# Dual quad jetting questions



## michaelfind (Dec 14, 2018)

I have a stroked 400, now 467ci with moderately ported 6X heads. I am running two 600cfm edelbrocks on top of an edelbrock P65 dual plane intake manifold. Break in is complete and it is running fairly well, but I'm sure it is not running to it's full potential. I have the adjustment kits for the carburetors with the charts in them to make richer or leaner etc. However, I'm completely new at the dual quad experience. I assume these charts are based on use for one carburetor set ups. Do I need to be jetting things more lean than if running one carburetor? My plugs look a little rich but not awful. Any experiences to share? Thanks for your help.


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## Lemans guy (Oct 14, 2014)

I use two wide and 02 sensors in the exhaust and can read the AFR as I drive. You could use one or even a portable AFR gauge to see what you are actually getting throughout the band.

of you know this but saying it out loud helps, the engine really does not know if one has a 4 barrel, an EFI dual quads or whatever. If you can deliver the correct AFR at each stage than that is the ticket. Not a dual quad expert, but I helped a friend recently with dual quads, it was too rich, I bet you are as well.....try a little leaner, might help...AFR and wide and really is the best way


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## michaelfind (Dec 14, 2018)

Lemans guy said:


> I use two wide and 02 sensors in the exhaust and can read the AFR as I drive. You could use one or even a portable AFR gauge to see what you are actually getting throughout the band.
> 
> of you know this but saying it out loud helps, the engine really does not know if one has a 4 barrel, an EFI dual quads or whatever. If you can deliver the correct AFR at each stage than that is the ticket. Not a dual quad expert, but I helped a friend recently with dual quads, it was too rich, I bet you are as well.....try a little leaner, might help...AFR and wide and really is the best way


Thanks for the reply. I know wide band AFR is probably my best answer, but I'm reluctant to install one, just for the sake of keeping the appearance more old school technology. Is there really a portable unit I can use just for tuning purposes without having to weld in the o2 sensor bungs?


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## BearGFR (Aug 25, 2008)

michaelfind said:


> Thanks for the reply. I know wide band AFR is probably my best answer, but I'm reluctant to install one, just for the sake of keeping the appearance more old school technology. Is there really a portable unit I can use just for tuning purposes without having to weld in the o2 sensor bungs?


Yes, but all of them require a weld-in bung to use. The difference is whether the gauge itself is permanently installed or not. I have a portable one, an Innovate LM-2 that I started with. 
Innovate LM2

Not too long ago I put in a permanently mounted gauge, an AEM-X300 that I like much better.
AEM UEGO Digital Air/Fuel

It's "always there", easier to read, etc. It also supports data logging, if I ever decide add the controller for that.
I mounted it along with a brace of other AEM digital gauges on a panel just above my console.
I have oil pressure, coolant temp, trans temp, and air/fuel. Sorry for the one photo that's out of focus.
As you can probably tell from the missing ash tray, I took these as I was in the process of finishing up the installation so the interior was still dirty from me crawling around.

Bear


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## michaelfind (Dec 14, 2018)

Thank you. That is very helpful. Is it worth it to weld in a bang for each exhaust pipe, or can I can accurate results with only one?


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## michaelfind (Dec 14, 2018)

michaelfind said:


> Thank you. That is very helpful. Is it worth it to weld in a bang for each exhaust pipe, or can I can accurate results with only one?


stinking autocorrect


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## BearGFR (Aug 25, 2008)

michaelfind said:


> Thank you. That is very helpful. Is it worth it to weld in a bang for each exhaust pipe, or can I can accurate results with only one?


I'm only using one side, and it's working fine for me. If there's "something weird" about your engine that causes the mixtures on each cylinder bank to be different enough to matter, then you of course won't detect that using a bung in only one side (and a single gauge). If that's actually happening, then you'd be in a situation where you'd have to try to correct it through "stagger jetting" (different jets on each 'side' of the carb) and maybe fiddling around with trying to modify the air flow through the intake manifold. YMMV of course but personally I don't think that situation has a high probability of happening.

