Tuning issue on a 440

carfreak6970

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Hello,

I am not to sure if this is a fuel issue, or a timing issue so I figured I would post in this section:

I am having a tuning issue on a 70 polara and I think the issue is carb related. My guess is either the springs for the rods are too light or I have a vacuum leak. Here are the details:


The car is a 70 polara convertible with a 440, 727, and 3.23 suregrip. The engine was rebuilt 15,000-20,000 miles ago and never really had a problem with it. It has a stock iron 4 barrel intake and stock iron heads. It was rebuilt to either 69-70 magnum status. It currently has a Carter AVS on it (I believe it is the 4640S) that I rebuilt but got from Chryslers at Carlisle last summer.


So the story goes is that the car initially had a 71 AVS (4966S) which is a 440 carb but it has smaller primaries. It ran good, no issue. The initial was set at 12 BTC. I decided to rebuild it and noticed that the secondary and primary jets were swapped. So I put the jets back where they should and put the carb back together. The car didn’t feel as spunky as before and there was a slight ping under heavy load. The initial was still at 12 BTC. I figured it was due to the carb being a little too small, so I searched out a 440 AVS with the 1-11/16 primaries. I found the 4640S that is currently on it last year and recently rebuilt it and installed it.

When I took it out for a drive I noticed the car had a noticeable amount of pick up and go and I was really happy with it, however it pinged now under any type of load. Load being pulling away from a stop sign at night. I could only “gingerly” accelerate to keep it from pinging. This is with it still at 12 BTC. So I figured I would decrease the initial and see what happens.

Well I was able to drop it to 8 BTC and took it out for a ride last night and pleased to report that there was no more ping. However, the engine temperature did not like the change. The temp gauge fluctuated like it never did before and after parking it for a couple minutes there was a puddle of coolant sitting under the over flow tube that was about 6 inches in diameter. Again, never did that before.

From what I am reading mopar big blocks can like 12-16 BTC with around 30-36 total timing. So it would make sense that when I back off the timing the temperature raises a bit (at least that is what I gather from searching mopar forums). But with me putting the timing in that 12-16 range I get pinging, which from what I read is too much timing. OR, a lean mixture.

Now I was able to verify that the 4640S carb did have the correct size jets and rods, but I had no way of checking the springs. So here is what I believe could be the top issues:


1. The amount of timing the distributor is putting in is in access of 20 degrees. Which I doubt. I don’t know what timing it is putting in and when, but considering this excessive pinging was not an issue with the other carb at this timing I am going to say it probably isn’t the distributor. But, I can easily check that, I have a distributor machine I can put this on to verify.

2. The springs in the carb are too weak preventing the rods from allowing more fuel into the mixture. I know with Holleys you can get power valves based on vacuum ratings and you can easily have a vacuum gauge to read where vacuum is at in certain situations and change your selection based on that. But I don’t know if the carter AVS has that ability with the springs. I could go through my spring stash to see if I have stronger springs that would allow more fuel into the mixture at a high vacuum rating. Only way to verify spring strength is by feel correct? Or was it based on height of the spring?

3. Lastly, there is some vacuum leak that is allowing air to come in at a different point and bypass the venturi which would not bring in the metered amount of fuel. I feel like this is probably my best bet. I reused the carb spacer and gasket. I have reused this carb spacer and gasket before and never had an issue, but that is not to say it is not an issue now. Or it could be that somewhere in the casting of the carb it is either warped or cracked. The reason I feel this is the best bet is that when trying to set initial timing and idle speed the rpm varies by +/- 50 rpm and the timing mark with the light does fluctuate +/- 3 degrees, which it did not do before this most recent carb swap.


So I can see if I have strong springs to allow more fuel in sooner. Is there a way I can check a vacuum leak at the carb? And I can limit the amount of timing the distributor puts in with an FBO limiter plate. Am I on the right track? Am I missing something? Is there anything else for me to check? I was going to get a small tach that I can have in the car so I can document when the pinging comes in to see if it is based on RPM, and where the pinging stops to help change the curve if need be.


