Technical Dual Quad Gods please help!! Cant burn rubber!

Hi all! finally registered for the HAMB, have lurked and fixed most of the issues I encounter just through searching, however totally stumped on this one!

Helping out a good friend with his SBC powered 37 ford and just cannot seem to get the dual quads to run right. Using a wideband O2 gauge and no matter what we try, it goes pig rich at WOT and blubbers until roughly 3k RPM and hits the desired 11.5-12 AFR. It just flatlines the gauge at 10 afr (suspect its lower than that but that's as low as the gauge reads). I will try to list as many details as possible in hopes that some one spots the smoking gun issue. I have also called edelbrock tech line, which was essentially zero help. Also tried a few reputable carb shops in hopes of some direction and most are not interested in conversing about "edeljunk" carbs heh.

Anyway set up is as follows:
GM performance aluminum headed 350, alleged 383 HP (gm numbers)
Edelbrock Dual 500 AVS carbs on top of the eddy RPM air gap manifold
Timing is an MSD billet distributor at 18 initial, all in around 3200 RPM- Vac advance attached to manifold vac.
Throttle linkage is progressive but have tried 1:1 with no improvement
Turbo 350 trans
Was told its a 3.50 rear gear but feels a little taller by the seat of the pants, might just be the pig richness however.
Operating in socal at about 10' above sea level.

Cruise AFR, idle and part throttle are all pretty much on the money, just when you go WOT it refuses to burn out, and loads up big time.

We have gone a few steps leaner on front and rear metering rods as well as primary and secondary jets.
also tried softer springs to hold the rods in the leaner position for a little longer. Tried adjusting the spring on the secondary air doors stiffer to open later and vice versa. Tried the different ACC pump holes including disconnecting the front entirely to see if it makes any change. NONE MADE A SIGNIFICANT DENT IN THE ULTRA FAT AFR. The frustration is mounting and I am fresh out of ideas. Is it just the nature of the beast?

Please help! Thanks!

 

You need to buy 2 Edelbrock tuning kits and start by reading the instructions very carefully.
You need to lean out your off idle settings.
KK

 

I am guessing, your losing too much vacuum. are you running progressive linkage?

 

Thoughts......I've seen low voltage at the coil/dist. cause a similar condition.

 

Have tried both progressive linkage and 1:1, both were excessively rich. And as for the tuning kits and instructions have tried multiple tuning guides including Edelbrock’s and ordered extra rods and jets to go along with the tuning kit we already have. Can’t figure out how to lean the off idle.

 

>>>Turbo 350 trans>>>

So burning rubber with this setup is expected by jack-rabbitting WOT on 2x4s? Jack E/NJ

 

might or might not be related...you don't know for sure what the rear end ratio is (you could jack up the car and count turns to make sure), do you have any idea what the stall speed is? what does it have for a cam?

 

If you're holding anything over about 1500 rpm in first or second gear and you stomp it and it doesn't blow the tires off ,( and goes rich) , I'd say you have problem in the carbs . I don't know much about edelbrock carbs , sorry . You could try wiring the secondary air flaps shut to see what happens ......... You could disconnect the linkage on one carb ........
One change at a time

 

I am unsure of stall speed, likely just a fresh T350 with a kit. Confirmed 3.50 gears, rotated tire twice and saw about 3 1/2 rotations of the drive shaft. Sure is a dog off the line! Tires are 26”.

Cam is mild hyd roller: .474/.510 and. 208/221 @ .050. Vacuum is around 16 hg.

Pulled plug and they are black and sooty, not wet. Plugs installed are a NGK BRK6ES, could the plug be too cold and contribute to the problem?

 

What is the compression and have you tried a non-resistor plug?
The "6" on an NGK plug is relatively hot. What kind of ignition coil are you running?

 

Compression is 9.6:1 with GM fast burn aluminum heads, 62cc chambers. The coil is an MSD HVC blaster 2. Distributor is msd as well. Didn’t try plugs yet, as figured it was likely carburetion. Figure this combo should at least be able spin em from a dead stop.

 

Maybe not, with a 13 " 1400 converter.

 

That's what I was thinking. Need more gear and more converter. More compression or less carb would help too.

 

Well that would be most unfortunate. Will try to maximize performance with what he has. Thanks for the input.

 

Don't get discouraged yet! You can make this work, but it will take time. Edelbrock carbs are damn near infinitely adjustable, get the kit's, study the instructions and experiment! Go through the ignition REAL closely too, you might stumble upon something not quite right. You'll get It!

 

I have nearly the exact set up that you have in my roadster. And yeah it's a little rich but not horribly and it runs its ass off. And my 2x4 set up is on a 290 horse gm crate 350. It works great. I will look this weekend and see what jets, rods, an springs I used. I made one adjust ment with the rods and that was it. It woke that 290 horse crate motor up big time.

 

There you have it Bro! Real life experience, right there!!

