quick fuel 750s

[Stangman]

Well bit the bullit and ordered the quick fuel 750s from Barry. So my question is I have holley 1850s 600cfm currently on there
and was wondering if there will be a performance gain. I understand it might not be a huge gain but I was hoping for something.
I know now I will have alot more adjustability to dial it in. The car ran well with the 600s on there but I wasnt sure if the motor wanted alittle more. Anyway alittle info 485 with 10.75 survival heads out of the box low riser 2x4 intake 67 mustang fastback
c-6 with 3000 stall 4.11 with 26 inch drag radials. Best 1/8 mile time 7.13 at 95.60-- Best 1/4 mile time 11.40 at 117 but wasnt running that well although I did get some things squared away at the reunion. Would love to get a BT intake to match the heads but until they are around will have to wait. 

[Drew Pojedinec]

To make a blanket statement, less pumping losses is better.

The question is does your engine require the added airflow?  Go to the track and find out
My gut feeling is you won't see much difference unless one set of carbs was really out of whack.

[Stangman]

I understand what your saying what Im saying is some motors run great with a certain carb lets say a 650 double pumper for instance, now throw a 750 double pumper and it might pick up 10-15 horsepower. I am also thinking ahead when I get a different manifold and possibly a bigger cam. But I just thought maybe these carbs would flow differently and maybe give me alittle extra. I dont think my carbs have a problem now.

[Barry_R]

I'll bet that it will pick up....

We will see soon enough.

 

[Posi67]

A pair of QF 600's on my 390 with a stock BT Intake and I doubt I need more carb. I've been tempted try my 660's but suspect they will just kill the plugs and not go any faster. You have more Cubes although I think the Intake may negate any gains the bigger carbs would otherwise show. Like Barry said though, you'll find out soon enough.

[cjshaker]

Wouldn't a vacuum check under WOT show if he needed more carb? If it's at or near zero vacuum, would bigger carbs show an improvement?

[Stangman]

Hey posi 67 are your 600s  stock out of the box or are they set up nice to your motor, mine are right out of the box, look my car runs well no hesitations at any throttle points this is something that I have wanted to do was just hoping I would get a little performance out of it. I think it will make more of a difference when I finally get my manifold and a little bump in cam.

[Drew Pojedinec]

Wouldn't a vacuum check under WOT show if he needed more carb? If it's at or near zero vacuum, would bigger carbs show an improvement?

Is that the only indicator for a carburetor doing it's job    

[cjshaker]

Wouldn't a vacuum check under WOT show if he needed more carb? If it's at or near zero vacuum, would bigger carbs show an improvement?

Is that the only indicator for a carburetor doing it's job

I just asked a question to learn. It does indicate whether or not there's enough airflow to feed the engine, but doesn't say if there's enough fuel getting through. I'm just as interested to see if it does make a difference, but I'm also interested if anyone has an answer/explanation to my question. Do you? I think the LR manifold is holding it back, as it is. Switching to a MR 2x4, like he mentioned he wanted to do int he future, would probably show a marked difference, and then the bigger carbs would probably come more into play, but I don't have the experience to say for sure.

[Stangman]

I’m thinking the same way you are Doug. I don’t have the intake and I don’t want to take the chance now to break in another solid cam with it running fine. I believe that the motor will only pull what it can out of the carbs being they are vacuum secondaries so I was able to get these for now. There were some rumors that some manifolds might be made so I can only keep my fingers crossed. Not sure myself how to figure out the proper CFM but I think that’s what’s good about the vacuum secondaries. I could be wrong wouldn’t be the first time just ask my wife.

[Drew Pojedinec]

For sure intake swap would be great.....  I'm of the mind that carb calibration and fuel curve for a particular setup is so much more important to the overall power made than the size of the carb or the vacuum at WOT.

I think about my friend/mentor who built circle track carbs of very small size, or SS cars that run 735cfm carbs.

If Stangman was spending a huge amount of time experimenting with the calibration of his 600's to get them absolutely perfect and then upgraded to the 750's it would be a better experiment.
He says 1850's were the old carbs, I can say from personal experience that those do ok, but without some serious work you cannot get the best from them, ie jets and power valves aren't sufficient to get the most out of them.

