440 still idles with screws turned in

Moparnocar said:

Yes, new, around 6, bounces a bit

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I would regulate that down to 5 or less just to be safe. Edelbrock carbs will dribble fuel with not much more than 5#.

Geoff 2 said:

M/car,
Idle timing is a most understood topic, even amongst seasoned mechanics. The lower the idle vacuum, the more timing that is a needed at idle. Unless you are using a programmable ign 'box' [ & you don't need one ], the best way to give the engine the timing it WANTS is to use a dist with adjustable vac adv. Very cheap from Summit, $140. Set the Allen Key fully CW. YOU DO THE INTERNAL CENTRI CURVE LAST, NOT FIRST. Connect the VA unit to manifold vacuum { MVA} [ ported is USELESS ]. See link below. My engine idles @ 48* BTDC. Yes, 48, not a misprint.
D. Vizard has authored 30+ auto books, forgotten more than most will ever know.
Below is from a carb book, not an ign book. Hmm....
'The optimum idle advance is typically about 35-40* for a short cammed street engine & though not commonly realised as much as 50* for a street/strip engine'.

And from PHR magazine', Nov 04, while reviewing a new Crane dist:

' At idle....the amount of advance to most effectively utilize the air & fuel entering the engine can be as much as 50-55*. This is handled by the vac adv....By taking the time to hook up the VA to a manifold source you can get that big cam to idle as it were 20* less than it really is'.
Cannot stress enough how important this is to getting optimum carb performance & idle. Mopar missed the boat on MVA, GM used it & got it right.

More on MVA, scroll down to post #6.
www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html

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What octane fuel are you using? Race fuel isn't around here

Ok, manifold vs ported,

Mark

I like to run manifold vacuum advance when I can. I have my 67 GTX stock motor plumbed that way with 15 deg base timing and it idles and pulls strong off the line. It also helps keep the engine running cool even with the factory AC on hot days.

I also have a rather wild 66 427 Vette built with a lot of L-88 components, 12:1 pistons and a 256/[email protected], .579/.600 mech cam. I run 16 degrees base timing/36 total on it with manifold vacuum advance. Vacuum cans are available for GM cars that will function as low as the 8” idle vacuum the car generates. But - with 4:11 gears I was running all advance in including vacuum at a steady 50 mph cruise and it was kicking back constantly (like a slight continuous miss) due to firing so far ahead of TDC. I had to fabricate a limiter for the vacuum advance that limited it to 8 deg at the crank to clear the miss up. So depending on the engine too much of a good thing can be not so good sometimes.

AR,
Congrats on the smart decision. It is possible to have too much timing at cruise & get surging. But sometimes the surging is because of leanness, not timing. The use of MVA allowed the t/blades to closed more, which can cause leanness from the T slot. The fix is to enlarge the IFRs slightly.
Cooler running. Another benefit.

Master Gunner, Man v ported.
It is no contest. MVA does all the things that PVA...& more. So why would you bother with PVA? Did you know Ch used MVA?

Mcar,
You are still failing to grasp the use/benefit of MVA. Did you read the link I posted earlier, especially the last few lines??
My car uses 91 octane & using MVA does NOT require more octane.
MVA [ & PVA ] are load sensitive, not speed sensitive [ centri curve is speed sensitive ].
Here is an example & close to what I would use for your car: 16 init, 30 centri, 18 MVA. Car idles with 34*. Cruises with 34 + part/all of 30* centri. At WOT, MVA goes to zero so engine sees 36*.

I find it hard to believe only 6" of vac. Tried another gauge? Someone posted that there was a bad batch of these cams, maybe you got one. You need to some checking first before you start carb/ign tuning. I would check the cam position to see where the ICL is. If it looks right, I would advance it 4* to increase vac.

6bbl,
Post #36. Agree with much.........except drilling blades first & then playing with MVA. With MVA working, t/blades can be closed more. If you have already drilled holes & they needed to closed or reduced...pretty hard to put the metal back....
That is why I keep harping on about getting idle timing sorted before doing ANYTHING else [ as do experts like Vizard, ign timing in a carby book ].