 

do you have the accelerator pumps set to the slowest hole? i found on my dual quad, a vintage why-and piece, less was more as far as the accelerator pump shot.

you might also want to try ignoring the wide band once and follow whatever change, if any, makes an improvement. dual quads can be pretty bad at fuel distribution at anything less than WOT so your average reading may be misleading. is the reading steady?

 

Nailhead Jason, would be premium if you could make that happen! Be nice to stop chasing my tail on jets and rods! Thanks in advance.

And as for the accelerator pump, tried everything including disconnecting the front one entirely. I am all for ditching the wideband if we can make some headway in bottom end power and go from there. Need to put it back in my truck anyway! But as far as the reading, the gauge only goes as low as 10.0 afr and it is very stable there from about 1500rpm to about 3k rpm when it hits 11.5-12.5 and actually starts to feel healthy.

I spoke to a knowledgeable multi-carb setup shop this afternoon, and he was also stumped, however he did say the sooty plugs indicates an ignition issue vs wet plugs which would indicate a jetting problem. Not really sure what to investigate further, maybe pick up a distributor spring kit and try to get it in a little sooner? Will do some triple checking in that area as well. Thanks again for all the insight and ideas.

 

3200 is a bit high
If you can get it all in by 2500 that is what most Chevies seem to like.

When you changed the jets ,,,, Well
what were they to start ?
What did you put in ?
What was the O2 read with both or three or four changes.

If it was af 10 at WOT on with either set that does not mean the AF didn’t change . That means it didn’t change enough to get the gauge to read. You might need to make a bigger move to notice.

Sounds like you’re pretty good on everything at idle and part throttle but once the secondaries get involved with the timing not up then things go to shit.


My buddies roadster ran well enough to drive but not well enough to be fun. Couldn’t sell him on points so I stuck a China HEI and I massaged it a little with love and added some light springs. The thing scared him when he stuck his foot in it.

 

That’s the second time I have heard 2500 for all in, will investigate first thing in the morning.

As for jetting the front carb had 89 primaries and 83 secondary, swapped to 83 and 77. The rear carb had 86 and 80s, swapped to 80 and 77. Had 65/52 rods in front and rear and tried several leaner rods including a special ordered 70/57, as that had the leanest power setting we could find. Results were poor however, cruise was way too lean. I think when we gave up for the day we had 65/55s in both. Rods have made a significant difference in cruise and part throttle operation, but we are struggling with WOT up to 3k rpm, can’t get it above 10. Have tried a few other rod combos, need to reference my notes.

 

@porknbeaner any thoughts?

 

On my little 150 hp 250, the wideband reads 15.5 to 16:1 at cruise, have seen as high as 17:1 on flat ground with a tail wind, part throttle is just over 14 and wide open is 12.9 to 13.5:1. Get the cruise AF ratio pretty lean, mine really ran better once I leaned it up, it made dead stop starts quite a bit better.

Can you limit the secondary throttle blades? or even unhook them? If you can get it running right on the primary, you will have better luck getting the secondaries to work.

 

This is how I'd probably proceed here. Of course we more seasoned guys had to learn this stuff by tinkering. What works is what you use. We didn't have A/F or EGT meters to play with.
Still say you need to know what the rest of the drivetrain is. You might be making this awfully hard on yourself

 

Have you tried running it on one carb at a time? It sounds to me like you've got too much carburetor for the engine at low/mid rpms. If it were mine I'd go back to the out-of-the-box carburetor settings and tweak the progressive linkage to open the second carburetor much later at a much higher rpm. I don't think the carburetors are getting the right "signals" from the engine at low/mid rpms to operate properly as they were designed.

 

We did try one at a time and the performance was significantly worse, was before the wideband however. As for linkage, seems you can only adjust when part throttle operation comes into play, WOT is the same regardless where you set it. And the only secondary adjustment is of the air door spring tension, which we have cranked up and slacked with negative results. Might be able to disconnect the secondary linkage completely though. Worth a shot.

Will give the original specs a chance too, likely can’t be worse!

 

You should post a video
And plot your timing curve.
All in at 3200 but what’s it at 1500 2000 2500 3000.
Won’t clear up till 3000 hummmm is that where your timing catches up? If it’s floundering it will be rich on a AF gauge with next to no fuel. When you go wide open throttle you’ll loose any and all advance from the vacuum.

 

I will work on a video next time I tinker with it. Earlier today we had a minute and swapped to the lighter springs in the distributor and was able to get it to 36 total at 2600 rpm. Part throttle might have improved a little bit but wide open was still trash. The timing mark is a little tricky to see so we didn’t get to plot out the whole curve, will require a little bit more time to record how much and when.

I will put the factory Edelbrock specified stuff in and take a quick video of our next test drive.

 

Im sorry if I didnt read it or read right past it. What is the cfm on each of those carbs? The carbs could just be to big for the combo

Sent from my SM-G955U using The H.A.M.B. mobile app

 

Another thought: edelbrocks don´t like a lot of fuel pressure. 5-6 psi is their maximum, if I remember correctly. Maybe you´re just flooding your carbs so badly. Did you check the fuel pressure?