Vacuum advance problems

Just getting some opinions and theories. According to Edelbrock there is supposed to be 1 ea. full-time and timed vacuum advance port on their carb. However, I have two 600cfm carbs of theirs and when I hook up the hose to either one of the ports on both carbs it shoots my advance up by 20 degrees or so at idle. I was wondering if Buicks run constant advance or is there maybe something wrong with my carb or the advance diaphragm(spelling correct?) on the distributor? Let me know what you think and what you would do please. Right now I am just running around with it disconnected totally. Thanks.God Bless the USA!:TU:

 

an excellent opportunity

My wild guess:
The idle is set with to much open. This will activate timed vacuum.
Check the timing (and adjust if not right, late timing calls fore more idle screw in ) then readjust the idle setting.(both the mixture screws and idle speed/butterfly/throttle opening screw) This most likely will cure the problem.
If your camshaft is of the more radical type, this is not an uncommon condition.
If so this can bee fixed. However, I am not the best to explain how to do it (involves drilling a small hole in the butterfly. There other people here on the board that can guide you through this if it is what it takes.
.
On the other hand, if youre happy with the performance of the engine and cant find carb or timing miss setting. And you cant find a ported vacuum source.
This is an excellent opportunity fore you to start use full vacuum with limited movement the way Ignitionman suggests. I got only positive things to say about using this method.
Lars :TU:

 

I'll just add all this,

On Deadbroke *Edelbrock) square bore carbs, as you look at them from the front of the vehicle/engine, will have a FULL MANIFOLD vacuum port on the front of the carb, driver's side, and a PORTED vacuum port on the pass side. The PORTED port will be slightly higher than the FULL MANIFOLD port on the carb body.

I agree with Larry, throttle plates too far open, possibly by having a carb base gasket support issue at the carb pad on the manifold. Pull carb and take a look at the inpressed portions of the gaskets, the patterns made by the carb and pad. See if there is a place the gasket isn't supported by the pad and allowing a leak. If leak, use EgoBleak (Edelbrock) p/n 2732 plate and two gaskets.

Also, when the vacuum advance is limited as Larry says, and actuated with manifold vacuum, the throttle plates will usually need to be much farther closed than in any other tune condition, so that should help in shutting the ported port off at idle and getting the whole gooey, sticky mess back to working right.

 

Thanks for the responses so quickly. Yes IgnitionMan I see when I took the carb off on the front two intake holes there is a quarter to half inch deep passageway between them,looks like it connects them together, where the gasket doesn't sit in, it just hangs above it. What is this due to? Did OEM carbs sit down in that gap? Will that plate your reffering to cover that gap or what does it do? While your at it. I also have another question that could be causing it also. When setting idle and timing(2 1/2 BTC according to my sources), do I set them in drive? I notice if I set the timing in park when I have it dropped in drive the timing backs off significantly.I am learning all this from scratch from this car. Thanks.

 

I know this happens on quadrajets, but I'm not sure about yours. They will draw vacuum at idle from the ported source if you start them cold and the choke engages the high idle. After the warm-up period and the idle kick down, it will return to vacuumless at idle.

 

Ignnitionman is taking about a place not sealed properly... are you missing a exhaust heat port blocking stainless steel plate under neat the carb? The 340 is not my strong side..... so im not sure if its suposed to be there in the first place....Larry70gs?
Lars

 

don't go wild!!

No the OEM carb. did not sit down in it(the gap)!
stupid ME!:spank: Ignitionman IS also talking about a platebut I believe not the kind that was on my mind.
This passage of yours, is the place where the vacuum pulses from the two primary ports/ hols is smoothened/ made more steady so there carb and the other vacuum operated things will se/ feel a more stabile, less pulsating vacuum. It IS supposed to bee that way. Dont fill it up with anything.
Dont go wild with the sealant; apply a thin layer on the flat surface on the intake, then a thin on until you reached the carb.
Btw. Is your distributor stock/oem?
and what initial timing?
camshaft?
Lars

 

Do most people seal up the the carb gasket? Yes my sorry dead tired distributor is stock,old and wore out too. As far as initial timing goes I don't know what you mean other than when I put the crank and cam in the motor they were installed at TDC perfect and the distributor set to fire no. 1 at 2 1/2 degrees before TDC. My cam I am not sure on. The guy I bought the car from said the cam wasn't that old but didn't say whether it was stock or not.

 

I agree with Larry.
Sealant only if (as I-man wrote), the impressed portions of the gasket shoves a need for it. (air leaks)
Sealant on new gaskets is "over kill" 99 times out of 100. clean surfaces and new gasket is the way to go.
.
The timing issue, Larry (that guy obviously knows this 340 Buick factory timing setting) has made it clear "initial timing" 2,5* and full vacuum is the factory setting for that engine of yours. Still you got it pinging set up that way!!!
Considering this i must ask you this question: how did you check the 2,5* initial timing?
With a timing light at idle,(Larry, what rpm? 800?) and the vacuum adv.hose disconnected?(and plugged)
If this worked -67 with out ping,(and your running the oem distr) it must still work to day without ping, if timed properly.
with 2,5* initial and no vacuum, that engine must perform like crapp?
Lars

 

No, no, no sealant on the carb to pad gasket, that's why some pads need the Edelbrock plate, to make the carb pad on the manifold wide enough to seal the carb gasket to the carb base.