Ok, sounds like a simple hose change to the manifold and he is good to go. Do you think every 1970-71 440-6 bbl, and Holley equipped 4bbl 440 should have their throttle plate holes plugged and a manifold vacuum line run also? So Holley is wrong, Chrysler is wrong, the vacuum gauge is wrong and Vizard is right? I seriously doubt it.

6bbl.
You can be as sarcastic as you like, but the above post is just showing ignorance. Every engine combo is different & whether or not the carb needs bypass air [ & throttle blades drilled ] will depend....
Ch added bypass air to TQs, but they did it by drilling the carb base. TQs used here on Fords had the blades drilled.
Ch also used MVA when they were forced to; they just didn't use it during the era when it would have benefitted most. From my 1973-78 MM, Ch section on emissions:" ...when coolant temp at idle reaches 225F, the bypass valve opens & applies MANIFOLD VACUUM directly to the dist.....This will increase engine idle speed & provides additional engine cooling".

The extra timing that MVA provides increases engine efficiency. That is why idle rpm increases: engine is making more HP. Because the engine is more efficient, it has less load & runs cooler. MVA is just ONE method of providing the extra timing.
In days gone by, before adj VA units, racers & hobbyists often locked their dists. If the engine reqd 36* @ WOT, dist was locked at 36. It cranked with 36* & idled with 36*....

DV is not the only person using or recommending MVA.
[1] Here is a Mopar story, MM mag Oct 15. They didn't used MVA, but they advanced idle timing from 15 to 26*, which simulates what MVA does. 416 stroker, 577 hp, so big cam".. a dramatic gain in low rpm throttle response was realized. If tweaked correctly, you'll see your idle vac creep up. And: "noticeably better off idle & low speed response & another inch of vac, The added initial timing raised rpm to 1500" [ was 1200 ].
[2] Super Chevy May 16: "Plugging your VA into a direct source will allow it to engage at idle, which is good for a number of reasons." And [ with MVA ] " the additional ign timing provided by the canister & full manifold vac source allowed the engine to more effectively burn the air/fuel mixture. It therefore produces more power [ even at idle ] & rpm rises a a result".
[3] PHR Aug 04. 480 HP SBC. "With VA hooked up....allowed a very smooth 650 rpm idle".
[4] PHR Dec 07. " the engine's minimum idle speed without the aid of VA was a lopey 900 rpm. With the VA it was 780 rpm with about half the lope".
[5] Super Chevy Nov 16 : "Carbureted engines with long duration cams will benefit the MOST from VA......This is counter to what you may have been taught in high school auto shop, but it is actually a reallllllllllly good idea".
[6] Circle Track Aug 04: " The only reason we need less low speed timing is so the engine will start easily".
[7] Ruggles QJ book: '"If we add additional timing at idle using a man vac source, engine vac increases & the idle quality improves."
[8] Edel carb handbook. Recommends MVA for low vac cams.
[9] Modern Engine Tuning by AG Bell: " At idle there isn't any vac with PVA but there is with MVA. This will provide an additional 16* advance to smooth out the idle & allow a leaner idle mixture".

Yes every engine is different, all are air pumps, this one does not pump well at idle. I hope you understand that at 6-8" of vacuum it is not sucking on the throttle blades as hard as one at 10-14"....and will need to get air from somewhere to idle off of the transition slots. X amount of cubic inches needs x amount of of air. That is why I said he needs 16-18 on the crank, 20 in the dizzy, and more air from somewhere. 2- 1/8" holes to start. He also has a small carb on it, so less gets around the blades, making them have to be open even more. The blades need to close to get his mixture screws to work. The engine needs the same amount of air no matter where the timing is. Once he gets the idle rpm where he wants it, with mixture screws 1-2 turns out, 16 on the crank, throttle blades closed, then he can play with the vacuum advance to try to make it even better. Vacuum advance will not overcome the basic law of physics that it need x amount of air per cubic inch. Offer him a better solution before calling me ignorant on the subject, as I am still learning too.

For the fun of it check out Unity Motorsports Garage on you tube " The ultimate vacuum advance video part 1 & 2. Andy pals around with David Vizard.

Geof, If you are going this method you better map all of your ignition, and vacuum signals. You need a good graph of what your engine vacuum is at all states, mechanical timing, and vacuum timing. How fast is mechanical timing, where does vacuum start adding timing and how does it graph, but more importantly if you use MVA is how does it come off signal. We try to help folks but we really don't know sufficient data, and he doesn't know if he has problem component. Obviously some folks know about this cam, and that is an issue. But we need to know the distributor timing curve and max mechanical. How does the vacuum can curve.
The other point is, once off idle the ported vacuum comes in and matches MVA until vacuum falls off. My understanding has been that using MVA is all about a method to handle the cam and still allow start ability. Regardless, 6-8" is not good for a edelbrock signal wise. I would think it would need major mods to work that way.

Geoff, if you did a search you would find that the manifold vs ported vacuum advance subject has been pretty much beaten to death a number of times. Chrysler has used ported advance since the 50's, but it's up to you what you want to do for your application.

Mark

His carb will work, but will need mods. If he determines that he has no vacuum leak, and I doubt he does, gets 16 degrees timing on the crank and 20 in the dizzy, the balancer may be off, find TDC mechanically, he can mod the carb. Pull the carb and see where the front throttle plates are in relation to the transition slots. If they are exposed start drilling the plates, if you are afraid start with a .090 drill. It is also wise to go to a hardware store with a micrometer and buy bits every .005 larger and drill them one size up at a time. Whatever you do don't start at .125 then say wow that helped so I will go to 9/32, or .180, that is way bigger, .005 at a time once you hit .125. One other warning as you get the blades to close it may want to die due to lack of fuel, as you are no longer drawing on the transition slots. You fix this by drilling the idle feeds .001 at a time until it runs with blades closed, and the mixture screws 1-2 turns out. You might be able to fix the lean idle with more timing from the vacuum can at this point also, with 8" or less vacuum it may be a challenge to get 12 degrees but you can try. Your choice on that. When you loosen the Allen screw in the vacuum pod it will respond at about 8", the problem is at highway cruise, when vacuum is high you will get a high speed miss...run it up to 3000 rpm and listen for a miss, and check the timing big blocks can usually handle 50 degrees total at light load. You may need to limit the travel of the vacuum advance with a piece of wire if it high speed misses. Most hex head vacuum cans are adjustable. You will be removing the carb a lot to do this right, I like a felpro gasket that I grease both sides of so I get a good seal without cranking the carb down hard every time until I get close. Good luck

4406bbl.

I apologise for my comment in post #50.

All I am trying to do is to help the OP with his problem & using MVA is one method of doing it. It is the simplest & most reliable.
Interestingly, Nick of Nicks Garage fame & Mopar fan, has started using MVA recently, & most recent was a 440; he noted a 'smooth idle' at 950 rpm.

I am well aware of leakage around the t/blades, & that it contributes to the overall air reqd at idle. Idle air is also drawn through the PCV, idle air bleeds & t/shafts. The totality of the flow is what counts & the engine doesn't know....or care...where the air comes [ could be an air leak, gasket etc ] as long as it gets it.
You are still not getting the message about the tuning sequence. You do idle timing FIRST.
I have provided you with plenty of examples. The last thing you do is bypass air, if needed.
You talk about the basic laws of physics. Relating to idle, there are two basic laws here: [1] the engine will require a certain amount of timing for best idle quality, vacuum & minimal fuel consumption [2] The volume of air inducted never changes at that rpm, but it's density does. At low rpms the air is 'throttled', less dense. More distance between molecules, hence the need for ign advance so that the mixture can burn as completely as it can. When cam duration increases, you get more exh dilution, which also slows the burn rate, & more timing needed. More timing at idle produces more vacuum & that changes the density of the mixture [ not the volume, fixed for the rpm ] & therefore t/blade position.

DS,
I mentioned earlier in this thread that above idle, MVA & PVA act the same. Agree with many of your comments.
As far as ign timing graphs go: great if the engine is a stock rebuild. That goes out the window when you start changing components.
The only proper way to map an ign curve is put the engine on a dyno & do graduated pulls at say, 200 rpm intervals. Adjust timing at each interval for max HP & note. There is your curve. This of course is beyond most people so they just work on WOT timing & take an educated guess at idle to WOT.
6-8" of vac is not a good starting point for any carb, Edel, Carter or Holley. But vac will increase with the timing increase.
Can you do me a favour? Takes 5 min. Do you have performance cars with running engines & currently using 10-18* of initial timing? If so, disconnect & plug VA if used. Warm up engine, at idle, loosen dist clamp & slowly turn the dist to advance the timing to highest rpm. Rpm will increase & idle will get smoother. Check what the timing is [ optional ]. Let us know the result.

6bbl,
Post #55. A lot of good advice. Cruise timing can & often is more 50* at light cruise. Could be 60 or slightly more. Big cam, low compression wants more. Poor combustion chamber design [ needs a lot of timing at WOT ] needs more. Often surging at cruise is from leanness, not excessive timing. Enlarging the IFR will usually cure the problem. To see if it is leanness & the carb has a choke, close the choke slightly to see if it fixes the problem.

You missed my point. You're diagnosing and you know nothing about the patient. Ignition system, amount of mech advance total, and how quick it is in, vacuum can max adv, etc... I have seen folks dial in 20 plus initial not realizing that the distributor cam of a 70ish mopar could add 30 to 34 degrees timing. Plus they removed the heavy spring and all in at 1500rpm. At wot they have 50 plus degree. Vacuum cans can add 26deg or more timing.

This is all about idle timing, ported is nothing more than an automatic switch turning on the vacuum can as throttle blade opens. Each carb has a point where that occurs. When the port is uncovered and exposed to manifold vacuum. For Chrysler in stock form, as you accelerate mechanical advances and vacuum may starts to add too, unless a WOT acceleration. So both maybe adding.

In your case to compensate for a mismatch in components CAM/Carb. You Add via vacuum initially, so what happens when you accelerate. Again you have mechanical add, and maybe a little vacuum or maybe it starts to retard. That graph is completely different looking than a stock set up. So is it as good? You say yes, others say no.

Also, so why does vacuum increase when you advance timing?

Just as a comment on 6bbl instructions, which I like, you don't want fully closed throttle blades do you? I think you want a portion of the transition slot uncovered for proper mixture volume. Once your satisfied you might need to adjust pump shot too if any stumble off idle.

Dragon Slayer said:

You missed my point. You're diagnosing and you know nothing about the patient. Ignition system, amount of mech advance total, and how quick it is in, vacuum can max adv, etc... I have seen folks dial in 20 plus initial not realizing that the distributor cam of a 70ish mopar could add 30 to 34 degrees timing. Plus they removed the heavy spring and all in at 1500rpm. At wot they have 50 plus degree. Vacuum cans can add 26deg or more timing.

This is all about idle timing, ported is nothing more than an automatic switch turning on the vacuum can as throttle blade opens. Each carb has a point where that occurs. When the port is uncovered and exposed to manifold vacuum. For Chrysler in stock form, as you accelerate mechanical advances and vacuum may starts to add too, unless a WOT acceleration. So both maybe adding.

In your case to compensate for a mismatch in components CAM/Carb. You Add via vacuum initially, so what happens when you accelerate. Again you have mechanical add, and maybe a little vacuum or maybe it starts to retard. That graph is completely different looking than a stock set up. So is it as good? You say yes, others say no.

Also, so why does vacuum increase when you advance timing?

Just as a comment on 6bbl instructions, which I like, you don't want fully closed throttle blades do you? I think you want a portion of the transition slot uncovered for proper mixture volume. Once your satisfied you might need to adjust pump shot too if any stumble off idle.

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Agreed. Post #9 was my condensed version. Nicely explained, Dragon.