My .02 - keep the change 

Bear


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## GTO44 (Apr 11, 2016)

michaelfind said:


> Is there really a portable unit I can use just for tuning purposes without having to weld in the o2 sensor bungs?


You can use one of these kits if you dont want to weld... its a clamp on version. Only have to dill one hole. 









Hooker Headers 71014302-RHKR Hooker Clamp-On Oxygen Sensor Bungs | Summit Racing


Free Shipping - Hooker Clamp-On Oxygen Sensor Bungs with qualifying orders of $99. Shop Oxygen Sensor Mounting Clamps at Summit Racing.




www.summitracing.com





We use the ones that come with the Holley Sniper kit and other efi conversion kits. They work good, havent had any leak yet.

Then you could buy an afr gauge with a wideband 02 senson. Tempararily hook it up for tuning. Then plug the hole and remove the gauge until the next time you need it.


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## Lemans guy (Oct 14, 2014)

All good info from the gang...portable ones work, I have found that if you use a portable one....I have one also...you can add a piece of hard pipe, like small fuel line about 18” or two feet long and push it in the tailpipe. It will then give the same AFR readings at idle that the 02’s give just after the header. If you don’t extend it in that far idle circuit readings,...which is up to about 2500 RPM’s...will read very lean because of the ambient air near the tailpipe end. But your reading for main jets at cruising above 2500 will be accurate.

You can use portable one, use a bung with one wide and, or tap both for two wide bands. You can also hide the meter inside a glove box or some other creative place. Pair it with a vacumn gauge and you can tell everything that your fuel system is doing and when...

so you can do this or run without it,....Imlove them, more efficient no guessing better performance, no washed down cylinders or wasted gas,....tune it right it, runs smooth and feels as good as fuel injection!


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## PontiacJim (Dec 29, 2012)

michaelfind said:


> I have a stroked 400, now 467ci with moderately ported 6X heads. I am running two 600cfm edelbrocks on top of an edelbrock P65 dual plane intake manifold. Break in is complete and it is running fairly well, but I'm sure it is not running to it's full potential. I have the adjustment kits for the carburetors with the charts in them to make richer or leaner etc. However, I'm completely new at the dual quad experience. I assume these charts are based on use for one carburetor set ups. Do I need to be jetting things more lean than if running one carburetor? My plugs look a little rich but not awful. Any experiences to share? Thanks for your help.



Do it old school, seat of the pants. 600CFM shouldn't be too much.

Are you running the carbs in unison or progressive?

If progressive, did you shut down the idle mixture screws on the second carb? These will be providing fuel and can cause a "rich" situation. Primary throttle plates cracked open or shut closed on the second carb IF running progressive?

Have you synchronized the carbs - ie match vacuum readings for both? Check out this You Tube video on how to make your own "tool" to do this. I myself bought all the parts shown to make one of these for my Edelbrock AVS2 carbs on my tunnel ram. I know you don't have a tunnel ram, but it would seem to me the principals would still apply - adjusting one carb at a time.






I would not mess with the jetting just yet.  You don't want to go too lean either. Just for fun, I would try a hotter spark plug, go 1 or 2 ranges hotter and see what you get.

Maybe play around with a heavier spring on the power valve. 

Here is another post that may be of help.









Carter edelbrock dual quad


Hi Iv got two 600 edelbrock carbs. I want to run them as a dual quad on a Pontiac 455 with p65 intake. Compression is 9.5:1, cam is a raiv. I firstly want to try to use a 1:1 parallel linkage. Where should I start with the tuning? What jets/metering rods? What power valve Spring? What...




www.hotrodders.com





Timing. What are your settings? You may be able to do some advancing of it and improve things.

You can use an AFR meter, but I would do some seat of the pants dialing in first making one adjustment at a time.


