This is incorrect, ported vacuum has been around just as long as vacuum advance, at least since the 1930s. If you dig in the old manuals, the reason it was used was to allow for a steady idle. No surprise there. Some manufacturers did use constant or manifold vacuum.

The timing instructions do specify disconnecting and plugging the vacuum advance port, this is probably just a "belt and suspenders" approach because when the idle RPM is set above factory spec (common) the advance of course starts to tip in and bugger the results at the damper, but at factory idle there will be no advance even when connected.

There will be a lot of advance at idle if manifold vacuum is used, but the engine isn't under any load, and as soon as it is, the vacuum advance will go away. Most engines will idle happily from 15 to 30 degrees advance. The best advice is to the OP is try it and see what you think, limiting the total mechanical (initial crank + distributor) to around 34 or 36 degrees by 3000 RPM.

 

The OP has a Carter....no power valve in these carbs.

Unfortunately, that "blow out protection" dealie - a little spring and ball in the base, implemented by Holley since '92(?)...or '96 - doesn't always work. I have a 4160 model, #1850 bought in '010. A small fart happened one day while dumping the clutch.....blew out the P/V. I took it apart, drilled out that POS spring and ball, and have been shi**ing in tall cotton with it ever since.

Tedster9: All I remember using, back in the day, is manifold vacuum. Wasn't even concerned with looking or using ported, if it was even there. Mebbe that's why I never found it.

That was when nice, pink, leaded high test gas was around a quarter a gallon. I hooked up my truck to manifold vacuum for a spell. Went back to ported...not a bit of difference. I don't have a huge bumpstick in 'er and I like the sound of the cam. Also I get a sh$t eatin' grin when some waana-be motorheads tell me I need a tune up.

JKessler00: If the carb is clean, setting the mixture with a vacuum gauge would show different readings. Try pulling out the mixture screws and blowing a little air in the holes. Try adjusting again.

That "pop" you heard when punching it at idle could be a lean carb backfire. Clean out the mixture holes and try again. Other than that, mebbe the main circuits are dirty.

Not to worry about that article that stated a "good pop through the carb......etc" as the article was about Holleys and not Carter/Edelbrocks. You're good to go.

 

The idle mixture needles can make a big difference on how the engine runs, especially cleaning up off idle bog. Using an O2 sensor I'm told as little as an 1/8th or 1/4 turn can equal a full point in the A/F ratio, but it won't change RPM or anything like that, in other words you'd never know otherwise. I like to lean it out slightly maybe 50 RPM drop and bring the idle speed back up "best lean drop". If you have to pass smog this is an important step.

 

If you saw zero vacuum then most likely you were using the ported vacuum nipple on the carb. If you saw no change the idle rpm might be set too high. You need to plug the gauge into full manifold vacuum when adjusting the idle mixture screws. Usually the port beside or in the manifold. Adjust the mixture screws for highest vacuum. Start on 1 side at a time by screwing each side in until the rpm drops then adjust back out until up to peak rpm and just enough to achieve peak rpm. Then adjust idle speed down to desired setting and recheck if you want.

If you do this and still find you have a hesistation then you need to play with the accelerator pump circuit.

 

I am definitely using ported vacuum for the advance and I was also using manifold vacuum to check idle mixture. There is a port right on top of the Performer manifold. It was a pretty steady 19", regardless of how I turned the screw, which really surprised me. I'll pull the screws tonight and see if they're dirty. I do not have a smog test to worry about.
The accelerator pump lever was in the second hole from the bottom before I rebuilt the motor. The Carter manual says to use the lower hole so I did semi-recently move it.

 

I popped the hood this afternoon and noticed the cap was missing on the manifold vacuum port. I put another one on and the backfire seemed to disappear. I revved it a few more times and the backfire came back. I looked under the hood and I had blown the cap off again...doh! This time I added a clamp and I think I'm in decent shape.

The idle screws were perfectly clean. I went around the block and I didn't have pinging but throttle response sucked. I'm thinking I'm too rich at 1 1/2 turns on the idle screws. I backed out to two turns but didn't have a chance to drive it again because I had to take my daughter to an appointment.

 

It wasn't the idle screws I was talking about....it was the holes in the carb where the screws set in.

The 1 1/2 turns out on the mixture screws isn't a hard and fast rule...nor is it the epitome of a correct mixture setting. That's just a guide. Every engine will be different.

