73 / 350 Auto. I have a slightly fast idle (900-1000) and suspected a vaccum leak somewhere. I started pulling hoses to see if I could find the leak point. When I pulled the vacuum advance hose the idle dropped down where it should be. Is this normal or do I have a distributor problem? I have not pulled the distributor cap for a closer look. Any thoughts?

Thanks

 

It's normal. When you disconnected the vacuum advance, the thermal efficiency of the combustion dropped like a rock. Find the idle problem, and then be sure to run with the vacuum advance canister connected.

 

If you would hook the distributar up properly this wouldn't happen.
Unplug the vacuum advance, then time the car to 12 degrees at idle and 36 degrees at 2500 RPMs, then if you have to hook the vacuum advance up, then find a vacuum that ONLY PULLS vacuum when giving the car gas.
Just start putting your finger over vacuum ports on the carb at idle and if your getting vacuum at idle thats the wrong one!
There should be a port on the drivers front of a Q-jet, that when you give the car gas, you will feel a vacuum, but at idle you will feel no vacuum.
Otherwise if you hook up the vacuum advance to a vacuum at idle sorce you have to adjust everything to that, but chances are it will idle high then when you disconect it or it falls off or rots in to, the car is going to quit right where you sit!
I leave it unhooked myself and don't have to worry about it.
If you PM me I will explain in more detail if you can't get it fixed.

 

that is correct only if you are more concerned with running the car to pass emissions testing at DMV rather than driving the car.
You are recommending that he hook up the vacuum advance to the ported connected and that was done ONLY because of emission requirements- no other reason whatsoever.
By removing the vacuum line off the canister and seeing the idle drop means he is already connected to full manifold vacuum which is almost always better for overall performance, better idle characterisics, better fuel economy, and lower operating temps.

 

I'll stick to my original statement, my car idles perfect at 650 in gear,
12 degrees at idle and 36 at 2500 RPMs how can I be wrong, isn't this combo what everybody is shooting for?
Or is there two different 12 degrees at idle and 36 at 2500 RPMs???
Also please speak in normal english if you would?

 

I agree with this. EVERYONE needs vacuum advance. Running only 36 degrees or even less if cruising at low speeds is retarted.
You need about 52 degrees to burn properly at cruise throttle positions. You also need a lean mixture to get better gas mileage, prolong ring/engine life and keep from fouling plugs.
I repeat everyone needs vacuum advance. No exceptions for a street car.
Also it is normal to pull the vacuum line off, plug it temporarily , set the timing and then plug it back in and adjust the idle back down to a reasonable level..
Vacuum advance keeps the motor idleing crisper and ported vacuum adds nothing to the idle or keeping the motor clean

 

There you go, confuse the hell out of them!!!!
So your telling me that when I use a dial back timing light, I should set it on 52 degrees and rev the engine to 2500 rpms and I should be at 52 degrees???
"I" know what your saying as mine is 22 and 36= 58, but without a dialback you can't know this info.
I think not.
Why would you say anything like that????
You might has 52 total advance adding up idle and advance but not just advance.
There are 3 ways to get advance.
1:ported
2: non ported
3 : no vavuum at all
How ever someone want to run it and what they think runs best is what they should pick.
My friend a machinist and the owner of a spitzer series and Jegs quik 16 shootout rail which has ran as fast as 4.48 in the 1/8 and normally runs 4.50s says don't use any vacuum and I'll go with his opinion.
I myself have worked on cars for 25 years so Im pretty sure,although there are several ways to do it, mine is equelly as correct and will run as good as any other way.
I do not like the idea of my idle relying on vacuum to keep it high enough to keep the car running.

As you will notice Im not hooked up and won't be!

 

How can you compare a rail to a street car????

The rail I used to work on had a magneto with the advance locked out. Would you run that on the street if someone told you to?

 

Sorry guys. Didn't mean to start a battle. Let me focus on the timing and see what I can find. The car runs great as is. I just don't like shifting into drive with the high RPM's. Thanks.

 

what is so confusing?
disconnect the vaccum advance line and plug it. set correct idle speed and set timing for 12* initial and 36* total timing. Reconnect the vacuum advance line and readjust idle to correct level. Now with the vacuum advance reconected total timing at approx 2800-3000rpm will be between 50-52* depending on the vacuum advance unit you have.
This is not a difficult concept.

As already mentioned, ALL street cars benefit from running a vacuum advance system. Race cars don't use vacuum advance because it would be useless since they are either at idle or WOT and not usually anywhere inbettween and at WOT there would be virtually no vacuum to run additional advance anyway.
you have been going on the fact that your car you run without vacuum advance on all threads that this topic comes up and while it works it's not the best set-up for a street driven car and by "pushing" the idea of running without vacuum advance and/or running a vacuum advance connect to a ported versus a full manifold vacuum source you continue to pass along incorrect information. Regardliess of having worked on cars for 25 years you seem to hace this particular information wrong which unfortuately is not all that uncommon either. I've had mechanics work on my car that plug the vacuum advance line saying it's not needed and that is the same incorrect mistake but it doesn't make it right.
On the other and, I suppose you could be right and others such as Lars, John Hinckley, Duke Williams, and other true experts and other actual automotive engineers and engine management specialists that I've spoken to are all wrong.....

