Tuning with jets, Power valves and an O2 guage

Kern Dog · Feb 5, 2014

I have no suggestions on tuning the dual quad carbs other than to adjust them in tandem in small incremental steps. The guage reads what is happening almost instantly but I have found it can fluctuate a bit after an adjustment. I've had to adjust, watch the guage and wait to make sure my changes didn't go too far the other way from where I wanted.
Oddly, yesterday during a 52 mile round trip, it was running much richer at cruise. I still have the same #84 primary jets and 3.5 power valve. The only change was swapping to the Rev-N-Nator ignition box. The weather was colder than it was during the last test run. I have no choke on this carburetor. It ran great but read richer than before. This weekend I'm going to weld in a balance tube behind the collectors. The exhaust guy didn't feel like doing the balance tube when I had the pipes changed after switching to the TTI headers some years ago. I've dealt with too many Service guys with bad attitudes. I wonder what effect adding the balance tube may have on the A/F readings. I'm trying to tone down the raspy exhaust a bit and reduce some of the overall noise of the car. I'm obviously not a teenager anymore. The loud noise is getting to me these days!

Meep-Meep · Feb 5, 2014

62 Dart Convertible said:
I second that emotion, I'm in the same boat. Has anybody seen a guide on the order in which dual quads should be tuned? Mine is a factory dual inline set up with the progressive throttle linkage.

They are pretty forgiving because it's not an individual runner system. Start with idle mixture screws and throttle stop screws on both sets of primaries set exactly the same. What's important here is equal fuel distribution, and to check that pull plug wires to verify mixture strength by noting the RPM drop at each cylinder. My suggestion is to loosen all the wires on the cap end so you don't have to fight them off while the engine is running and pull them out of the cap rather than the plug. Reason is once the wire is pulled you are not holding onto 30 KV looking for a place to go. If you get little to no RPM drop on a cylinder or two it's likely lean at those cylinders. Then play with the mixture screws that are in proximity to the affected cylinder/s. Intake manifold temp plays a big roll here so make sure everything is at operating temp before you start diddling the screws. And I will add there is a little black art to this. I rely on a keen ear and never use gauges while doing adjustments.

62 Dart Convertible · Feb 6, 2014

I'm with you Greg on the loud exhaust. I used to love it years ago, but now the drone grates me. A balance pipe will definitely take some edge off it for you.

Thanks Meep. Good idea pulling plug wires from dizzy - I have held on to a bad lead once on a HEI - I could have won a disco dancing competition, but it f&$%#*g hurt!

Once cruising season is over (ie when your cruising season starts..), I will pull the heads and fit cometics, get new bigger but quieter exhaust and fit the afr and tune carbs...

bobtile · Feb 6, 2014

62 Dart Convertible said:
I'm with you Greg on the loud exhaust. I used to love it years ago, but now the drone grates me. A balance pipe will definitely take some edge off it for you.

Thanks Meep. Good idea pulling plug wires from dizzy - I have held on to a bad lead once on a HEI - I could have won a disco dancing competition, but it f&$%#*g hurt!

Once cruising season is over (ie when your cruising season starts..), I will pull the heads and fit cometics, get new bigger but quieter exhaust and fit the afr and tune carbs...

This is where we part company. If I thought I could run open headers on the street, I would. Drone on!!!

snakeoil24 · Feb 8, 2014

Tune back carb first and use a hat to get linkage to work properly. Dvorak has a hat for afb carbs. A single Quick Fuel will out run any thing with repalceable air bleeds.

bobtile · Feb 8, 2014

snakeoil24 said:
Tune back carb first and use a hat to get linkage to work properly. Dvorak has a hat for afb carbs. A single Quick Fuel will out run any thing with repalceable air bleeds.

I'm trying to keep the "cool factor" with the dual quad setup but make it perform as well as possible on the track. I think I will eventually be replacing that setup with a single carb. I know that will be an improvement.

- - - Updated - - -

snakeoil24 said:
Tune back carb first and use a hat to get linkage to work properly. Dvorak has a hat for afb carbs. A single Quick Fuel will out run any thing with repalceable air bleeds.

I knew I saw those hats somewhere, I just couldn't remember where.

Herr_Poopschitz · Feb 8, 2014

bobtile said:
This is where we part company. If I thought I could run open headers on the street, I would. Drone on!!!

Nothing like loud cars that run high 11s or slower. Don't be 'that guy'.

440beep · Feb 8, 2014

That's where the joy of electric cutouts come in. I always have my headers open, unless I see the black and white, then its stealth mode. I've never been stopped for open headers and usually get a thumbs up from the cops.

bobtile said:
This is where we part company. If I thought I could run open headers on the street, I would. Drone on!!!

snakeoil24 · Feb 9, 2014

Well nothnig is cooler looking that 2 AFB Carbs for sure unless you had a cross cramm wghich will run like a disaster on the Street. What I have found from listening to otehrs regarding the O2 meters is amazing. If you use the hat and o2 your results will be real good. Also remember if you put an aluminum wafer under the carbs you will keep them cooler and better results tuning. I am no racer, if your looking for racing knowledge their many people hear really know their stuff.