[Posi67]

My QF 600's are just old Holley's they converted and removed the Holley name. . Came with billet base plates, a jet plate in the secondary's and I was surprised that they left the power valve in the primary side. They were seriously over jetted but other than that I haven't changed or adjusted anything on them. If I was running on the street then I probably would need to do something but at this point it's all foot to the floor stuff. That and the fact I'm no Carb Guru it's best I leave well enough alone.

I think you'll be happy with the 750's. As mentioned, the Vac secondary will make your life easy. I've never understood the need/want for Double Pumpers on the street. My know it all neighbour thinks everything should get an 850 DP no matter the engine size.   

[Barry_R]

They have moved away from the Holley center sections since then....but they also do a lot of tweaking on the emulsion and bleed side of the equation.  Its not just the airflow and enough fuel - its also about the quality of the fuel and air mix being delivered, along with the linearity of the fuel curve through the RPM band.

When carbs are on the small side they tend to roll rich due the the stronger signal as the engine pulls harder on the carb.  QFT seems to be better at jet guesses now, but they still err on the rich side - probably safer than way.

The neighbor is wrong.  Every car needs a Dominator.  Many need two of them.

[Drew Pojedinec]

but they also do a lot of tweaking on the emulsion and bleed side of the equation.  Its not just the airflow and enough fuel - its also about the quality of the fuel and air mix being delivered, along with the linearity of the fuel curve through the RPM band.

Dang it.... again Mr R said it so much better than I, your eloquence is astounding as always

The dynamic I didn't want to see was Stangman going from untuned 1850's to custom Qf 750's and go "wow, 750's are so much better than 600's!"  when the problem was the delivery the whole time.  Kinda like folks that go from worn out steering in a Galaxie to rack and pinion and insist that it's the best.... having never experienced properly built factory steering.

[Barry_R]

Definitely agree.  Folks that need to work with small carbs due to rules, checkbooks, or application can get really, really good results out of them if they work the package.  Like so many things, it looks simple on the outside and folks tend to fixate on the easy to understand numbers such as airflow ratings.  Carbs are rated at 1.5" of vacuum drop below the plates - not because it reflects any particular operating condition, but because of the limits of airflow testing equipment back in the proverbial day.  A carb rated at a particular cfm will flow more if the pressure drop across the carb is higher than the rating value - but the fuel handling calibration needs to be altered to reflect the operational situation, and may sacrifice performance at lower airflow levels (part throttle...)

[cjshaker]

A friend of mine that used to run Super Stock in a Hemi, often talked about the thousands of dollars that guys would spend having their carbs 'worked' by some pretty smart fellows, just to gain that last .001 in ET. I know carb work can get pretty involved when you get down to the nitty gritty, but us mortals mostly stick to basics. That's why I asked questions, just to gain a little knowledge, because those guys are pretty protective about what they know.

[cattleFEeder]

Stangman these guys have some, if there listed there are in stock. Just depends on your checkbooks pain level. Good luck Dan
http://www.cobranda.com/39duqumeriin.html

[Falcon67]

Depending on the engine configuration, it may make some difference - or not.  I have run a 650DP against a tuned 750 VS that flowed more like 840 - no difference in MPH or ET.  YMMV as they say.  Generally with a VS you are running on half the carb until you get enough air flow to make it do other things, so they have a wider range of operation than you'd expect from a similar double pumper.

[Stangman]

Thanks cattlefeeder they sold there last one last week I missed it by 5 days. The story of my life
always alittle late.

[Stangman]

Well hopefully i will get them before june 23rd, going to 1/8 mile track that weekend.
will let you guys know. Thanks for the inputs.

[Tobbemek]

If you want 2 600 1850is, .excellent performing and top tuned and to a super price, get Drew to build you a set. Heck he even tune them on his own Galaxie before he ship them out, what could possible bee better???

[Drew Pojedinec]

what could possible be better???

Doing it for free?  Tuning them at the track?  giving me a month to tinker with them instead of 2 days?   Lotsa things really could be better.....   

I'd actually be interested in Stangman sending me his old 1850's, I'll recalibrate them and send them back and he can do back to back tests with his new 750's.