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## michaelfind (Dec 14, 2018)

PontiacJim said:


> Do it old school, seat of the pants. 600CFM shouldn't be too much.
> 
> Are you running the carbs in unison or progressive?
> 
> ...


Thanks for the link and the video. That video is great. I'm completely new to multiple carburetor set ups and I did not even realize such a tool had been invented!

I'm running in unison. My timing is done per Lar's papers, so that I am at total advance of 36 (all in around 2900), initial of 18 without vacuum advance, and about 32 with vacuum advance connected to manifold vacuum. I've experienced some pinging when more advanced so I don't want to go any further advanced. I am already using Octane Supreme added at 4 ounces per gallon of 93 octane pump gas. Hey, this gets expensive quickly. But, the pinging scares me and must be eliminated. I calculate to be around 10:1 compression, maybe a tad higher, so I know gasoline/octane will always be an issue. Thanks for you great write up on that as well. Along those lines, I am afraid of going too lean in the mixture or getting to hot on the spark plugs because those factors may bring back the pinging. I may experiment a little more with seat of the pants and plug reading, but will probably chicken out and eventually install the AFR gauge (in the glove box as suggested above) so that I don't accidentally damage the motor as I'm tuning.


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## armyadarkness (Dec 7, 2020)

Nice to see fans of the AVS2 in here. I put one on my C3, with the AEM AFR and I bought the tuning kit, and I really love the carb. Changing jets and tuning can literally be done in under 10 minutes, without making a mess.


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## Lemans guy (Oct 14, 2014)

Good info from PJ as usual,...by the way I also use a PLX air fuel portable. It works on Bluetooth...

so you can use a temp hookup on your tailpipe or a permanent 02 sensor ...either way you read the AFR on your iPhone or iPad as you are in the garage or driving. You can put the iPhone in a mount and just drive and read the AFR....no need for any permanent gauge if you don’t prefer.....

following Lars is the best way, I do the same. One though you can do is get Lars to send you one of his vacumn correctors if you are running an original points dizzy. I use them on all the points size dizzy’s I curve. Curved a 327 1968 Corvette yesterday with one.

it will knock your vacumn down to 10 degrees, cut 4 degrees with what you are running now. That 4 degrees can help eliminate the pinging as you accelerate. 4 degrees isn’t much but it is enough to ping. On today’s gas you only want 8 to 12 degrees of vacumn advance.


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## Lemans guy (Oct 14, 2014)

Also with your 18 base and 10 degrees of vac hooked to full manifold vac will give you a nice idle at 28 degrees......if you cam is hot it will run smooth and cool there....yes it can take more, but not necessary.


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## PontiacJim (Dec 29, 2012)

michaelfind said:


> Thanks for the link and the video. That video is great. I'm completely new to multiple carburetor set ups and I did not even realize such a tool had been invented!
> 
> I'm running in unison. My timing is done per Lar's papers, so that I am at total advance of 36 (all in around 2900), initial of 18 without vacuum advance, and about 32 with vacuum advance connected to manifold vacuum. I've experienced some pinging when more advanced so I don't want to go any further advanced. I am already using Octane Supreme added at 4 ounces per gallon of 93 octane pump gas. Hey, this gets expensive quickly. But, the pinging scares me and must be eliminated. I calculate to be around 10:1 compression, maybe a tad higher, so I know gasoline/octane will always be an issue. Thanks for you great write up on that as well. Along those lines, I am afraid of going too lean in the mixture or getting to hot on the spark plugs because those factors may bring back the pinging. I may experiment a little more with seat of the pants and plug reading, but will probably chicken out and eventually install the AFR gauge (in the glove box as suggested above) so that I don't accidentally damage the motor as I'm tuning.