Thank you
 

66Valiant528

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I've never had a BB that didn't like more fuel! Are you sure it's not a lean ping? Try adding more pump shot if you can.
 

roccodart440

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Unplug the vacum advance. Set the timing to 36 total. Use premium fuel (91+) and test drive it. LEt us know what happens.

NOte: to set total timing you have to rev it until the light line stops moving, which can be 3,500+
 

Lefty71

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Is the distributor bone stock??? If so, look for a black box with a wire leading to it on the side of the distributor, in addition to the vacuum advance can. Let me know if it's there....
 

carfreak6970

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Do you have a gauge on your FP regulator?

I do not. This is just a mechanical fuel pump with no regulator. Essentially a stock system

Unplug the vacum advance. Set the timing to 36 total. Use premium fuel (91+) and test drive it. LEt us know what happens.

NOte: to set total timing you have to rev it until the light line stops moving, which can be 3,500+

Thank you for that information. Given that this is a holiday weekend I wont have time to do this. But I will give it a go and report back.

Is the distributor bone stock??? If so, look for a black box with a wire leading to it on the side of the distributor, in addition to the vacuum advance can. Let me know if it's there....

To my understanding we have never modified the distributor. So yes it is stock. There is no black box with a wire leading to it on the side of the distributor

To aid in tuning would it be a good idea to get a simple AFR gauge and attach it to the tailpipe with something like this?

https://www.amazon.com/dp/B000CO9MF8/?tag=fabo03-20

Some places say the readings shouldnt be that different on a car without a cat when measured from the tail pipe outlet.
 

Bewy

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Congrats on using an EXCELLENT carb.

Comments/suggestions:
- Edel AFB/AVS springs will work. Use this method to test for best springs. Loosen met rod piston covers, twist slightly, retighten so that you can see the piston, but piston is still captured. Go from softest to stiffest spring. Warm up engine, idling, in gear; pistons need to stat DOWN & not move. Change to stiffer spring & re-test. If piston moves, spring is too stiff. You want the stiffest spring that just stops the pistons moving.
- if ^this does not help, try a larger pri jet or a met rod with thinner power step; you can file them.
- you have gone to 1/4" larger primary barrels/venturiis. That reduces signal strength AND atomisation quality. It can also change the a/f distribution in the intake. Many of these AVS carbs had snivs riveted to the pri booster to re-direct air; a real band aid fix. It might only be one or two cyls running lean, no way for the home mechanic to really tell.
- do everything you can to get the engine running cooler; heat is the enemy of detonation.
- the springs for the centri weights in the dist may have stretched, allowing timing o come in too soon. You could try heavier spring, remove metal from the weights.
- remove the carb & check the gasket against the base for leakage. I doubt you have an air leak. While removed, check how much T slot is showing below the pri blades; should be 0.040" or less. More than this will require bypass air & enlarging the IFR.
- how much throttle opening is being used when you get the pinging?
- float level correct?
 

carfreak6970

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Congrats on using an EXCELLENT carb.

Comments/suggestions:
- Edel AFB/AVS springs will work. Use this method to test for best springs. Loosen met rod piston covers, twist slightly, retighten so that you can see the piston, but piston is still captured. Go from softest to stiffest spring. Warm up engine, idling, in gear; pistons need to stat DOWN & not move. Change to stiffer spring & re-test. If piston moves, spring is too stiff. You want the stiffest spring that just stops the pistons moving.
- if ^this does not help, try a larger pri jet or a met rod with thinner power step; you can file them.
- you have gone to 1/4" larger primary barrels/venturiis. That reduces signal strength AND atomisation quality. It can also change the a/f distribution in the intake. Many of these AVS carbs had snivs riveted to the pri booster to re-direct air; a real band aid fix. It might only be one or two cyls running lean, no way for the home mechanic to really tell.
- do everything you can to get the engine running cooler; heat is the enemy of detonation.
- the springs for the centri weights in the dist may have stretched, allowing timing o come in too soon. You could try heavier spring, remove metal from the weights.
- remove the carb & check the gasket against the base for leakage. I doubt you have an air leak. While removed, check how much T slot is showing below the pri blades; should be 0.040" or less. More than this will require bypass air & enlarging the IFR.
- how much throttle opening is being used when you get the pinging?
- float level correct?

I was able to put the distributor on my Sun machine this morning and this is what I found:
- 5 deg at 800 (1600 engine rpm)
- 8 deg at 1000 ( 2000 engine rpm)
- 10 deg at 2200 (4400 engine rpm)

Vacuum advance is as follows:
5 deg at 13 inHg
10 deg at 16 inHg

Which is close to the 70 HP curve and such. So my distributor is putting in a max of 20 degs at 4400 engine rpm

I understand your testing method for the springs. However, would the rods still be down at idle? since fuel would only be going through the idle circuit and not the main circuit?

But thank you for that simple method of tuning! I posted the same question on Cbodies and someone answered with how to tune the Vac can and that jets should be 1.05 times larger for E10 fuels. So this is all good stuff! thank you all!
 

roccodart440

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Pull the vacum advance and see what it does.

10 degrees of advance at 4400 should run fine even if you set the base to 24 degrees or more, IF the vacuum advance is disconnected.

I think your VA is coming in too much, too soon or yielding too much total timing.
 

Bewy

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Carfreak.
Yes the rods MUST be down at idle. In a nutshell, you want the strongest springs that will keep the rods down at idle.
I think you need to change the centri curve. You are getting half of the centri timing in by 1600. If you can reduce that with a heavier spring, I am sure it would help.

Comment about the carb. I hope yours has conventional idle mixture screws [ two ] at the carb base. Some AVS carbs do not have these, or have a single air screw up near the air horn.
Adjustable idle is important because you cruise on the idle cct at lower speeds. Lean idle [ because it cannot be adjusted ] makes the engine run hotter. Then, when you take off the engine is already 'hot' & you get pinging.
24* initial would definitely not be 'fine' with a 20* centri curve.
 

Mattax

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When I took it out for a drive I noticed the car had a noticeable amount of pick up and go and I was really happy with it, however it pinged now under any type of load. Load being pulling away from a stop sign at night. I could only “gingerly” accelerate to keep it from pinging. This is with it still at 12 BTC. So I figured I would decrease the initial and see what happens.

Well I was able to drop it to 8 BTC and took it out for a ride last night and pleased to report that there was no more ping. However, the engine temperature did not like the change. The temp gauge fluctuated like it never did before and after parking it for a couple minutes there was a puddle of coolant sitting under the over flow tube that was about 6 inches in diameter. Again, never did that before.

From what I am reading mopar big blocks can like 12-16 BTC with around 30-36 total timing. So it would make sense that when I back off the timing the temperature raises a bit (at least that is what I gather from searching mopar forums). But with me putting the timing in that 12-16 range I get pinging, which from what I read is too much timing. OR, a lean mixture.


Since you have Sun machine, plot out your distributor's advance curve and then the timing curve using a few initial.
Compare that to the advance and the initial for a factory '70 440.
Note the 2 bbl and 4 bbl often have difference advance curves....
Keep in mind that 1970 distributor will be set up as part of the CAS of that year. By 1970 CAS was purposely putting more heat into the cylinder walls and exhaust - especially at idle. If you want to go pre-CAP/CAS and use a 12-14* initial, then off-idle advance curve needs to be brought in line with a non-CAS '66 or '67 distributor. See discussion here
Base timing. Really ?
 

roccodart440

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There should be no question on total timing. After locking the dizzy, you rev and check total advance. i'd recomend marking it on your balencer. Makes setting timing easier if you pull the dizzy for any reason.
 

carfreak6970

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How did you determine that the jets were installed backwards?
You know that on that carb,
the bigger ones go under the metering rods..... right?

