I have a sbc 350 and i am having trouble with my vacuum advance. Every time i plug the vacuum advance into the distributor then run the motor the motor sounds like it is at a real low idle and might be misfiring. But when i plug the vacuum advance to time the motor the motor idles fine at 10 degrees advanced. I can't seem to find what is wrong since all i find is that the vacuum advance will add more degrees to the motor and should raise the idle instead of lowering it. Any ideas on the topic would be great.

btw i have a ported vacuum advance

If you are using ported vacuum, it should have no affect at idle if it is connected or not. Some other problem or more info needed.

Whats the idle RPM set to?
Use the timed port, there is no vacuum there at idle, if there is, then the primary throttle plates are open too far
What kind of carb?
If its a holley, check the power valve
Check your firing order, you may have #4 and #7 swapped
Did you install the distributor, they will install 3 ways; correctly, 1 tooth off, and 180 degrees out

TIMING 101
These Articles may Help ↓

PART 1 → http://www.elcaminocentral.com/showthread.php?t=27545

PART 2 → http://www.elcaminocentral.com/showthread.php?t=27544

PART 3 → http://www.elcaminocentral.com/showthread.php?t=27543

dont have a tach on it right now so i dont know what rpm i am at, but i could put it on tomorrow.. in the meanwhile, could there be something wrong with the carburator? i have an edelbrock carburator..

There is always the chance the the outer ring of the harmonic balancer has slipped, making the timing mark off. Maybe your reading isn't what it actually is, etc. Sounds like too much advance from what you describe. Back the initial timing off about 10 degrees and see how it runs that way with the vac line connected..........
That's assuming that your are using the correct port on the carb, and throttle closed.

If you are putting the vacuum line for the vacuum advance to the port on the carb that is pulling a vacuum all the time that is where your problem is because it is advancing the timing of the motor as soon as you connect the line. You only want the timing to advance under a load which the other port on the carb will do. Only under quick throttle response will that port pull vacuum thus advancing the timing of the motor so it will more effectively burn the additional fuel.

i only say all that because my uncle thought that he was smarter than me and put the line on that port on my motor when i was not paying attention. That was fun trying to find that when you just went through everything.

i tried both ports on the carburator to the vacuum advance on the distributor - both had the same effect.. i'll try to move the timing back 10 degrees and see if that makes a difference..

moved the timing back 10 degrees and plugged in the vacuum advance, the problem is still there.. it sounds as if it is backfiring out of the exhaust, and still is not on time

1 tooth off on the distributor maybe?
Craig (I used to be Tough and Ruthless....now I am rough and toothless)

in what direction do i put it one tooth off?

That might be the Problem here.
Don't take offense in this, but what is your BASIC KNOWLEDGE of Engines?
You don't put it one tooth off, it has to be right on.
NOT a tooth off in either direction, but right on.
It just may be to your benefit to take it to a Shop,
and Pay them to do a Tune up, and if done right, they'll check the
timing / Distributor to be sure it's correct.
Ask a Friend or Relative to give you a hand, someone that
knows something about Engines.
If you don't know the Basics, It will be too confusing for you to
understand any assistance offered in a forum type of setting.
Now, if I'm wrong in thinking that your knowledge is very minimal in this field,
I'm sorry. And it's not a BAD THING.
I know of NO ONE that was ever Born with that Knowledge.
Everyone that knows anything, learned it somewhere, at some time.
Pay the Mechanic the less than $100 and be sure it's right, and save the Headache for later.

I have a friend named Albert. He has installed every distributor in every engine that I have done for the last 20 years. It is now tradition but it came from the fact that I had never done it and he could do it right the first time. I still call him up when it's time to do one. My point being, that it might be a good thing to find an "Albert" to check out the distributor installation. Having someone checking it out will build your confidence if it is okay and if it isn't then it will help you to learn.
Craig

i have a general knowledge of engines, just never really messed around with the distributor too much.. people keep mentioning putting it one tooth off, which i dont really know how to do. would rather get some help figuring out how to do this myself than to take it to a shop.. any advice would be greatly appreciated, thanks.