Pinging is a bad thing as you know. This is why I did not suggest to go leaner at this time. I saw your post over at PY and the jet suggestions. I would prefer to go a bit richer than not as a richer mixture can ward off some pinging as the rich mixture can add to cooling. You will find it may be a balancing act to get the carb dialed in at a perfect setting - it isn't EFI. So trying to get a good mixture at idle and cruise will require playing around, and then you want richer when you mash the gas and wind it out. EFI/Throttle bodies and the like have the advantage here, but with a carb, its more of a balance that may not be perfect, but in a range of acceptable, with the key to prevent pinging/detonation.

Check out this Compression/Octane requirement chart and the recommended amount to add to your gas using the Octane Supreme.



Octane Supreme Specs



The "tool" to sync the dual carbs was new to me when I saw the video. The guy in the id lives nearby and I go by his house/truck everyday. I have seen him run his truck at the drag strip. I bought all the parts to assemble the "tool" from Summit. I knew about sync'ing the multi-carbs on some of the foreign types and motorcycles. Never heard anyone using on dual fours, so this will be a first for me as well when I set my carbs up - can't hurt. LOL 

10:1 compression is high for iron heads, not so much for aluminum heads. So you will definitely need that octane booster. *Lemans guy *has covered what you may want on the timing and bring it down to 32 degrees Total. 36 in my opinion is a little high for open chamber heads unless running race gas. So I would shoot for 32, and maybe try 34 as a comparison. You are not really losing any power, and may actually gain power because the air/fuel mixture is burning better and not going into detonation mode - which you may not even hear.

You did not say what ignition system you are using. I like a good hot aftermarket spark, like what you get from an MSD box. You get multiple spark at the lower RPM's which can aide in burning the rich mixture at idle and lower RPM's. You can read up on them if you are not already running this. I have the MSD6AL unit that will go into my car as it has the built-in rev limiter that you can set so as not to over rev your engine. I used the MSD6 on a very rich running 2x4 409CI I built. It had the Mallory dual point distrubutor, 40,000 volt coil, and stock Champion spark plugs. I added the MSD6 and purchased a set of JC Whitney multi-electrode spark plugs said to burn better than regular plugs. Without the MSD and the JC Whitney plugs, the stock plugs would foul out rather quick if I wasn't constantly "blowing out the carbon." Installed the MSD & multi-electrode plugs and never had a problem fouling out plugs and the engine ran smoother - so I am a supporter for the MSD box.

If you are already having pinging, then using a hotter spark plug may make it worse. I was going off of the fact that you said the carbs were running rich as shown on the spark plugs. So a step or two may have helped burning this up. But, I would not rule out trying 1 step hotter than stock to see how the engine reacts/feels. You can also experiment with plug gap. This can sometimes make a difference. Don't gap based on your ignition type, gap to what runs best. I would try a tight .030", and then go up .05" up to .045" if you have electronic ignition. The wider the gap, the more energy required to jump the gap. The higher the cylinder pressures, the tighter the gap. I like .035" - period. But sometimes adjusting the plug gap can make a difference and may be worth a try.

Make sure you have a pair of good air cleaners that flow well. Those little aftermarket chrome air cleaners with the paper elements look cool, and I have used them, but getting good airflow can be had with a better brand of filter like the K&N elements. Restricted air flow affects your air/fuel ratio's and their readings.

A cool engine temp will also be of help in warding off detonation issues. I have used the Redline product "Water Wetter" and it seemed to drop engine temps down a bit - nothing crazy, but it did seem to help. Not expensive and can be had at most auto stores.

I do have an AEM brand AFR meter I will be installing on my build, but I will first do the "seat of my pants" tune on the engine/carb before applying it. I rather do my tune and run it first, then see what I actually have. I can tweak it from there. I think they have a place, but you can also go crazy trying to get your entire RPM range and throttle application on a perfect note. Some carbs are far more adjustable and lend to this tuning, while others are a little on the basic side and you can only go so far with them in dialing them in.

I purchased the AVS2 carbs for my tunnel ram set-up. The AVS2 had better features, one being the adjustable secondary air valve like a Q-jet. I was going to go with the "typical" Edelbrock AFB's until I began to read and watch the videos on the carb. Hopefully they perform as advertised.