Thank you for that information. When I said "bigger" I meant the taller jets. Furthermore, I have a pin gauge set and measured them out and placed them in their respective areas according to the FSM. And the carb I did that jet swap on is no longer on the car.

Unplug the vacum advance. Set the timing to 36 total. Use premium fuel (91+) and test drive it. LEt us know what happens.

NOte: to set total timing you have to rev it until the light line stops moving, which can be 3,500+

Pull the vacum advance and see what it does.

10 degrees of advance at 4400 should run fine even if you set the base to 24 degrees or more, IF the vacuum advance is disconnected.

I think your VA is coming in too much, too soon or yielding too much total timing.

For testing purposes I did just like you described. I set the initial to 16 BTC with an idle rpm of 750 with 18.5 inHg going from the port on the intake that the power brakes feeds from. I set it at 16 since I have determined with my Sun machine that the distributor puts in 20 degrees of mechanical advance. I disconnected the vacuum pod and plugged that port on the carb.

Off idle is good. it is hard to tell if the off idle was better than the 12 BTC setting, but was better than what it was just at. Under moderate acceleration I did not hear pinging, but under spirited acceleration there was. I did not hear any pinging at steady state cruise at various speeds (20, 30, 40, 50). I did a couple WOT in first and second and I did hear pinging through out the rpm range during that test.


As mentioned above I verified the carb is set up to the FSM (jets and rods) with the exception of the rod springs , since the book does not specify spring rate. A member on cbodiesonly said that when jetting the car to the FSM one should account for the E10 fuels by 1.05 times. Is this sound thinking?

I did not do the rod spring test at idle yet, I wanted to get some springs before I do that. I should have them ordered today.

I am trying not to just change everything at once. I am trying to change one thing at a time to see how it reacts. Ideas on next steps?
 

roccodart440

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Assuming you checked total at RPM, you had 16/36.

If it pinged at this setting, the next thing to do is make sure you are running premium fuel (91-93) and pull the timing back to 14/34, re-test
 

carfreak6970

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Assuming you checked total at RPM, you had 16/36.

If it pinged at this setting, the next thing to do is make sure you are running premium fuel (91-93) and pull the timing back to 14/34, re-test

Okay, I am assuming that I continue to go down until I find a max timing until I dont hear pinging? At which point I hook up the V can? When would I start with the jetting, rods and springs of the carb?
 

MOPAROFFICIAL

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Already been said by Rocco. Put 91 in it and disconnect the vac canister.
Once you verify the ping is gone or not..then address/reconnect the vac canister and see what it does .
It's a 1970 440..it still has some squeeze.
 
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carfreak6970

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Okay, I ran another test last night. I was able to back the timing down too 14/34, still had the idle set at 750, but was not able to get a vacuum reading since my gauge was packed up sitting at work. Vac Canister was still disconnected and plugged on the carb

It ran really well! there was good pick up and pinging was almost non existent. The tank was filled with 93 ($84...). Under WOT there was a slight ping until the RPM's got a little higher. Under heavy load acceleration (going up one of those hills around here) there was some pinging present but not like what it was. I will try to do 12/32 soon.

Would I only start messing with the carb after I connect the V Can? I already know with the V can attached at the 12/32 setting there is pinging. Would I adjust the vacuum advance down or would I start with the rod springs/rods/jets?
 

roccodart440

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70 polara with 3.23 gears.... Heavy with tall gears under load isn't going to be as octane friendly.

Try the 12/32. Sounds like you are really close to a working tune.
 

carfreak6970

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Okay, finally got a chance to do this test:

70 polara with 3.23 gears.... Heavy with tall gears under load isn't going to be as octane friendly.

Try the 12/32. Sounds like you are really close to a working tune.

Car loved it with not pinging at all! next step? plug in the vacuum advance and slowly start pulling the vacuum advance down?
 
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