Maybe the carb is loose and air is leaking in through the base gasket. I had that happen and it drove me nuts trouble shooting it.

OK Johan,
Lets get started then, I like it when someone wants, and is willing to learn.
The first step to this, is you have to be sure that your Motor is at TDC, (top dead center).
To do this, you need to bring your Timing mark up to the pointer on the front of the Engine, as close to "0" as possible.
http://i300.photobucket.com/albums/nn18/coyoteon2/miss/T1.jpg
http://i300.photobucket.com/albums/nn18/coyoteon2/miss/T2.jpg

Now then when doing this, you will have to be sure that the motor is on the Compression Stroke, and not the Exhaust stroke. For should you get it wrong, then you will be putting your Distributor in 180 deg. out. Not good.
Several ways to do it and find it's the compression stroke.
#1 ~ Remove the #1 spark plug, (also easier to remove all 8). Using a breaker bar / socket on the center Crank bolt, rotate your engine by hand clockwise facing the Motor.
With your Index finger over the #1 plug hole. as the piston approaches TDC on the Compression stroke, your finger will feel that Compression. IT WON'T IF ON THE EXHAUST STROKE. I should have said this first, good idea to disconnect the Battery to be on the safe side, prior to doing any of this.
Now then, while you read this to be sure your understanding what I'm trying to say, because explaining things in words ain't my best thing. I'll explain in the next post, your next step.

Still with me Johan ? OK.
Your next step to this, is to check your Distributor to see if it is off, or if it's dead on.
Remove the Cap and wires from the Distributor, now LOOK at the Rotor, the rotor should be pointing directly where your #1 spark plug wire plugs into the Distributor cap. If it is, you should be GOOD TO GO. If it points to before, or after, by very much, you could be 1 tooth off where it need to be.
Look at this photo ↓
http://i300.photobucket.com/albums/nn18/coyoteon2/miss/350_firing_order.gif
You will see the #1 plug on the Motor, if you look at the Distributor, you will see where the #1 plug wire should be, as well as where the Rotor should be pointing.
If that is NOT the way yours is, you will need to remove the Distributor, and re install it so that it is.
Now then, if this is the case, and you had to re install it,
your next step is you will need to unplug all the spark plug wires, then re install them, starting with #1 then the rest in the proper firing order. 1 8 4 3 6 5 7 2 , IN A CLOCK WISE ROTATION.
That's it my man, hook up the Battery, fire up the engine, fine adjust the timing with a light, and your good to go.
QUESTIONS ? I tried to be just to the point, and tried not to confuse. But HEY ~ What do I know? :dontknow:
Hope it helps, and hope you were able to learn somethin.:beer:

OH, sorry, Guess I should have asked first. It is a V-8 we are talking about here, right?
If not, ↓

http://i300.photobucket.com/albums/nn18/coyoteon2/miss/chevy_firing_orders.jpg

The procedure is the same, just the firing order, and layout
will be different.
Just thought I'd clear that up.:beer:(must be that dang Root Beer AGAIN):poke:

Real good post and pics Coyote, one more thing if I may add it. When you put the dist. back in the correct position, if it doesn't drop all the way down, hold it in place and have someone turn the engine over with the wrench or by just tapping the key until the shaft and oil pump line up. It will drop down then.

Another way, before dropping the Distributor in, take a long screwdriver, use it to reach down in the hole, turn the pump shaft to align with the #1 plug / cylinder, (as it's in line with the Rotor oreintation ) and the Distributor should and most likely drop ALL the way in.
But you did bring up a GREAT POINT ! I've seen people fool with trying to get the Distributor in for over an hour if not lined up.:secret:

thank you Larry for detailed instructions, I will give this a shot when I get off work. thanks again!

