I do this? What would be the procedure to get the advance back up and working? Any help on carrying this out?

Thanks!! I appreciate it.

TR

 

[Bob Chadwick]

I don't know what it didn't work. I had the carb replaced and came back for it and was told that the vacuum advance was not working and that they replaced it.

I don't know how you would check to see if it is working. I vaguely recall as a kid sucking on a hose connected to the unit with the car off and the distributor cap off and monitoring to see if the unit advanced. Obviously not precise but perhaps it is a starting point.

 

[Jack]

TR:
First check to see that the VA can is any good: Take the dist cap & rotor off ... connect about 2 feet of NEW vacuum hose to Vac can .... suck on hose and look to see if you see the VA can pulling a lever in dist. If it moves that's a good sign ... then suck on it and get it to move ... then block hose w/ tip of your tongue ... look to see if the lever slowly returns back to initial position ... If it returns while you're holding a vacuum the vac can is junk.

Summary:
If the vac can lever don't move while under vacuum ... the vac can is junk because it has a large leak.

If vac can lever returns to intial position while under "stable" vacuum ... the vac can is junk because it has a small leak.

If you need a new vac can:
From Lars paper ... go to NAPA ... get vac can NAPA P/N VC1838 ... Lar's suggests this can for best all around performance. We recently used that one on a mildly cammed '82 Suburban ... works great!
JACK:gap

 

[Stallion]

TR:
First check to see that the VA can is any good: Take the dist cap & rotor off ... connect about 2 feet of NEW vacuum hose to Vac can .... suck on hose and look to see if you see the VA can pulling a lever in dist. If it moves that's a good sign ... then suck on it and get it to move ... then block hose w/ tip of your tongue ... look to see if the lever slowly returns back to initial position ... If it returns while you're holding a vacuum the vac can is junk.

Summary:
If the vac can lever don't move while under vacuum ... the vac can is junk because it has a large leak.

If vac can lever returns to intial position while under "stable" vacuum ... the vac can is junk because it has a small leak.

If you need a new vac can:
From Lars paper ... go to NAPA ... get vac can NAPA P/N VC1838 ... Lar's suggests this can for best all around performance. We recently used that one on a mildly cammed '82 Suburban ... works great!
JACK:gap

Where exactly is this Vac can? Is it right under the distributor cap?

Okay, I will do this test. But, what would this tell me? If it is actually gone bad, what would this do to the vac advance on the distributor? And if this is good (the lever doesn't come down), then what else would I need to do to get my vac advance back up and working?

Thanks!!

TR

 

[Bob Chadwick]

You will need to replace it and hook the vacuum line back up to it.

 

[Jack]

I decided to put the vacuum hose on the actuator on the distributorTR

TR:
As before ... take off dist cap & ROTOR ... DO NOT loosen nor remove your distributor ... the vac can is the "actuator" you referred to above. Held in by 2 screws and a bent rod ... very quick & easy to replace ... & cheap too (under $15). It is normal for them to fail/leak after many years. Again ... use NEW vacuum hose ... it's cheap. While you're in there ... blow the whole mess out w/ light dose of aerosol brake cleaner IMMEDIATELY followed by strong blast of compressed air ... then lightly mist it all with some WD40 ... then replace vac can, cap & rotor. Brake cleaner burns eyes, skin, some plastic & rubber ... hence immediately.
JACK:gap

 

[mvftw]

Stallions idle is correct at 850, look at your emission sticker. '78 L82 4 spd calls for 900, I know he has a L48, should be close. So leave the hose on...

 

[Stallion]

Okay, Jack. I'll do this test as soon as I get new vac hose for that. But why would I need to take the distributor cap and rotor off to do this? If this vac can is the actuator that I'm talking about, it's pretty easily accessed. Or do I need to take cap and rotor off?

Stallions idle is correct at 850, look at your emission sticker.

Hmmm...I have no idea why the previous owner would disconnect the vac advance. I think I might give him a little call. But he was one of those guys where he had a mechanic that I'm sure did pretty much everything. But he might know. Although, if you sell a car, would you really want the buyer to bother you about something like this?

Thanks for the input, fellas.

TR

 

[Jack]

TR:
In order to access the vac can's attaching screws & rod ... you MUST lift the cap away from dist ... removing rotor will help.

NOTE: the round, tapered, conical part of vac can that hose attaches to is readily visible ... much of it hangs outside dist. But it is attached to & screwed to INSIDE of dist ... I promise.

Just a suggestion: Don't bother PO about something so petty. He probably doesn't know/remember anyway & it really don't matter. It could've fallen away & nobody noticed or didn't know where to re-attach. Some mis-informed folks have heard "It'll run better w/ vacuum disconnected" ... wrong! Just fix it.
JACK:gap