Carter AVS Part 2 on the car tuning

[HS 69 Charger]

Per my previous thread the Carter AVS is all cleaned, reassembled and bench aligned. Now its back on the car. Operation is much better but I think that is more how I am setting it up than the actual rebuild (or both). One thing I found wrong, was that I think I previously (a while back) accidentally set the Timing without disconnecting the Distributor vacuum advance. After I correctly set this, all the adjustments seem to work better as I walked through the idle mixture screws and Idle set point. I did also throw on new spark plugs to do everything with a solid baseline. So now with the timing setup, the adjustments seemed to go much better.
One question, when setting up the idle mixture screws I ended up doing this with the Distributor Vacuum advance disconnected. When doing it this way, I found it was more consistent and I ended up being able to adjust the Idle Mixture more lean. With the Timing done correctly and the idle mixture screws adjusted the Idle was more stable and the general ride and acceleration was much better too.
Previously, my idle was terrible and as the car got very warmed up it would stumble down below 600rpm and then eventually just die. I got so I kept a little gas on at the stoplight. This all kept getting worse over time.
Now, it still has a bit of idle stumbling idle but is much more stable and doesn't die out. Idle setting in Neutral is about 700 to 750 with in gear about 650. In park about 800.
Acceleration at any speed is fine and from idle is ok but sometimes just a bit of hesitation. Previously it just sat there until it decided to take off "later". While the accelerator pump was worn out I believe it was more than just that item.
Lastly, the Vacuum during the above setup was only about 10 to 11 at idle. The cam was replaced long long ago but should have been only a mild street upgrade from stock. I don't know what to expect for a 383 with the Carter AVS carburetor.
As a side note, prior to this project I was working on my dash and in that process, I fixed the vacuum headlight switch. The vacuum headlights have never worked better and are extremely strong in both open and closed position. I only mention this because I have seen people ask about vacuum leaks and often with the headlight system so I wanted to rule this out. Plus symptoms I've seen were both before and after this work. But I do know this is very solid now. It was a win.
I plan to run for awhile and try to take note of any anomalies to provide any further insight.
PLUS, I located a source for 91 octane no ethanol fuel. I am going to start fueling up with this and might have to readjust mixture settings as needed.
In case you missed my other post the setup is:
1969 Charger 383 Vin H with Carter AVS 4638S. The car is virtually stock matching the Build Code sheet including 3.23 gears.
It was converted to Electronic Ignition Mopar kit P3690427 in 1988 with ECU P4120505 (orange), and Ballast P5206436. Coil is original.

 

[oldbee]

Idle speed in neutral/park should be the same. Sticking advance weights? Maybe slight vacuum leak? Just spitballing here.

 

[Some Car Guy]

You might still have an issue with the accelerator pump. Might not fit the bore just right. I believe there are two versions you can check for sizing. Also the pump shot can be changed among the three holes.

You might have an old mopar cam. Those were common upgrades and have low vacuum. Even a 383 hp would have more vacuum than what you have.

The other guy has some good thoughts too.

 

[Don Frelier]

Idle speed in neutral/park should be the same. Sticking advance weights? Maybe slight vacuum leak? Just spitballing here.

The pump runs in neutral and not in park so they could be slightly different.

 

[turbine68rt]

With a Carter AVS there is only one source for distributor advance, which is ported. You shouldn't be pulling any vacuum at idle anyway using that source. The 727 pump is spinning any time the engine is rotating since the converter hub engages the pump lugs. Line pressure is lower in park (0-30psi) than in neutral (57psi).

 

[HS 69 Charger]

After a bit of digging, I found the info on the Crane Cam installed in my car back in 1990. Now, as I hold my breath, you can tell me what comments you have on the CAM and if it is the influence of the lower vacuum I see at idle. I know nothing about cam specifications.

I should also ask what is the proper pickup point for my vacuum measurement. The carburetor has 2 lines. One for the Choke Pull off and one for the Distributor Advance.
And the back of the manifold has a large fitting for the headlight doors (line to canister) and a small port take off that runs the inside ventilation doors on the Heating/cooling ducts.

Thanks for additional information.
Martin

 

[Geoff 2]

OK.
[1] Use the small port at carb rear for vac gauge readings
[2] If you are/were getting vac readings at idle from the ported vac source on the front of the carb, it means the pri t/blades are open too far, exposing that port to idle vacuum. That does not surprise me that cam in a 383...& it is no good. It is also causing your off idle flat spot because the position of the t/slot relative to the t/blade is critical to off idle performance. The pri blades are open too far.
[3] T/slot. You need to remove the carb & turn it upside down. See the holes in the pri bores for the mixture screws? Just above each hole is a slot. That is the T/slot. I am expecting that with the blades closed against the throttle stop screw, there is more than 0.060" of slot showing below the blades, which is too much. 0.020-0.040" is ideal & 020 is better. The problem is.....if you back of the speed screw to reduce the t slot gap, the engine will stall. The problem is caused by the cam having low vacuum at idle.
[4] To fix this problem [ later ] you will need to check that the t/slot position is correct. One method is to remove the carb to check. Here is a trick to avoid that....Do this for 020,040,060 slot showing below the blades. Measure with calipers from the head of the speed screw to the screw boss & note the slot position of the screw [ horiz or vert ]. Write it down. These measurements can now be used to check T/slot position without removing the carb.
[4] If you are using the factory 10-14* initial, it is nowhere near enough for that cam & getting this correct is the first phase in getting this engine properly tuned.
[5] So report back with the timing info & we go from there. I am here nearly everyday. Below are improvements achieved when extra timing was added at idle.

 

[AR67GTX]

I think you should be getting a little more vacuum with that cam but I know the old 383 I once had did not respond well to a cam change. It wouldn’t hurt to check all the intake bolts and tighten if needed. Also check any vacuum hoses for cracks or breaks. You can try putting the accelerator pump link on the top hole but check the pump height per the rebuild instructions or FSM if you do. And I use to try to set my idle mixtures on the edge of the lean roll off but after dealing with some hesitation and exhaust odor from poor combustion due to a lean mixture, I now shoot for the middle between lean and rich roll off.

 

[HS 69 Charger]

Thank you @Geoff 2 . I will be out in the garage later this morning and get started. A couple questions:
1. Small port at Carb rear. Just making sure we are talking about the Vacuum fitting on the Intake manifold that currently feeds the Headlight canister (I don't have power brakes) and also feeds the ventilation pistons in the Heating/Cooling ducts. Previously, I was using the one on the distributor advance. I was planning to disconnect all of them and plug just to make sure I didn't have a leak influencing the readings.
2. Since I am still learning, I had just watched a YouTube (Muscle Car Solutions) recommended recently by another user on this forum. It was on the Transfer/Transition area so I wondered if I had too much of the idle adjustment messing this up. So I will start here.
3. The cam was a recommendation by the machine shop that did the heads back in 1990 when I was stupidly 29. I soooo wish I could go back and say no just stock.
4. On your step 4 you mention 10-14*. Is this vacuum or are you asking me the initial timing setpoint. My FSM says 5 degrees BTC for timing.
5. Lastly, I realized with all of this and the low vacuum, I never checked the rods at idle to see if they are fully seated. I will do that too.

 

[Rebelrouser]

After a bit of digging, I found the info on the Crane Cam installed in my car back in 1990. Now, as I hold my breath, you can tell me what comments you have on the CAM and if it is the influence of the lower vacuum I see at idle. I know nothing about cam specifications.

I should also ask what is the proper pickup point for my vacuum measurement. The carburetor has 2 lines. One for the Choke Pull off and one for the Distributor Advance.
And the back of the manifold has a large fitting for the headlight doors (line to canister) and a small port take off that runs the inside ventilation doors on the Heating/cooling ducts.

Thanks for additional information.
Martin

View attachment 1845105

If the cam is installed at 107 degrees intake centerline, and with the 228 duration on the exhaust the idle vacuum is normal. Raise the idle with the gauge connected to about 2,000 rpm steady and you should see 18 to 22 inches of vacuum.

 

[AR67GTX]

Hooking up to an intake vacuum nipple is providing full time manifold vacuum to the distributor so it would be pulling in vacuum advance at idle.

 

[HS 69 Charger]

Much progress. Learning so much from this forum (and a few YouTubes).

Initial:
1. Intake Manifold Vacuum fitting:
a. removed Heater/AC pneumatic line and blocked port
b. removed Headlight canister line and attached Vacuum gauge in place.
2. Distributor Vacuum advance hooked up to carb port to left of PCV hose inlet.
a. Disconnected at Distributor and blocked line during Vacuum Advance tests and then reconnected.
3. Vacuum Choke pull off disconnected and line plugged as this device is leaking and replacement is on order.
4. Pulled carb and measured relationship of throttle plate and transfer slot.
a. First good news is I finished the previous tuning with the slot exposed at about .064". High but not grossly high.
b. Came up with table to identify screw position Hrs on clockface vs transfer slot length. Also measured with caliper as starting point.
10oclock = 064, 9 = 060, 4 = 040, 11 = 020, 6 = 0 turning CCW
c. Also checked finish point previous day on Idle Mixture screws. L = 2 3/4 R = 2 5/8
d. Reinstalled carb with idle screw and mixture left at previous days settings so I could start the car.

Today's Tune
1. Started walking back Idle screw (closing off transfer slot) and increasing idle mixture. Gear in Park and Distr Advance attached.
Vac RPM Mixture Idle
15 800 NC NC This is starting point from yesterday's tune. Note with Vacuum on Manifold its now up at 15.
11 650 NC 10 to 4 (clockface) Change slot from 064 to 040 by backing out Idle screw. Note vac and rpm drop down. Rough idle
14 750 +1 NC Increase mixture screw to gain back RPM which is shifting Idle Fuel from slot to Idle screw
12 650 NC 4 to 1:30 Change slot to about 030
14 700 +1 NC Increase mixture screw to gain back RPM
Starting to reach limit of Mixture screw. When Placed in Drive it dropped to 600 and was rough. Without other changes (timing) it appears 030 is a bit too far.
15 750 NC 1:30 to 4 Change slot back to 040
Now placing in Drive runs about 650 and is fairly smooth. Smoother than I remember for a long time.

2. Timing
a. Vac Adv disconnected. Just over 5 degrees 700rpm 14"vac
b. Used hand vac pump. At 8"vac 8 degrees 750rpm 14-15"vac At 15" 22degrees 900-950rpm 17vac
c. Vac reconnected. 12-13degrees 750rpm 15"vac
d. RPM kicked up to about 1750 using Fast Idle Cam. Timing way past marker. Estimate 35degrees

3. Rods
a. I did validate rods are seated at idle and pop up during quick acceleration. Operation appears ok but have never tried different springs to see if it might be set to strong. I believe they have never been changed from original.

Test drive: Significantly smoother at stops (idle in gear). Dead stop acceleration occasional has hesitation. Acceleration from any speed above stop is fairly smooth. I didn't over test this but didn't notice any concerns.

Open to suggestions but planning at this point to drive it some and take note of Idle over time and also acceleration. Will pursue these after a bit of drive time. But this is Far, Far ahead of where I was before I started this endeavor.

So thankful for the help provided so far. i would not be at this point without all the info and suggestions.

Martin

 

[oldbee]

Sounding good,but,,,, too weak advance springs in distributer? It’s been a long time for me to remember & my FSM is at my youngest son’s.

 

[Geoff 2]

Martin,
The carb idle cct should always, repeat, always be dialled in before anything else is done. That includes main jets & total timing.

When vac increases at idle, it means the engine is burning the fuel more efficiently. A byproduct of this is increased idle rpm. All of this is good news.
Ok, now it is crunch time. Next step is determine what this engine needs for best idle, ie idle timing. Once this is determined, we go to the next step.
This is a very simple process: VA disconnected. Initial at or near factory spec, not critical. Warm up engine, chock wheels, put into gear. Loosen dist clamp. Slowly turn the dist CW [ this advances the timing ]. Keep going until you have the highest rpm. Toggle the dist to ensure highest rpm. Now, check what the timing is. With your combo, I am expecting between 25-40*.
Whatever it is, that is what your engine wants.
Report back with the results.

 

[HS 69 Charger]

Thanks @Geoff 2.
My biggest miss was the transfer slot position and how the initial idle screw position affected whether I was truly in the idle cct mode. Previously, I'm sure I wasn't. The second day I was a bit past but still getting some Idle Mixture adjustment. After your information, I was able to backup and then really set the Idle correctly. Of course putting the vacuum gauge on the right manifold port helped too.
A couple questions on results so far. For Geoff or anyone else to help me understand.
1.The final mixture with the best vacuum (best fuel efficiency) seems fairly rich as both mixture screws are out 4-5turns. Is this a product of the CAM wanting a richer mix, the engine getting old, 383s just ran rich, or today's fuel (note I am adding lead as I don't have hardened seats). Or is it all of the above. Is this normal for our cars or is mine on the excessive rich side.
2. Since I don't know what the original CAM selection was, based on the spec sheet, is this CAM for Street performance. Would it be considered a MILD upgrade or Aggressive. Was it for low end power or high end power. And does it sacrifice low end idle smoothness for this power. I would just like to know what it is driving that is different than the Stock CAM for my car.
3. Total Timing: As we head into timing and based on the few tests i ran before, I wanted to know if I am understanding how this part of the cct works.
Initial Timing: Spec is 5 degrees BTDC. With Vac Adv disconnected and at idle RPM I would expect the Centrifugal is basically off. Then I tested Vac Advance at 8 and 15" vacuum (again specs in book). These appear to match the intended specs in book although I would expect the 15" vac ran up the RPM and started a bit of Centrifugal Adv. Then lastly with it all hooked up, I set the Fast Idle Cam to about 1700RPM and so now you have Base Initial, plus full Vac Adv, plus much of the Centrifugal Adv. Just from book specs this is 5* (initial) + 12* (Vac Adv) + 17* (Centrifugal if up at 2500rpm). So about 35*. I'm just wanting to see if I understand this additive nature of Timing. Also, while Vac Adv adjusts during changing load (acceleration vs cruise) Centrifugal is purely what RPM are you at.

Hoping to confirm or fill in the gaps of my understanding so far.

Thanks Martin