 

Thanks BarryK. Alot of so called mechanics really don't know what they are talking about and are only parts replacers.
Find me an article that recommends disconnecting the vacuum advance for the street.
Read Lars paper. It is just one of many recommending a vacuum advance setup.
Guys I repeat EVERYONE needs a vacuum advance.
And we can NOT compare a dragster to a street driven car.
Notice I am hooked up

Opps have to take my word for that.

 

Norval, I don't claim to know a lot or be an expert on ANYTHING, but one thing that's I've managed to learn out of necessity because of lack of decent local mechanics is how to do timing and the vacuum advance system. Plus I've read enough and spoken enough to people like Lars, John Hinckley, etc to learn and to do my own cars so I'm confident of the information I've learned and from playing with it on my cars.
As you say........find an article anywhere that actually recommends disconecting the vacuum advance on a street driven car. I sure never came across any.
BTW, can't see yours hooked up because of that huge, beautiful blower!

 

Stick to your original statement if you wish. Your exhaust valves and the rest of the forum say you're wrong, however.
Regarding normal English, excuse me, that is normal English. Perhaps I'm used to conversing with more technically schooled people than you are, but I can re-explain it to the technically challenged if you wish. Just ask.

ps: What is this 3600 at 2500 RPMs you keep repeating?

 

So you shouldn't follow the instructions of a drag car owner, because your working on a street car?
But yet its OK to add aluminum intakes, quiker timing, headers ETC just like a drag car but can't take advice from a drag car owner?
Sounds to me like you just want to pick and choose what you want to hear?
Yet you take advice from so called "rocket sciencetist" and their book theriories, but not an actual person who works on them everyday?
I'll listen to a doer and not a sayer anyday!
Again I will not rely on a vacuum hose hooked to a idle vacuum sorce to keep my car running, and when you unplug it the car dies because of no idle, thats stupid!

 

I'm not even sure how to respond to this statement.

If you are implying that the above mentioned experts are solely sayers and not doers, those are pretty strong (and incorrect) words.

If you unplug your fuel line, your engine will die. If you unplug your distributer, your engine will die. I'm not sure what your point is here. It's stupid to run idle vacuum just because when you unplug it the engine will die? Is that the only consideration? The benefits of idle vacuum far outweigh this "inconvenience."

 

]So you shouldn't follow the instructions of a drag car owner, because your working on a street car?

That's right. A drag car runs a completely different setup. Way richer fuel mixture, alot more compression and only operates at high rpm.


But yet its OK to add aluminum intakes, quiker timing, headers ETC just like a drag car but can't take advice from a drag car owner?

The intake, headers, cam can benefit the street car as well as a race car because they let the street car breath better but the tune up is still different between the street car and the race car.


Sounds to me like you just want to pick and choose what you want to hear?
That's right because the two cars again operate under different conditions
Yet you take advice from so called "rocket sciencetist" and their book theriories, but not an actual person who works on them everyday?
A mechanic might work on cars day after day but what does replacing parts all day have to do with tuning a carburated street car?? Most of a mechanics life is just replacing parts.

I'll listen to a doer and not a sayer anyday!
I certainly am a doer, make most parts on my car in my own shop. Even make my own brakes from solid stock. Even turned my own super duty rear axles inhouse.
This has nothing to do with you or your mechanic saying vacuum advance is not needed on the street.


Again I will not rely on a vacuum hose hooked to a idle vacuum sorce to keep my car running, and when you unplug it the car dies because of no idle, thats stupid!
The only stupid part here is not running a vacuum advance on the street.

 

I Have A 73/350 W/auto. I Set My Timming To Factory Specs After Adding New Q-jet And Performer Intake With The Vacume Canister Hooked Up To Ported Vacume Port On Carb. I Does Idle Lower This Way But Off Idle Performance Suffers W/ A Dead Spot. So I Leave Mine Hooked Up To Manifold Vacume

 

To gain the advantages of a vacuum advance at idle you need it hooked to manifold vacuum. Port vacuum doesn't help the idle, only cruising. Stick to manifold vacuum.

 

If you have to rely on manifold vacuum to get past a dead spot, then your only masking a problem.
But hey duct tape hides the crack in a windshield also.
Its OK I one time took "lawn mower gas" and put it in my car to get to the gas station to get car gas!!!!

 

Ah the ported vs. manifold debate.

1st of all to the original poster, sounds like you got the vacuum advance hooked up right and your car is acting as expected with the vacuum advance disconnected. If you want to lower idle RPM (sounds like that is your concern) simply lower the idle speed at the carb.

I have mine hooked up to a ported source myself - the reason being my timing is set at the proper and desired starting advance already (16) and, with my idle vacuum with the cam I have, my timing and RPM would bounce around like a ping pong ball as it would never be all "in". So ported works for me.

I would have to get a new vacuum can that brings in all the advance at a lower vacuum for manifold to work, not sure if there would be any benifits. But I agree vacuum advance is benificial for a street driven car. Also, and I am not sure if it's a material issue at all, I never liked the tought of advance diving down (as a result of vacuum decreasing) for that moment as you enter WOT from idle.