So I would adjust that timing as suggested. Then start toying with the carb, first with some of the basic adjustments before swapping jets.


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## michaelfind (Dec 14, 2018)

PontiacJim said:


> Pinging is a bad thing as you know. This is why I did not suggest to go leaner at this time. I saw your post over at PY and the jet suggestions. I would prefer to go a bit richer than not as a richer mixture can ward off some pinging as the rich mixture can add to cooling. You will find it may be a balancing act to get the carb dialed in at a perfect setting - it isn't EFI. So trying to get a good mixture at idle and cruise will require playing around, and then you want richer when you mash the gas and wind it out. EFI/Throttle bodies and the like have the advantage here, but with a carb, its more of a balance that may not be perfect, but in a range of acceptable, with the key to prevent pinging/detonation.
> 
> Check out this Compression/Octane requirement chart and the recommended amount to add to your gas using the Octane Supreme.
> 
> ...





Lemans guy said:


> Also with your 18 base and 10 degrees of vac hooked to full manifold vac will give you a nice idle at 28 degrees......if you cam is hot it will run smooth and cool there....yes it can take more, but not necessary.


Great advice as always guys. Thank you. Yes, the recommendations I got at PY are much more lean than what I'm running right now, so I'll hold off on those suggestions unless indicated later.

I guess I may be overdosing my fuel with Octane Supreme according to that chart. Good to know I may be able to reduce the recipe and cut some costs. Part of my problem was that I kept hearing a mystery noise at around 3000 RPM. I run an MSD 6AL with a MSD blaster coil and a Pertronix billet distributor with the ignitor II inside. It looks fairly original and I don't have to remember to check dwell. My MSD is hidden under the front fender as someone on this site has done and I thought what was a clever idea. I also have the remote adjustment knob for the MSD hidden in my glovebox. This allows for timing adjustments as you drive or idle. My mystery noise sounded a bit like pinging and always kicked in around the same RPM. I've never run an edelbrock, much less two edelbrocks, so I was thinking it was the secondaries opening and getting really lean with subsequent pinging. It continued to happen, even as I turned down the timing adjustment knob. I thought I must be running much more compression than I realized. So, I kept increasing my Octane Supreme recipe. Turns out, that noise was my stinking alternator belt. I know that sounds ignorant, but it was not the typical squeal or chirping that I associate with a slipping belt. It sounded like a clatter or pinging. I got things tightened down properly and I think I have that problem solved. Jim, I have read your suggestion on the top cog belts too and have one of those ordered for a spare or replacement if slipping returns.

I'm currently running some copper core NGK plugs with heat range of 8. I think that was recommended by Butler performance. I have them gapped at 0.35. So far, those are the only plugs I have used.

My air cleaner is the standard edelbrock foam element that covers both carburetors. It does not seem very restrictive but may be more so than I realize. It did comes used with the whole set up that I purchased off ebay (manifold, carbs, air cleaner).
I would love to find some clones that look more like the real Pontiac SD air cleaners for the dual quad set ups. I have no idea if that is even possible with the P65 set up. The carburetors may be too close together.

I'll start with timing as you and LeMans guy suggested and go from there.

Thanks again.


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## Lemans guy (Oct 14, 2014)

I run those same plugs and heat range, Butler had recommended to me as well and I like the .35 gap as well. You are all over it and will get it dialed in. Food luck and let us know how you do...


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## lust4speed (Jul 5, 2019)

Possibly the simplest answer to going to 2-4's is each carb sees half the air of a single carb. Nothing matters but air flow and that will be half to each carb (at least in a perfect world). If engine is turning 4,000 RPM then each carb is acting like the engine is turning 2,000 RPM. If jetting is correct for a single carb, then jetting will still be correct for two of them.