EDIT: take a look at my pictures if you want to see what I am working on :) LINK (http://www.flickr.com/photos/28374565@N08/sets/72157623360155953/)

I tend to agree with this fella, a man that developed these systems at GM.
http://www.elcaminocentral.com/showthread.php?t=17934&highlight=ignition+timing

thanks for all the help but it's still not running right i did exactly what you said and re-put in the distributor and made sure the timing was correct. the same problem occurs... when i run the motor with out the vacuum advance it is fine but when i plug it in the motor sounds like it is firing off. but i do have new information i feel like i might have narrowed it down to the carburetor. when i run the motor with the vacuum advance plugged or unplugged the carb seems like it is spitting back and there is something burning inside of it so now i'm stuck again. if anyone could point me in the right direction that would be great.

So.......what do you mean by "something burning inside of it" ?? Do you mean a bacon frying sound? Or was it actually burning ? Make sure the carb base is tight on the manifold, like mentioned here earlier.

It might be necessary to do a compression test, to make sure you don't have a valve problem. The "spitting back " could be a valve problem, or a lean mixture problem..

no flames or bacon frying sounds - but there was some smoke and you could smell it too.. the carb base is tight on the manifold.. also just discovered that one of my spark plugs were cracked, not sure if this could be related to the problem though..

Are you connecting the vacuum advance to a port with manifold vacuum (i.e. vacuum present at idle)? If so, the RPM should increase due to the additional timing advance. If it starts acting up at that point, try disconnecting the line to the carb and applying vacuum from an outside source to the advance unit and see what happens. If it acts up then, you have a timing issue. If the RPMs increase from the additional advance, then the advance unit is likely OK. If the timing does not change, then you likely have a bad advance unit. Your symptoms indicate to me that you may have a leaking vac advance.
Bill

adjusted the mixture and fired her up again, this time without the air cleaner on - a foot long flame shot out of the carb! any ideas?

Its OUT of time, You have a bad timing gear set probally jump a couple teeth, the valve timing is off:nanawrench:and your igniton timing is right,

That sort of sounds like a cross-fire. Did you replace the distributor cap? If not, a carbon track in the cap may be a problem, like cross firing to a different cylinder.

Hope you replaced that cracked spark plug.

Doug

Is the distributor used. One of the wires to the pick-up coil could be broken inside the insulation. Would cause a miss or kill the engine when the vacuum advance was pulled in.

Burns, you got a timing problem and now is a great time to learn; Do 2 things; Check your timing pointer for top dead center w/ a piston stop then time to 18 deg with a lite; #2, get someone there
to help you.

thanks for all input, heres what we have done since last post; changed the sparkplug, took out the distributor and redid all the sparkplug wires and retimed it, checked for vacuum leaks and checked the settings on the carb.. she runs fine when the vacuum advance is plugged, once we connect it, the engine dies. wondering if i should give up and have a professional take a look at the distributor, or if i should simply drive the car without the vacuum advance?? any input?

The diaphragm in your vacuum advance module might be ruptured and causing a vacuum leak and not activating the advance lever in your distributor. You can check it by sucking on the hose and see if the diaphragm activates the lever with the cap and rotor removed.

retarded the distributor ALOT and got her running with the vacuum advance hooked up. took her out for a short drive, and she is hesitating when i hit the throttle, especially from a stand still. parked and let her idle when the car suddenly died. at first i thought i ran out of gas (my gas gauge is not hooked up so i cant really tell, but i know im low), but she wont even turn over. tested the battery and there is plenty of juice in it, but nothing going out to the rest of the car; starter, lights, horn arent getting any power. all the wires and grounds that i can see look fine.. any ideas?

check the fuseable links/conections at the starter and the pos/ground cables....

as for the timing,,have you checked your total timing,,with vac advance connected,,
see what kind a spark curve u have ??? the advance stop may not be working ,,,
and some are adjustable...:texas: