AVS2 650 CFM on a 383-2, tuning help needed

[edbods]

Alright. I've had the AVS2 on for a while now and the first time I did it quick and dirty by hearing when I felt it sounded right. Seemed to go great. Then I got a new exhaust, and started messing around with it after installing the carb cheater to see the vacuum and AFRs. But if I set the AVS2 to a warm idle of 500 as per the AFB factory specs, it never seems to get more than 18.5 inHg at warm idle (or at least, on a 100F day with the choke open), but if I rev it at 1000 rpm it gets 20 inHg. But that seems like way too high an idle.
I've never really tuned a carb before till now so am I looking at the wrong thing?
I'm kind of leaning towards ignoring the factory idle speed value as my power steering seems to struggle when the engine rpm gets low enough. The wheel will get really hard to turn while stationary or while turning at very low engine speeds (with a fresh belt and very tight tension too).
On an unrelated note, now I know what fuel percolation is lol. A bit awkward when I was cranking the engine for what felt like forever outside the exhaust shop while people were staring before I figured out that I just had to depress the throttle a bit while doing that. This was all despite having a composite 1/2" spacer and fiberglass insulation on the steel line going into the carb. Methinks I need to get the intake valley gasket that blocks the heat crossover since I've got an electric choke now.

 

[CBODY67]

You can try increasing the hot base idle speed to 600rpm if it makes the power steering pump happier. Not a big change, especially with a/c.

Those quoted vacuum readings are really very good. Not "too high" at all, but what I'd term "normal". Is your "calibrated vacuum leak" supposed to decrease them?

It has been my experience that about 1/3 throttle usually works fine for cold and hot starting on my Chryslers (and other carbureted vehicles). Some carbs are happy to start with no throttle, but some of them do not like to do that. Have to learn what the vehicle likes, for best results. Then tweak from there.

Take care,
CBODY67

 

[edbods]

At the moment the carb cheater has the auto tune function (the thing that actually adjusts extra incoming air) turned off so it's not adding extra air, only picking up readings from the engine. The way it's meant to be used is you first use it to tune your carb with better precision than hearing or butt dyno ever could, then enable the auto tune function to cover real-time adjustments on the fly. But unfortunately a lot of people just see it as a band-aid fix for a poor tune, even the guy that created it says it's not.
If my car has only been sitting overnight and I start it I can get it to run without touching the throttle. It seems to be only on very hot days that it'll struggle with a warm/hot start so I just have to remember to hold the throttle down a bit.
But if those readings are good then that's a relief. In my panic from the fuel percolation I probably ruined the tune, it's running rougher with a vacuum level around 13-15 now so I have to re-adjust. I just wasn't sure about whether I should really set the warm idle at 1000 rpm if it meant getting 20 inHG vacuum.

 

[CBODY67]

no need to get to anywhere close to 1000rpm on a reasonably stock engine, period. In the old repair manuals (when cams were milder than in the 1970s), the "aim" was 18" Hg at hot base idle. Of course, when the rpm was increased a bit and ign timing increased, it would go up toward 20" Hg. Personally, I would just adjust the hot base idle speed and mixture to the best mixture at about 600-625rpm in "N"/"P" (as the power steering pump has capacity issues at the lower rpm.

What has been termed the "Lean, Best Idle" method is where you set the idle speed to specs and then adjust the mixture screws to attain the highest rpm level. Resetting the speed screw as needed. This should also yield the highest vacuum levels, too. Many would stop there, but to verifyst" is with a dwell tachometer. Adjust each screw "lean" until a 20rpm drop in idle speed is attained, then return to the prior, highest rpm level at that mixture setting. Same with the other idle mixture screw. As the rpm dropped, that is the verification that the mixture is at the optimum setting.

As to the idle speed itself, I devised my "shadetree smell and feel" method. After all of the things mentioned above have been done, I would THEN firmly apply the parking brake, with the foot brake applied, too, I would then put the vehicle into "D", release the foot brake (parking brake still applied) carefully, then go to the back of the car and feel the pulses sfrom the exhaust pipe. Just when the flow is smooth and not segmented, THAT is the idle speed in gear that was my new target. Even if the speed in "N"/"P" was higher than factory specs. As I was checking this with the palm of my hand, any

 

[Fury1969WI]

A friend and i both have AVS carbs on our Mopar and noticed the same hot start issues. I noticed my car likes a partial throttle when hot and i let it sit for >15 minutes (a good heat soak i guess). This is from a 1973 Chrysler owners manual:

 

[413]

What year is the engine? Does it have stock pistons?

Definitely raise the idle speed.

Don't block the heat crossover, it will cause you many problems with driveability.p, stumble bog.

Watch this video below about the heat crossover, why a carbureted car needs it open and working and why a EFI needs it blocked

Go to you tube and search this title:
"Why your TBI EFI classic car never seems to runs right and what you can do about it"

 

[CBODY67]

I have had friends who blocked the heat riser passage (for hot rod performance orientations, usually). When I swapped engines to one with factory aluminum heads that were for an OEM EFI engine, THEN I noticed some things I had not noticed before.

Had to tweak/re-calibrate the electric choke thermostat from what it was before. Same carb and aluminum intake with an open carb heat passage. Until heat migrated into the aluminum intake (from the aluminum heads), drivability was not totally to where it was before the aluminum head motor was swapped. Again, same intake and carb on both engines. Same cam and open element air cleaner, too.

Any EFI engine has the capabilities to tailor the fuel mixture to the engine operating parameters, cold or hot or anywhere in between. Carburetors do not have that built-in capability, needing specific choke tweaks to work their best. So carb'd motors need the heated plenum and EFI motors do not.

