Tunnel ram carb tuning

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66Valiant528

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So I finally installed the wide band O2 sensor in my Roadrunner. As expected fat low, lean high. Two Holley 1850-3 with seco daries tied together. I have added Quick Fuel .entering plates on the secondary side so I can change jets. Stock 134-9 which is jetted at 64 according to my QF chart. I have jetted the primaries down to 64 (from 66) with almost no change. I have ordered 60s to try and will modify the PVCR circuit later to jet back up for power. My question is after everything I've read here and elsewhere, I think that I'm going to end up running a much smaller primary jet. I've jetted single quads and can usually see changes in my 02 sensor immediately. Is it because I have 2 carbs now that I seem to need to jet so much? Any experience? See a lot of Edelbrock stuff and double pumper stuff. This is a heavy street car. 68 Roadrunner 440 Mopar aluminum 452 heads 520/540 solid comp. Msd pro billet no vacuum advance. 4 speed 4.10 gears 28 inch 275/60R15 (28 inch) useless tires that just slip through first and second. Car weighs 3970 with me in it. I'm just wondering if it's normal to drop so much jet. Jetting for part throttle cruise A/F ratio. Currently 12.3 to 1 slightly more throttle opening(accelerating not maintaining speed) leans up to 14. Super vaccuum signal. 21 inches @ cruise 15 at idle! Wow. Car runs great but pipes are sooty. Any experience anyone?
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Well I've jetted down to 57s in the front still 12 to 1. Ordered a set of QF 450 tunnel ram carbs.....
 
Sounds to me that if you reduce your primary jets and it has no effect on AFR at part throttle cruise then it’s still in the idle/transition circuit and not on the mains yet. I would look to the IFR’s and possibly mixture adjustment. Just my .02
 
I have a few things to add from experience.. the first thing is the O2 sensor isn't the end all it's just like a dino it's a measuring stick... Definitely your plugs are the end all...
Second thing is I always thought I would adjust the carburetors both identical which seem to make sense but that's not true.... Secondaries sure but primaries might be a little different that's okay...
Third yes you may have to take a large swing at the Jets as these are getting half the signal they should be getting because they were probably built to run singular... A factory dual quad setup or a setup bot to run dual quads and generally jetted for such...
Without question right everything down then what the change did or didn't do.
And last but not least have patience because you're going to have to warm up the car at least a dozen times or more and take test runs till it comes right and it's going to take time... And several jet changes and adjustments...
 
I have jetted down from 66s to 60s to 57s with no change. I am definately running on the transition slot . Idle mix is 3/4 of a turn out. 15 to 1. 1850s so no replacement bleeds. However, quick fuel blocks with 3 #28 emulsion jets, 33 idle jet and like a fat 53 pvcr jet. I have co sidereal pulling them all apart again and drilling for replacement bleeds on the main body and putting in a .071 restriction in the transfer slot passage. Most people have said dont do that work with the air bleeds. I have given up and purchased the 2 tunnel ram carbs. This is strictly a street car. I may do these modifications over the winter. I also have a set of 660s which I may throw on IF I do go to the track,but that is unlikely. Valiant goes to the track. I will let you all know how the twin vac secondary quick fuel carbs treat Mr on the street. Should be here any day now.
 
Oh and I can't believe how different the A/F ratio is between cold and hot. Huge!
 
Well I've jetted down to 57s in the front still 12 to 1. Ordered a set of QF 450 tunnel ram carbs.....


You went backwards. If you had 3 emulsion holes you should have blocked at least one of them (talking about the 600’s) and probably two of them. You need to clean up the idle circuit first, and unhook the O2 sensor. It will lie to you and I suspect it is lying to you.
 