[Stangman]

Drew they are those aluminum ones that you cant adjust the floats from the outside, you need to take bowl off.
Also no sights on bowls, except one that I put a regular 600 bowl on. That is one of the reasons why I wanted to
go this way. I was having a problem and I adjusted the floats alittle higher, and because I was going to the track I bumped the jets up alittle I f I remember correctly they were 64 stock and I went to 68, or they were 66 and they are at 70. I dont know how much can be done with these. 

[Drew Pojedinec]

Sounds like the 80457's, those are set really weird and often dangerously lean.  You'll certainly like the new 750's you have....

[Stangman]

there 1850s whatever that means if you look in jegs the 80457s looks like it has float adjusters, its the one with the gold in it.

[Stangman]

Went up this weekend to PA and got rained out. The carbs are on and they started right up set regulator to 6 psi and the floats were at the very top of the sight glasses so I lowered them to
The middle of glass. Seemed rich so I took out the 72 jets and put in 68s. Adjusted the idle mixtures and it idle well about 9-950 at idle and 800 in gear and smooth.When I give it gas it gets up without a bog but then at low cruise say 1500-2500 it’s not right. If I get past that it runs better and clears up.
It’s almost like at cruise you can hear in the exhaust like a thousand little misfires, almost like maybe a lean miss. At the track being I know the owner when I got there the day before on Saturday I took my nephew down the unprepped track and obviously even after a burnout had no traction but it got up and went with no hesitation, but without traction the car didn’t have a load on it so I don’t know if that is a good test. Any ideas what I should be looking for. I didn’t have this with the 600s. They have the same 6.5 power valves as each other, although the Quick fuels have adjustable everything. I’m not bad with carbs as far as floats, jetting, mixtures but all these adjustable bleeds and stuff are above my pay grade

[Falcon67]

Light throttle cruise misfire - lean primary.  Put the 72s back in, or at least go up two steps to 70s.  If it seems "fat" at idle - two things:  1) it's lean, not fat (the smell is unburned fuel) and 2) jets don't do anything for idle.  Each jet change is more or less 3% fuel, so you took 3x4=maybe as much as 12% of primary fuel out of it.  That is a LOT.

[Stangman]

I am off for a week starting on Monday so I can do a lot to the carbs. Ya know it’s my fault
I shouldn’t have changed jets before driving it. The car was in the trailer. Another thing that is bothering me about the carbs is one of them had an imperfection on the part that the gaskets seals around the fuel inlet, I used some 1500 sandpaper to get it out but before I saw it I kept snugging up the banjo bolt it was bothering me that I had to make it that tight now I’m leary about taking it off and on. But I will start from scratch. Thanks Falcon 67

[Tobbemek]

First MJ is more depending of venturi size than engine, look up what a Holley 4779 list nr: is in jetting ore QF listing inkl, PWR. and start from there. IFR is a more depending on intake vacuum and throttle bore size and if you have tho carbs you have to get them smaller ( intake vacuum sucking from twice as much fuel jettings on idle and part throttle ).
The right presidier is to go stupid lean on every circuit and bring it back up in jetting running good, except WOT that always should bee in 12.5 to 13 AF/R ratio.  One can never hurt a engine on light load looking fore the right tuning remember that, you will only hurt it on WOT if it is wrong jetted in the MJ curcuit. Lean part throttle function requires allot of advance timing to function properly, that's were most BILLET distributors with out vacuum can gets lost.

[Tony Fritz]

Stangman. here's my two cents worth.....I have 5 sets of carbs that I have played with over the last couple years. 1850's, modified 1850"s, Re-issued BJ-BK's, 660's and a set of Barrys QF 750's. Barrys QF 750's are more responsive and crisper. I've had them on 464's, 482's MR & HR etc....built similar to your motor. Bottom Line...IMHO you are going to like the QF 750's !!!

[Stangman]

They do feel strong after I get it past my off idle quirk. I’ll get it with the help of you guys, and if I can’t maybe I will take Drew up on his offer. But I’m gonna put them back we’re they were originally
With the 72 jets instead of the 68s and start from scratch. In the mean time if anyone has anything else I should try don’t be shy. Like I said after Friday we’ll I have a wedding on Saturday so after Saturday I will have time to play.

[Drew Pojedinec]

You should call your carb builder

[Stangman]

Hey Drew Ya know that whole transition slot thing, for some reason it doesnt work right on my car
or the rest of the setup is wrong so it doesnt work on my car. The transition slot was there it was a perfect square shape car didnt idle well, closed it off and it idles well again. Even on my 1850s the transition slot wasnt there right out of the box, car ran great, took off  carbs and put the transition slot in and no good. Closed it off and its fine. But anyway I have the sheet with all the numbers that the carb came with but Im at work now and its not in front of me. Would a speed shop have air bleeds or do I call Quick fuel or are they the same as holleys

[Drew Pojedinec]

Yes. That is why I said to close the transition slot. It can be almost barely visible.
On 2x4 setups setting the slot square makes it very rich as you said.

As far as air bleeds I dunno. I make my own.

[Stangman]

This is how they came
pump nozzle   33
boosters   45206
booster pin size  160
high speed bleeds  33
idle air bleeds  70      Secondary   33
MJ 72     Secondary   82
PWRValve  6.5
PWV Channel Res  52
Emulsion # stages   33-31-29
Kill bleed  29
Idle feed restriction  36       Secondary    39
needle and seat  110
accel pump30cc
Cam pink

I will open the slot alittle

[Stangman]

This is how they came
pump nozzle   33
boosters   45206
booster pin size  160
high speed bleeds  33
idle air bleeds  70      Secondary   33
MJ 72     Secondary   82
PWRValve  6.5
PWV Channel Res  52
Emulsion # stages   33-31-29
Kill bleed  29
Idle feed restriction  36       Secondary    39
needle and seat  110
accel pump30cc
Cam pink

I will open the slot alittle

[Drew Pojedinec]

You should call your carb builder

[Stangman]

Drew I do understand about the slot I have it off completely now, and you want me to open it so I can see it a smidge
correct or am I not understanding, Im not sure which are the Idle air bleeds I can look it up. Just noticing about the slot
just a smidge on the front carb and closed on the rear!? Not sure about some of the terminology but I will look it up. Dont think Im not listening Im just not familiar with doing this stuff. The basic holley stuff usually gets me by  Im new at this stuff your trying to explain

[Drew Pojedinec]

You should call your carb builder

[Stangman]

Thanks Drew I have been looking at the locations of all the idle and air bleeds, I think I’m going to need a kit. So going from number 76 idle air bleeds from 70 is going to lean it out right. You know I think it stumbles now, I have to give it more gas to get past it, or farther up in rpms. I really didn’t expect these to run so poorly it’s almost like something is wrong. As of the moment the out of the box 1850s ran better.

[Drew Pojedinec]

I don’t wanna make anyone angry bout it. But I’ve had 5 sets of custom quickfuels
Here and they were all calibrated like yours. They all ran great on a dyno. They all
Ran like yours on a real car.

Oh. Disclaimer. Set your floats to the bottom of the window first. Note changes
Make another change, let’s say emulsion, note changes.
Change the air bleed. Note changes. Please don’t change it all at once. 
You’ll get a better feel for what it’s doing and you’ll be less likely to get lost.

[Stangman]

Ok well now I gotta get them to run well, gotta go paint now see ya in a little while

[Falcon67]

Since this gets so technical    I'll start a new topic when I get my carb apart and get a recommendation on a starting point.  I think I have it pretty far off base.

[Barry_R]

Without getting into the proverbial contests...I can tell you for certain that the QFT package will have a fairly linear A/F ratio throughout the RPM band and will respond in a linear and predictable fashion to jet changes.  The traditional vintage Holley 2x4 package will be less responsive and linear to changes and will go non-linear on A/F as you stray from the OE calibrations - becoming extremely rich at WOT with even very small jets.  They drive good but you end up making significant changes to get them under control with more powerful engine combinations.

Every carb modifier and even Holley went to the emulsion happy fuel package because it flat works from a power and linear mixture perspective.  Holley's original fuel packages were equally sorted out with the emphasis on part throttle drivability and transitional behavior.  You tune to your combination and either strategy can be made to work.  Neither group did what they did because they were blind to the other issues.  The folks that started QFT and worked there were mostly former Holley employees in marketing, sales, and primarily engineering.

I concur with closing down the throttle at idle until the transfer slot is barely visible.  Sometimes they benefit from checking and recentering the blades in the throttle bores - whether Holley or QFT that seems to be missed sometimes and can give quirky behavior.  Do not close the blades all the way against the throttle bore for idle.  The blades have a 7 degree angle on them to prevent binding, but you can still raise a burr in the bore or accumulate carbon on a hard close that can lead to sticking.

You have a lot of levers and knobs to pull to adjust the light throttle burble.  Transition to main can be affected by a lot of things including specific gravity of your fuel, alcohol content, fuel pressure/float position relative to emulsions, etc.  I bet you can make it work pretty well with just a little tuning.

[Drew Pojedinec]

Yeah, in no way do wish to insult or talk bad to you Barry.
As stated, many ways to skin a cat. Being that you have some
Skin in the game I’ll happily let you walk him through getting
His purchase usable.

[Barry_R]

I think you are giving him good guidance.  Probably first step is to try them as delivered before making the jet change - then work the package from there.

[Falcon67]

Good info - why I'll request some help because the single in question here is a ProForm down leg DP body with QFT blocks.  I need to pull it apart to get the specs on the blocks.  I'll be switching to methanol later, but would like to have the gas carb at least in the ball park.  A similar unit runs on the door car, first step is to jet this one like that one - may work even though the target motor is 100+ HP over the other. 

[427LX]

If you don't have one...get a good A/F ratio reader like the AEM. This will show you where the air/fuel ratio going as you make changes on the idle/part throttle circuit. With some dual quad intake manifolds you will be able to run with a leaner cruise A/F ratio than with a single 4 bbl. intake depending on carb and engine size.
For street strip use leaning more to street...it's better to work a smaller carb a little harder than to have slower air flow thru a larger carb during part throttle.

[Barry_R]

Yeah, in no way do wish to insult or talk bad to you Barry.
As stated, many ways to skin a cat. Being that you have some
Skin in the game I’ll happily let you walk him through getting
His purchase usable.

Do not delete your original data - - it is too valuable to not have out for reference.  As you mentioned - there are a LOT of ways to skin this proverbial cat, and some comparative information can and will help as he works his way through sorting the carbs out.  The customer service side of QFT has suffered somewhat since Holley asserted control of that company, and the guy on the phone there may not be as able to approach tuning as they once were.

Also as mentioned - the very first step is to get back to the as delivered setup to establish a firm baseline - squaring up idle throttle settings and float levels are an obvious requirement, and should have been done on an air box prior to shipment.

[Stangman]

ok so I was finally able to get a look at the carbs. First thing I did was put the 72 jets in that
I took out before I even drove it. I took Drews advise and just opened the transition slot a smidge on
the back carb and just closed on the front, adjusted the floats to a smidge over a half in sight glass
and adjusted the idle mixture screws. Idle was alittle high by that time 1150 so I lowered it to 950-1000.
In gear its 850-900. Took it for a ride and it ran MUCH better, Im actually going to put 74s in and I think it will
be perfect. So the long and short of it is the problem was me. I was in a rush that day started it up and it was rich
probably because the transition slots were open alot the bowls were to the top of the sight glass I was in a trailor
which made it worse and I was getting late for work. So I jumped the gun and made some rash decisions.
I would like to thank everyone who helped me and steered me in the right direction. Even though Im not done
tuning Im in the right direction now. Again thanks guys!!! 

[Barry_R]

Good to hear that you have a workable baseline. 

As you get some driving time you will find areas in the fuel delivery that you will want to change and enhance.  The carbs have a wide enough range of adjustability that you should be able to address any issues you find.  As long as you keep good records you do not need to fear making changes - you can always "go back".  A wide band will give you hard data to use as guidance - but the old fashioned butt-o-meter will eventually win the day.  When tuning here I use O2 to get things in a safe and predictable zone - then I "feed it what it wants to eat" for power and behavior.

[Stangman]

Thanks Barry and all who replied