Enjoy!
CBODY67

 

[edbods]

Thanks guys. I thought that especially with the temps we see here since we never see snow that the crossover wasn't really needed. Also CBODY67 I think your 2nd reply got cut off at the end.
Although I do see quite a few people have blocked their crossover without further problems with cold driving (at least the ones that don't live in areas that see freezing temps).

 

[edbods]

What year is the engine? Does it have stock pistons?

Definitely raise the idle speed.

Don't block the heat crossover, it will cause you many problems with driveability.p, stumble bog.

Watch this video below about the heat crossover, why a carbureted car needs it open and working and why a EFI needs it blocked

Go to you tube and search this title:
"Why your TBI EFI classic car never seems to runs right and what you can do about it"

It's a 1967 383. Stock pistons.
Also come to think of it, I think I should've adjusted the idle speed while the car was in drive rather than park, because it definitely started struggling when I put it in gear.

 

[CBODY67]

Our '66 Newport 383 2bbl had no issues idling at 550rpm with the a/c om in gear. Sometimes, I might end up at 575rpm, but the factory specs worked well on that car. but that engine had the OEM 252/252.390 cam in it. Last year for it. The 256/260 cam after that.

 

[stain]

What is your timing? This gets ignored A LOT when setting idle speeds and curing hot start problems.

 

[Toolmanmike]

Alright. I've had the AVS2 on for a while now and the first time I did it quick and dirty by hearing when I felt it sounded right. Seemed to go great. Then I got a new exhaust, and started messing around with it after installing the carb cheater to see the vacuum and AFRs. But if I set the AVS2 to a warm idle of 500 as per the AFB factory specs, it never seems to get more than 18.5 inHg at warm idle (or at least, on a 100F day with the choke open), but if I rev it at 1000 rpm it gets 20 inHg. But that seems like way too high an idle.
I've never really tuned a carb before till now so am I looking at the wrong thing?
I'm kind of leaning towards ignoring the factory idle speed value as my power steering seems to struggle when the engine rpm gets low enough. The wheel will get really hard to turn while stationary or while turning at very low engine speeds (with a fresh belt and very tight tension too).
On an unrelated note, now I know what fuel percolation is lol. A bit awkward when I was cranking the engine for what felt like forever outside the exhaust shop while people were staring before I figured out that I just had to depress the throttle a bit while doing that. This was all despite having a composite 1/2" spacer and fiberglass insulation on the steel line going into the carb. Methinks I need to get the intake valley gasket that blocks the heat crossover since I've got an electric choke now.

when you have a hot soak restart issue, do a little diagnosis if you can. Look down the carb and see if it has fuel. If it doesn't have a steady stream from the accelerator pump nozzles, your percolation issue is real. I have heard fuel actually boiling inside the carb when I shut it off hot. It doesn't take long and it has evaporated out of the bowls and excessive cranking is needed to fill the carb back up again. The evaporation can also happen after a long set in the garage from a few days to a week. Many have had success with a small electric charge pump that fills the carb back up whether cold or warm. Here's a link. Electric priming pump for fuel evaporation issues. Hook it up with a fused circuit with a key on feed. You only need it when you start it cold or hot soak warm but it can be used in case your mechanical pump fails.

 

[edbods]

What is your timing? This gets ignored A LOT when setting idle speeds and curing hot start problems.

I wish I wrote it down somewhere when I set it, it was either 10 or 12.5 BTDC

 

[Fury1969WI]

It's a 1967 383. Stock pistons.
Also come to think of it, I think I should've adjusted the idle speed while the car was in drive rather than park, because it definitely started struggling when I put it in gear.

Agree, generally set idle with trans pump engaged; neutral works.

 

[edbods]

Wouldn't neutral be the same as park though? RPM would still idle higher than while in gear.

 

[Fury1969WI]

Wouldn't neutral be the same as park though? RPM would still idle higher than while in gear.

unless someone changed things that 727 pump runs in neutral but not park. This is why you check fluid level in neutral. in gear works for setting your idle if you can do that safely.

 

[edbods]

Ahhh right never knew that, thanks!

 

[CBODY67]

I believe the fluid schematic in the FSM details the various gear selection positions and related line pressures. "P" is only running "lube pressure", as "N" runs "operating pressure".

 

[WissaMan]

I also concur with keeping the crossover open for better drivability and tunability. One of the problems that doesn't always get thought of is fuel wetting and puddling in the intake which can make you chase your tuning. What happens is during WOT the intake chills and fuel droplets that hit the intake runners wet the intake walls instead of vaporizing. This causes the AFR to trend lean. Then once the walls are fully wet, the fuel starts getting dragged along the runners into the cylinders causing it to go rich. Your carb cheater may be able to compensate for that, but the fuel that's getting pulled into the cylinders will be (relatively) big blobs which isn't good for efficiency.

On my 440 I took a half-way approach. The PO had installed a valley pan that had the ports blocked off (and I was experiencing this exact phenomena) so I punched 1/2" diameter holes in the pan. The idea being to allow some exhaust through to provide heat, but not so much that it gets sizzling hot. It seems to work pretty well this way for me, though I have to wonder if over time those holes will get burnt out progressively larger from the hot exhaust.

 

[edbods]

Thanks yet again guys! Always learning something here. I think for now I'll just hold the throttle slightly open on a hot start and then see if I want to get the blockoff valley pan and drill holes in it. When I get around to it, I'll also post screenshots of my tuning logs - it's cool being able to tweak things based on what can be seen.
For now though, I've got to take out the original radiator and reverse flush it, there was quite a bit of rusty flakes in it and more than likely the cause of it overheating on the highway then cooling down once back on surface streets and semi-regularly spitting out coolant...