I have jetted down from 66s to 60s to 57s with no change. I am definately running on the transition slot . Idle mix is 3/4 of a turn out. 15 to 1. 1850s so no replacement bleeds. However, quick fuel blocks with 3 #28 emulsion jets, 33 idle jet and like a fat 53 pvcr jet. I have co sidereal pulling them all apart again and drilling for replacement bleeds on the main body and putting in a .071 restriction in the transfer slot passage. Most people have said dont do that work with the air bleeds. I have given up and purchased the 2 tunnel ram carbs. This is strictly a street car. I may do these modifications over the winter. I also have a set of 660s which I may throw on IF I do go to the track,but that is unlikely. Valiant goes to the track. I will let you all know how the twin vac secondary quick fuel carbs treat Mr on the street. Should be here any day now.
Witch carbs did you get??..
 
Quick Fuel SL-450-VSTRF and SL-450-VS TRR. vac secondaries. Different front and rear carbs. Jetted 1 number diff on the primary side of the rear electric choke carb. They have all the bleeds inside and outside replaceable. As well as pvcr. And I haven't given up on my 600s. I will drill and tap everything and that includes putting a restri ction in the transfer slot passage.
 
So I installed the Quick Fuel 450s. So far it's everything I wanted. Cruise is a little lean at 15 to 15.5 to 1. Idle is 14 to 1 and carbs are very responsive. 3 floats had to be lowered and the of coarse the idle mixture screws. I may have to jet up a little. Didn't take it on the highway yet. Havent adjusted the secondary yet. Great carbs so far!

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Im heading down the same path as you did in trying to setup 2, 600 holleys. I will follow this tread and see where you end up. Where did you buy your new carbs and what part numbers are they?
Rod
 
Im heading down the same path as you did in trying to setup 2, 600 holleys. I will follow this tread and see where you end up. Where did you buy your new carbs and what part numbers are they?
Rod
I bought them through Holley. Quick Fuel tunnel ram carbs 450 cfm vaccuum secondaries. My air fuel ratio is pretty dn close. May be a little lean so I may jet up a single jet size front and rear carb. 440 282 Solid cam 410 gears 4 spd. Way better than I could get those 600s to cruise a/f ratio.. they have replaceable bleeds everywhere and a secondary plate that takes jets and the screw adjust vaccuum secondary spring adjustment. Electric choke too. Plus free freight and they charged me no sales tax! Holley products are discount exempt at both Jegs and Summit!
 
By the way this is a street car. Ya it'll make a track run but only 1 or two events over the summer. Too heavy, that's what my Valiant is for.
 
Well my mistake. Primary metering block only has replaceable pvcr and I believe MAB? Pvcr is 38 didn't look at the other bleed yet. Quick Fuel told that the rest was all threaded.

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I have there billet metering blocks on my 600s but couldn't get the cruise a/f ratio right. And jetted down to 57s (600) too lean. Jetting up on the 450s now.the front carb has 55s the rear carb 56s.

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I have there billet metering blocks on my 600s but couldn't get the cruise a/f ratio right. And jetted down to 57s (600) too lean. Jetting up on the 450s now.the front carb has 55s the rear carb 56s.

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Are all three of those emulsion holes open on this block? If so, you should have blocked the middle hole off to lean it out some, and if that wasn’t enough you could have blocked off the middle and bottom holes. That would have leaned it out.
 
Are all three of those emulsion holes open on this block? If so, you should have blocked the middle hole off to lean it out some, and if that wasn’t enough you could have blocked off the middle and bottom holes. That would have leaned it out.
 
It's still not too late. I plan on drilling out all the bleeds on the main body this winter. I will plug that hole and try them in the spring. Thanks
 
It's still not too late. I plan on drilling out all the bleeds on the main body this winter. I will plug that hole and try them in the spring. Thanks


So they were all open??? If so, that’s a HUGE amount of emulsion for a carb that size. I just want to be clear so I understand. All of them were open? If so, I wouldn’t be surprised. I’ve opened up some poor performing carbs that had all 5 emulsion holes open. Slobbering rich, plug fouling nasty like that.
 
Yes all the emulsion jets were 28s on the qf billet red block, fixed size 27s in the 450 block not treaded for jets.
 