How are you checking plugs? If the engine is allowed to idle at all before plugs are checked then they won't reflect actual heat conditions. Have to go back to the 1960's method of hauling down the expressway under power and hit neutral and cut the ignition and pull plugs along the roadside. We all did it before the widespread use of the AF meter, and it got us by. It would be very easy to have the idle screws out and running a rich idle and be on the ragged edge of lean with your foot in it.

I had the Offy setup with two older 650 AFB's and it was a trouble free setup with good power and much better than expected mileage running straight linkage with both opening together. I decided to go back to a totally stock looking engine compartment and sold the setup to a friend. I missed it and started looking for a replacement to go on my '65 Cat Safari wagon, and have now found and fixed up an Edelbrock dual quad manifold with a pair of newer Edelbrock carbs.


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## michaelfind (Dec 14, 2018)

lust4speed said:


> Possibly the simplest answer to going to 2-4's is each carb sees half the air of a single carb. Nothing matters but air flow and that will be half to each carb (at least in a perfect world). If engine is turning 4,000 RPM then each carb is acting like the engine is turning 2,000 RPM. If jetting is correct for a single carb, then jetting will still be correct for two of them.
> 
> How are you checking plugs? If the engine is allowed to idle at all before plugs are checked then they won't reflect actual heat conditions. Have to go back to the 1960's method of hauling down the expressway under power and hit neutral and cut the ignition and pull plugs along the roadside. We all did it before the widespread use of the AF meter, and it got us by. It would be very easy to have the idle screws out and running a rich idle and be on the ragged edge of lean with your foot in it.
> 
> ...


I like your set up, that looks good.

thanks for the explanation, that helps me think more clearly about the whole issue

I'm not checking the plugs the right way. I'm letting it idle as I pull back into my shop, so I'm certainly not getting accurate results.
I ordered an AFR through summit and plan to install it this weekend if nothing else has to be fixed around the house. I'll post what I learn from the AFR gauge.


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## Jim K (Nov 17, 2020)

Greetings Michael,
I'm also running Eddy's on a dual quad set up. 1403 as secondary, 1404 (electric choke) as the primary on my 428. 500 CFM carbs with an Offy low rise intake. Everyone in front of me has given good points and advice. An AFR will definitely help you. Just a few things to consider I didn't see mentioned.
Altitude plays a big roll in how you set up your jets. That's all in the manuals for the carbs. I'm at 5000 ft altitude and definitely had to lean out my jets. eddy makes .077" jets for the secondaries for dual quad set ups.
Make sure you have the right step up springs based on your idle vacuum. Springs set to 1/2 idle vacuum, or as close as you can get, are definitely necessary. (all in the manual)
eddy's seem to be prone to an off idle stumble. I corrected mine by ordering their power piston nozzle kit and going with the largest nozzles.
Eddy makes a power piston with a stiffer spring they put in the 750 CFM carbs that helps with the off idle stumble also. One other thing you can do is to either sand, or file down, the little weight that rests on top of the check ball in the power circuit (under the power piston nozzles). This just means less pressure needed to raise the check ball and get fuel out the nozzles quicker.
One thing to know, if your are running a pretty "hot" cam with more than factory overlap, your AFR reading will tend to show richer than what the ratio actually is. This is mainly due to the extra over lap between cylinders.
I went with the 500 CFM's for a couple of reasons.
as Lust4 mentioned, air velocity takes a hit when both carbs are open. Going small on the CFM keeps velocity a bit higher giving a better vacuum signal to the ventures resulting in better bottom end response.
even though my set up is progressive, I'm using both idle circuits since i have over an 8" spread between the carbs to help prevent a possible lean condition in the front cylinders at idle. It also helped me sync the carbs easier. There are two schools of thought on this. Below is my set up.


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## michaelfind (Dec 14, 2018)

I appreciate all the great advice here and I'm getting closer to having things gradually jetted correctly. I'm at about 800 feet, so our elevations are pretty different. Still, I'm curious what you are running in your eddy carburetors for rods and jets. 

Currently I have the following:
front carb - primaries .100 with 7052 rods and blue springs; secondaries .083

rear carb - primaries .098 with 7352 rods and blue springs; secondaries .083

The reason the carburetors are not jetted identical is because I'm using what I have available in the respective tuning kits, 1405 and 1406. I had to special order the .083 jets and may need to order the .077 jets to get things just right. I'm still a bit rich, running low 11 on AFR at WOT.


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## Baaad65 (Aug 29, 2019)

I didn't want the afr gauge showing either so have it in the glove box and when I need it I have velcro on the door.


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## michaelfind (Dec 14, 2018)

That's clever. I like it. I mounted mine in the back of the reproduction, plastic, glovebox. I initially cut a hole on the side facing toward the driver. It was perfect...until I tried to close the glovebox door and the stop brace hit the gauge. 😕


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## lust4speed (Jul 5, 2019)

Way back I borrowed a friends Innovate dual channel AFR portable meter. After a week of tuning and never seeing any difference in left and right readings and trying to observe and average numbers from two readouts, I went with a single readout AEM gauge when I made a purchase. I also converted my gauge where it plugs into the cigarette lighter, and uses a temporary mount on the steering column for setting up the jetting. I just pull everything back off and screw the plug in the hole in the header.

I'm still looking for the sheet that had my jet sizes, but going from a vague memory it looks like you might be jetted a little lean in the primaries and pretty rich in the secondary's. Off hand, I'd probably lean out the secondary's and leave the primaries alone for now. What are your cruise readings under light to medium load and maybe 2,500-2,800 RPM?

Tough call on your spark plug range because 8 is a pretty cold plug but your compression is high. On my 670's and 9.32:1 compression I run 6 on the NGK plugs. While your 10:1 compression seems like it calls for a little cooler plug, the physical results sure look like you should go a couple numbers hotter. Wallace Racing has a great sparkplug reading tech page: Wallace Racing plug reading.


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## michaelfind (Dec 14, 2018)

lust4speed said:


> Way back I borrowed a friends Innovate dual channel AFR portable meter. After a week of tuning and never seeing any difference in left and right readings and trying to observe and average numbers from two readouts, I went with a single readout AEM gauge when I made a purchase. I also converted my gauge where it plugs into the cigarette lighter, and uses a temporary mount on the steering column for setting up the jetting. I just pull everything back off and screw the plug in the hole in the header.
> 
> I'm still looking for the sheet that had my jet sizes, but going from a vague memory it looks like you might be jetted a little lean in the primaries and pretty rich in the secondary's. Off hand, I'd probably lean out the secondary's and leave the primaries alone for now. What are your cruise readings under light to medium load and maybe 2,500-2,800 RPM?
> 
> Tough call on your spark plug range because 8 is a pretty cold plug but your compression is high. On my 670's and 9.32:1 compression I run 6 on the NGK plugs. While your 10:1 compression seems like it calls for a little cooler plug, the physical results sure look like you should go a couple numbers hotter. Wallace Racing has a great sparkplug reading tech page: Wallace Racing plug reading.


Thank you.

I don't know exactly my AFR in the 2,500 to 2,800 rpm range, but just cruising in general or light acceleration is 13s and 14s. Now that our temps have cooled a little this week, I may get out and drive it some this weekend to get some more specific numbers.


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## Jim K (Nov 17, 2020)

michaelfind said:


> I appreciate all the great advice here and I'm getting closer to having things gradually jetted correctly. I'm at about 800 feet, so our elevations are pretty different. Still, I'm curious what you are running in your eddy carburetors for rods and jets.
> 
> Currently I have the following:
> front carb - primaries .100 with 7052 rods and blue springs; secondaries .083
> ...


Michael,
At my altitude I'm running 7057 rods and .083 jets in both carb primaries. Secondary jets in both are .077. Eddy recommends, and supplies .077 secondary jets for their own dual quad packages. My cruising AFR range is around 15-15.5.