Plate to pad is sealed by gasket, carb to plate is sealed by a gasket that now has the full support of a larger pad area from the plate, no sticky goo needed.

 

Back on track?

67afone
Got the ping thing figured out yet?
I got a vision that you're running like 10-14* initial timing on a distributor set up to run 2,5*. This + full manifold vacuum advance gives to much total timing an you got the ping
Thats why i was asking how you set you timing....
My intention is not to be a pain in the b.... or something.
with 2,5* initial and no vacuum advance the low end must be bad.
Cant any one correct my numbers on what rpm the timing is supposed to be sett on that -67 340 engine? (if the problem isn't cured already)
Lars

 

Lars
I am only running 2.5 advanced timing with no vacuum advance connected. Yeah the low end sucks. But if Buick intended it to be that way how come when I set the timing at 2.5 advanced and then I hook up the vacuum hose it shoots it up so far that when I shut down the motor it diesels? Got any ideas?

 

Oooo "Diseses" (after run) that's another ball game, usually caused by:
1: (to) high idle speed
2: lean mixture
3: to hot spark plugs (wrong temp range)
4: glowing "sot"(deposits?) in the combustion chamber
(5: wrong timing)
or a combination of two or more of these things
Lets start with the idle speed, Adjust this with the vacuum advance CONNECTED, 700-800 rpm? (don't know the spec. for that engine)
Re check timing (with disconnected vacuum)
Btw. man or auto. trans?
Keep us posted, we will cure this!:TU:
Lars

 

I'd do all this:

The 2-1/2 degrees initial is just plain too low, I'd shoot for between 5 and 8 BTDC. Then, I'd restrict the vacuum advance degrees down to give me the correct total INITIAL/VACUUM DEGREES the engine ran stock, such as 2-1/2 + 15 = 17-1/2, now, say 8 initial, restrict the vacuum advance down to give 9-1/2 degrees, for 8 + 9-1/2 = 17-1/2.

Now, as the initial gets boosted, the mechanical needs to go the same route as the vacuum did, restrict the number of degrees available, as in 2-1/2 degrees and 30 would give 32-1/2 degres total mechanical, now, you'd stop the mechanical down to give 24-1/2 degrees, which would give 8 + 24-1/2 = 32-1/2.

You would also need to spring the mechanical for the correct rate of advance, as the stop would happen a lot sooner with the total degrees stopped down.

Stock specs are VERY conservative, and aftermarket curve kits of olden days did wonders for performance/driveability/economy. No reason the parameters can't still be sanely modified for the better.

I figure the weights/center/springs are somewhat worn, and would ned their sliding faces cleaned back up to not worn, and the springs changed to return the spring rate back to a workable situation. I get dists every day from all kinds of stock engines that simply will not spec to the factory settings, because the springs are sacked out. To gbet them back, I have to improvise other sporings, and that makes the setup work right again.

I'd figure the springs in this particular dist are somewhat sacked out, and the mechanical advance is just plain too quick.

 

the mening of Diesels?

With "diesels" do you mean run on a short time (and making a nasty noise at the same time) after you turn the key of, or do you get ping/detonations when accelerating ????
.
As for the low end boost you're missing, ther's no doth in my mind I-man just gave it "back" yo you!(at least the way how to)
I (and others, Larry70GS is obviously one of us, in fact he's one of them pointing me in the right direction) got pictures of how to restrict that vacuum movement and and how much in inches. Guess from who we got this?, the Ignitionman! As for restricting the mechanical advance. If you haven't done this before: it's a neat trick and involves some welding in sensitive distributor parts, precision is just the first name to it. To get it right your self (the first or even the second time) isn't easy.(believe me, been there did that) ........... what i am trying to say is: theres guys like Dave The Ignitionman doing this "all day long" think about it.....
No i'm not sucking up or trying to flatter or anything, no need to i just wrote my side of the story!
.
Larry, i thought he already had the 10-14* and non restricted vacuum (and got it pingig there bye) that was the vision, NOT wanthed him to try it.
.
Now again, 67AFONE what did you mean by dieseling? o No:
.
Ignitionman, is it ok with you for "us" to distribute them pix to other Buick:sters in need? o No:
Time here is 2400 Good nigth all!
Lars

 

Any pic I send is OK to be forwarded as needed, for whom ever needs it.

Getting the ignition timeing correct needs to be done first, as changes affect idle speeds and throttle opening positioning against the stop screw. As you all have surmised, the throttle plates are too far open to allow clean engine shutdown, and they have to be closed down a bit more to get the whole tihng to work right, but the timing situation MUST be addressed and rectified befroe the carb will ever be able to get dialed.