Kern Dog · Feb 17, 2014

Last week I welded in an H pipe to the exhaust. I'm aware that an X pipe is better but I don't have the ability to make one of those.
Instantly I could tell that the idle tone has softened. The irregular pulses seem to have been reduced a bit though the idle speed is the same. Here is where it gets odd: since the change to the Rev-N-Nator and the H pipe, The A/F readings went haywire!
My readings at a steady 40,50 and 60 mph went from in the mid 13.0 range down into the 11.0 zone. HUH ???
I'm going to map the readings again then reduce the primary jets again. I will report back.

krowbar · Feb 17, 2014

I've been looking at a few a/f ratio setups and will probably buy one soon. Where is the most practical place to put the O2 bung? I was thinking of putting it in the H pipe for ease of access. I also thought of buying an extra bung and putting one in each collector and plugging the one not in use. What will give the truest readings?

HEMI-ITIS · Feb 17, 2014

One on each side is much better than 1 in the "X" pipe.:blob1:

Kern Dog · Feb 17, 2014

The kit I got came with one bung. I had it installed in the RH collector then had the muffler guy add another to the left side.

coloradodave · Feb 17, 2014

bobtile said:
I have a dual quad setup and was wondering if anyone knew what would need to be done to get both of them in tune. They seem like they are working well by the way the plugs work, but as stated earlier, that can be misleading.

diamondbackengines.com/ has a pretty good primer on tuning dual quads. Go to the 'white pages' and you'll find a couple of articles there. Also, you can make a low dollar carb synchronizer by buying a Unisyn off ebay, a plastic carb hat from Summit, cutting a hole in the hat and using silicone cement to marry the two. This device allows you to adjust your linkage so that the butterflies of both carbs are synchronized at idle.
ALSO, snakeoil24, I beg to differ on running a crossram on the street. I have run a factory crossram with two 500 cfm Edelbrock carbs for several years without problems. I have manual chokes and yes, there is a few minutes of 'jazzing' the throttle until the manifold gets some heat in it, but after that it has very good manners. And yes, I do it for the WOW factor when I open the hood...

HT413 · Feb 17, 2014

coloradodave said:
and yes, i do it for the wow factor when i open the hood...

wow. Purrrdey.

snakeoil24 · Feb 17, 2014

coloradodave said:
diamondbackengines.com/ has a pretty good primer on tuning dual quads. Go to the 'white pages' and you'll find a couple of articles there. Also, you can make a low dollar carb synchronizer by buying a Unisyn off ebay, a plastic carb hat from Summit, cutting a hole in the hat and using silicone cement to marry the two. This device allows you to adjust your linkage so that the butterflies of both carbs are synchronized at idle.
ALSO, snakeoil24, I beg to differ on running a crossram on the street. I have run a factory crossram with two 500 cfm Edelbrock carbs for several years without problems. I have manual chokes and yes, there is a few minutes of 'jazzing' the throttle until the manifold gets some heat in it, but after that it has very good manners. And yes, I do it for the WOW factor when I open the hood...

Colorado immaculate set up. I hear you about the wow factor and reliable manners you are getting. The 500 CFM carbs i bet have a great deal to do with it. bigger is not as reliable.

Kern Dog · Feb 26, 2014

I'm still working on things over here but I keep halting myself from moving forward.
Not sure if it is my nature, but I have had a hard time feeling satisfied. I make the adjustments, drive the car then wonder if I should make bigger changes. I'm not happy with this cam. If all I cared about was having a straight line dragstrip animal, the cam would be fine. The car makes great power at mid to upper rpms. Idle quality is okay, not fantastic. It is a bit soggy from idle to about 3000 rpms. I thought by leaning it out to the desired a/f readings that it would feel more crisp at freeway cruising speeds. I'm doing about 2500 at 60 mph and 2800 at just under 70. The work with the jets, power valve, idle mixture screws and timing adjustments seem pointless if I decided to change the cam. Keep in mind that this Lunati wasn't chosen for street manners, it was chosen to try to stop the engine from detonating. Since that plan didnt work, I switched to these thicker Cometic head gaskets.
One low cost trick I may try is to advance the cam 4 degrees and then set the valve lash a bit wider. These 2 things will move the power band down a few hundred rpms and also make the cam act "smaller" I guess that means that afterwards, I'll be back tuning the combination again.

coloradodave · Feb 26, 2014

snakeoil24 said:
Colorado immaculate set up. I hear you about the wow factor and reliable manners you are getting. The 500 CFM carbs i bet have a great deal to do with it. bigger is not as reliable.

I had 750s on it and it ran OK but is much 'crisper' with the 500s. It's a street car and doesn't need 1500CFM. Thank you for the compliments everybody.

Kern Dog · Feb 26, 2014

Today I finally checked the cranking compression.
Before with the Fel Pro .039 head gaskets and nearly 11.0 to 1 compression I was at an average of 191. Now with the 10.07 to 1 ratio my average went down to around 160 !
I checked every hole twice. I had the battery charger on the battery to maintain an even charge. I was amazed that the cranking numbers dropped off so much compared to before.
I decided to start playing with the lash to see what effect it had on the cranking psi. Wow, what an eye opener! The Hot Lash specs are .020 IN and .022 EX. I normally set them .006 tighter (.014 & .016) when cold to account for the expansion of the aluminum heads. This time I set them cold to .022 IN and .024 EX. That is .008 wider spec. This raised the cranking compression to an average of 170.
I haven't driven the car yet. I figure I'd see how it feels after the lash adjustment. If it feels more responsive down low I might leave it as is as long as it isn't knocking.
I was really surprised to see what an effect the lash really had on the cranking compression

IQ52 · Feb 26, 2014

Have you checked with the cam manufa.............never mind............

Tuning with jets, Power valves and an O2 guage

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