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## armyadarkness (Dec 7, 2020)

michaelfind said:


> I appreciate all the great advice here and I'm getting closer to having things gradually jetted correctly. I'm at about 800 feet, so our elevations are pretty different. Still, I'm curious what you are running in your eddy carburetors for rods and jets.
> 
> Currently I have the following:
> front carb - primaries .100 with 7052 rods and blue springs; secondaries .083
> ...


I don't know how I missed this post, but as you know, I jet my eddy constantly. Im sure that our numbers wouldnt be the same, but the pump jet linkage hole, air flap, and needle spings, all make noticable differences in drivability. 

Don't be afraid to make your own combos with the needles and jets, regardless of what they list!

Blue springs would be used if you only has 6hg of vacuum. So if you have 10hg of vacuum, then those springs wont have enough boing to get the needles out of the primaries, but that would show up as a lean condition out of the hole and at cruise.

Are you staying rich or temporarily hitting rich? If staying, then yes, jet combos, but if it's temporary, then try reducing your pump shots by moving the linkage arm to the hole farthest away from the pivot point. Also try reducing the tension on your air flap spring. If it's too tight then you wont get enough air fast enough to match the jets.

My air valve flap spring is too light, so when I nail it, I go lean for an instant. If you need any help with it, just pm me and Ill give you my number. Ive had countless tech sessions with eddy on these carbs.


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## armyadarkness (Dec 7, 2020)

On my 800 cfm, my secondaries are .098 and my mains are .086 with .067 rods


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## michaelfind (Dec 14, 2018)

I got out and drove the GTO a little before the day got too hot. Here are my numbers:

Light acceleration and cruise hovers around 13.5, pretty steady

WOT varies from 11.8 to 12.3.

Should I step down on the secondary jets from .083 to .077?


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## PontiacJim (Dec 29, 2012)

michaelfind said:


> I got out and drove the GTO a little before the day got too hot. Here are my numbers:
> 
> Light acceleration and cruise hovers around 13.5, pretty steady
> 
> ...


My thoughts are that IF you are running on the primaries, you want to step them down as you don't cruise or use light acceleration on the secondaries. WOT looks good in my book. So focus on getting the AFR down just a tad more and closer to the 14.1-14.7 range at cruise/light throttle IF possible. If you get too lean, you can cause the engine to run hotter, so make a note of your engine temps and listen for any detonation. Better to run a little on the rich side than the lean side.


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## michaelfind (Dec 14, 2018)

PontiacJim said:


> My thoughts are that IF you are running on the primaries, you want to step them down as you don't cruise or use light acceleration on the secondaries. WOT looks good in my book. So focus on getting the AFR down just a tad more and closer to the 14.1-14.7 range at cruise/light throttle IF possible. If you get too lean, you can cause the engine to run hotter, so make a note of your engine temps and listen for any detonation. Better to run a little on the rich side than the lean side.


I left the secondary jets alone and got the primaries to where I'm cruising at 14.5 and WOT is 12.3. Still feels strong and runs cool, even in slow parade traffic. My only concern now is that after a burst at WOT then letting off the accelerator, the AFR does briefly jump to 15 before settling back to mid 14s. Is this normal? Is it a problem?


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## PontiacJim (Dec 29, 2012)

michaelfind said:


> I left the secondary jets alone and got the primaries to where I'm cruising at 14.5 and WOT is 12.3. Still feels strong and runs cool, even in slow parade traffic. My only concern now is that after a burst at WOT then letting off the accelerator, the AFR does briefly jump to 15 before settling back to mid 14s. Is this normal? Is it a problem?


Yes, probably normal. You let off the gas and you cut off the fuel so you have in a sense created a lean condition. It could also be a result of the exhaust scavenging effect as the exhaust is still pulling hard on the cylinders and there isn't a rich condition present as it was at WOT. So, I would not be too concerned. The numbers look good and what you have may be perfect for your engine build. You can also pull a plug or two and see what they look like which can give you a clue as to how the fuel mixture is running.


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