Is this normal? (distributer vacuum)
Thread Starter
Instructor
Joined: Aug 2001
Posts: 150
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From: Jacksonville FL
Is this normal? (distributer vacuum)
I recently became aware of a vacuum leak in my '77's distributer vacuum module thingee. There is a small hole on the bottom of the silver can that the vacuum hose is connected to. Is this supposed to be there? When I plug the hole there seems to be little difference, in fact, the idle gets rougher. Any thoughts?
Thanks,
Ted
Thanks,
Ted
Moderator
Joined: Jun 1999
Posts: 7,117
Likes: 51
From: Dove Mountain Arizona
Re: Is this normal? (love to drive)
Go get a new one, around 12 bucks. Little hole, methinks yes it should be there. Need some relief for the bellows to move at all. What happens if you just plug the hose? If no difference then your leak is elsewhere.
Burning Brakes
Joined: Dec 2000
Posts: 1,183
Likes: 2
From: Des Moines Iowa
Re: Is this normal? (love to drive)
With engine running, at idle, is there any vacuum you can detect at the hole? If yes, then suggest you replace the vacuum canister, if not, then believe it's OK, so long as it is working, in that you do get spark advance as vacuum increases.
Thread Starter
Instructor
Joined: Aug 2001
Posts: 150
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From: Jacksonville FL
Re: Is this normal? (john's '81 mouse)
There is vacuum at idle...quite a bit actually. I notice a bog sometimes when letting off of the gas while cruising and reapplying the gas. I plugged the hole last night and noticed a "spike" in my power band where there was none before. At around 3500 the engine feels like it has nitrous injected. (not that powerful but the same feeling) What I'm trying to figure out is if the hole has always been there or if I knocked it when adjusting the timing one time? Also, plugging the hole did not fix my cruising bog problem.
Thanks,
Ted
Thanks,
Ted
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Is this normal? (love to drive)
When you suck on the hose to the vacuum advance control unit, it should not leak, and it should hold a vacuum. If it leaks, you just gotta' replace it. Recommend you replace it with NAPA part number VC1838. This will produce a perfect combination with a properly set up mechanical advance curve.
Thread Starter
Instructor
Joined: Aug 2001
Posts: 150
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From: Jacksonville FL
Re: Is this normal? (lars)
Well...I found out that the hole on the bottom of the canister is supposed to be there...but the vacuum leak is the result of a bad diaphram(original equipment is getting pretty old) I just installed the new canister today and I notice that I have much more advance than before...but my idle still jumps around...up and down within 100 rpms. I thought I got all of the vacuum leaks but maybe not. Is there anything else that would cause this RPM fluctuation at idle?
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Is this normal? (love to drive)
Maybe the little hole is to let condensation drain out so the thingy doesnt rust out. Or maybe it could be for different atmospheric pressure situations. If it were sealed then atmospere could have an effect on it.
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Thread Starter
Instructor
Joined: Aug 2001
Posts: 150
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From: Jacksonville FL
Re: Is this normal? (Jvette73)
Hey that doesn't sound entirely impossible. I seem to have a rougher idle than before...is it possible that my timing is now over advanced at idle? The rest of the ride seems smoother than before. I retarded my timing back to stock specs - 8 degrees at 500 rpm w/no vacuum advance. When I hook the vac advance back up the timing shoots up to ~18-20 degrees.
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Is this normal? (love to drive)
If you hook up the vacuum and the timing increases then the canister is working. Like lars said, mechanical advance curve is important. Rough idle could be associated with other things. Change plugs lately?
[Modified by Jvette73, 5:18 PM 12/11/2001]
[Modified by Jvette73, 5:18 PM 12/11/2001]
Thread Starter
Instructor
Joined: Aug 2001
Posts: 150
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From: Jacksonville FL
Re: Is this normal? (Jvette73)
Plugs were changed not too long ago...the engine has 150k miles on it so I guess I could be asking too much...never been opened up for a rebuild or anything. I seem to remember there being low compression in one of the cylinders...I suppose this is where the bulk of my probs are originating from.
Before, when I had a leaking vac. canister, I would have a bog when I punch it off the line...now that bog has gotten worse. I'm gonna start increasing my timing a degree or so a day and see if it makes a difference. I've still got this feeling that there's vacuum leaking somewhere still...
ahhh well
Ted
Before, when I had a leaking vac. canister, I would have a bog when I punch it off the line...now that bog has gotten worse. I'm gonna start increasing my timing a degree or so a day and see if it makes a difference. I've still got this feeling that there's vacuum leaking somewhere still...
ahhh well
Ted