Yes all the emulsion jets were 28s on the qf billet red block, fixed size 27s in the 450 block not treaded for jets.


Whew! That’s a lot of emulsion. That’s probably one reason why you couldn’t get a small enough main jet in it. If you had a tunnel ram with a couple of twin blade 1250’s on it, then you might need all that emulsion to get enough fuel to it. Emulsion is a funny thing and counter intuitive for sure.
 
I can't say I really know enough about emulsion tuning but I would think the more and larger diameters would lean it up no? Like you said counter intuitive. More air same fuel means lean. I've seen quite a few posts that say 28 is a good starting point for emulsion jetting. I was surprised to see the 450s had 27s, but it is a small cfm carb. But whatever, the air fuel ratio at cruise is 15.5 to 1. Could be the air bleeds? The 600s were fixed. Not for long. I'll get them to work, but 900 cfm may be adequate for my street car. Already ripped up the shock crossmember again. Is this a common B body thing? I know ....wrong forum.
 
I can't say I really know enough about emulsion tuning but I would think the more and larger diameters would lean it up no? Like you said counter intuitive. More air same fuel means lean. I've seen quite a few posts that say 28 is a good starting point for emulsion jetting. I was surprised to see the 450s had 27s, but it is a small cfm carb. But whatever, the air fuel ratio at cruise is 15.5 to 1. Could be the air bleeds? The 600s were fixed. Not for long. I'll get them to work, but 900 cfm may be adequate for my street car. Already ripped up the shock crossmember again. Is this a common B body thing? I know ....wrong forum.


When you add more emulsion you change the viscosity of the fluid. More air make the fuel lighter so it will pull the fuel up the well sooner. So you don’t use emulsion to change the A/F ratio, you change the emulsion to change the shape of the fuel curve. More emulsion make the fuel in the well lighter so it starts up the main well to the booster quicker, making the fuel curve richer. As an example, if you are happy with say, 3 equally spaced, equally sized emulsion holes and you have the MAB as close as you can and it’s still lean at WOT (which almost never happens on a Holley but it could) you can increase the bottom emulsion hole .005-.007 and richen the upper part of the curve up. Like I said, it’s counterintuitive.
 
So it's been a while but I'd like to share some street dual quad adjustment and tuning info.
I was not able to get my 1850 v/s carbs to not function properly. Although I wasted some time and money on billet primary blocks and secondary metering plates (with replaceable jets) .What needed to be done I believe with guidance from fellow Mopar people here, is to drill out the pressed in bleeds and tap them for a replaceable style bleed. There are issues with choke tower clearance and also thoughts on transfer slot restrictions.
I decided to purchase a set of dedicated 450cfm tunnel ram carbs through Quick Fuel. Highly adjustable and much better right out of the boxes. But still lean at cruise.
Anyway after taking the carbs apart and adjusting them (jetting,power valve) I wanted to make sure they were both set up the same. Primary throttle blade to transfer slot....anyway when set up the same engine wouldn't idle below 1500 rpm. Called QF for the 7th time and must have finally got someone who actually knew about dual quads. He suggested I set up the primary carb (rear with electric choke) with transfer slot set up as I had and back the secondary (front) carb idle screw off to close the transfer slot. Now set up the carbs as per normal (mixture screws for best vacuum reading) and then turned the idle down. Car idles at 900 warm with no run on and really screws! Choke works (minus 3 the other morning) driving to work. I think its funny people are upset about the salt treated streets. It took 40 years for the original quarters to go!
Again. The key was to treat the intake like a single quad and work the primary carb. This is a street set up btw. I hope this helps someone. I haven't given up on the 600s. Just haven't got around to it.

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Also this is probably why the primary jets on the rear carb are bigger than the ones on the secondary (front) carb. It all makes sense. To bad the instructions were just generic Quick Fuel carb ones. Maybe they've straightened that out by now as I got the carbs when they first came out.
 
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