Backing the screws out - CCW - will make the mixture more "rich." Turning them in - CW - will "lean out" the mixture.

I'm still surprised at no change in "Hg when you adjust the mixture with the vacuum gauge hooked to manifold vacuum. That's curious.

 

The holes were nice and clean as well; I should have specified. I guess I had it backwards with the mixture. It sounds like I need to turn them in a little more and see if throttle response improves.

 

Yessuh, let us know what happens...

 

I'm bringing this back to life as I continue to battle with it. I didn't reread my own thread to see what I last relayed to you all but I found a bent metering rod in the shape of an "L" when I tore the carb apart. Power still lacks and I still have the pop in the carb when revving from idle. I was running .095 jets in my primaries and .098's in secondaries. I've trialed all different sizes. I'm currently running .101's and .107's and while I believe I've made progress, I still have a little bit of a pop when mashing it from idle. Throttle response sucks. I even moved from a 30 to a 24 nozzle on the accelerator pump.
I'm using the middle hole on the rod, which appears to give me the 15/32" spec from the manual. One the of kits I purchased has different springs for the accelerator pump as well. Anyone messed with these or know the effects of changing to stiffer/lighter springs?
I'm going to see how much mechanical advance I'm getting from this distributor. I'm running 18* base with no pinging. If I jump to about 20* (being that I'm much more rich now with the new jets), I start pinging.

 

I have never messed with an edlebrock carb before but this article explains how it works and what you need to do to fine tune it.


Tuning an Edelbrock Carburetor - FordMuscle

 

Yoh JK,

With regard to getting a zero vacuum reading, read post 57 and then post 64. Enough said !

When you get the starting issue sorted and can run the engine, buy a decent vacuum gauge (umm, not a brake bleeder !!??) and connect it directly to the intake manifold when the engine is off and is at operating temp. (You might have to buy an adapter to fit the gauge.)

Start the engine. What is the reading, and how does the needle behave ?

Put things back the way they were, and then with a timing light, measure the timing. Is it 13* at 580 rpm ?

Then disconnect the ported vacuum advance pipe and connect it to full manifold, and plug the ported.

Bring the idle back down to 580 rpm, or whatever it was, (this is to compare apples with apples) and read the timing. What is the timing ? ( +/- 33* ?)

Put things back the way they were.

Contrary to post 51, 33* will be fine, but we'll get back to that.

And lastly, for now, did you fit the cam with the 0 to 0 lined up on the sprockets, and are you 100% sure of that ?

 

I have since purchased a better vacuum gauge than a bleeder

The timing gears are definitely 0 to 0.

I have plenty of tinkering and trial and error yet but since I now have a different engine with similar issues, I'm starting to think the carb is the common denominator.

 

Haha, funny you should mention the carb.

I hinted at it in the other thread but decided to leave comments about it until everything else was addressed.

LOL @ the bleeder, and glad to hear the cam timing is 'straight up'.

The accurate vacuum readings will be an excellent reliable starting point for diagnosis when you're ready.

Do you understand now why you were able to get a zero vacuum reading ?

Laterz,

 

Originally Posted by JKessler00
I appreciate all of the input. I'm still messing around with this. One question that no one has answered is what timing should I have at idle with vacuum advance? It was mentioned that both 39 and 33 were too high.


At idle there isn't any load on the engine. Manifold connection pulls in lots of advance at idle, it's true, this is NO problem, it will run cooler.

At wide open throttle the manifold vacuum goes practically to zero, so the ignition advance at that point has reverted to the mechanical limits. Once the load levels off the manifold vacuum returns, while at the same time the RPM drops off. Two independent advance mechanisms that work hand in hand, though when one is advancing the other is generally retarding. At steady level cruise conditions in high gear the load is low again, and manifold vacuum high. The OEM curves usually have around 50° BTDC under these specific conditions. It only takes a small amount of horsepower to cruise on level ground. The fuel mixture is very lean, so lots of advance is needed to light the fire early.

The engine will run cooler at idle with a manifold connection. In the smog era they were big on reducing NOX levels, and ignition timing at idle was reduced because of this. The ported or "timed" source was used. They did have sensors or solenoids to default to manifold vacuum when the engine overheated, to try and keep it from turning to scrap. Any street driven engine needs vacuum advance. It will run cooler at cruise and at idle. Better mileage, better all around driveability. The problem with a manifold connection at idle is usually difficulty achieving a steady idle.