Need Quick Fuel carb tuning assistance

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duster360

duster360

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Location
Alabama
Combo is 67 dart
340 ci
Dynoed 400hp
Timing is 20* at idle
34* total
4 speed manual trans
3.55 gear
I had a different carb a year or so ago (AED) and it didn't have quite the easy tunability as the one I have now. I never bothered much with the other carb, just got it to cruise and idle ok and left it alone. I now have a Quickfuel SS 650 DP, with all the adjustability you could want, need to start tuning. I know way more now than I did then, so things are getting easier. I have the quickfuel to where it will idle in the low 13's and cruise there as well, but the closer I get to 2700ish rpm it will start to drop on the AFR to high 12's or 13", so I know there is tuning to be done in the main circuit.
Now here is my main concern. Just say I am crusing along and have to slow down enough that I can shift into first gear (no traffic, 4 speed manual) and floor the throttle, sometimes it will gas foul a plug. Just did it an hour ago. Ran like crap on the way home, pulled up in the driveway, shut it off. 1 minute later opened the hood, started it and let it idle while checking timing and it clears up and starts idling well again. I know I can rejet the carb and restrictors, but should a BOX STOCK Quickfuel SS 650 DP do this on my combo. The Holley 4777-4 I had on it originally was awesome. Never had this issue.
My first question is, should this carb throw that much fuel to this motor to foul plugs. Engine is low milage and in great condition. I have 245/60 cooper cobras on the rear and in 1st gear can light them up at 25 mph.

Quick Fuel SS-650 SS-Series Carburetor 650CFM

Booster Down Leg
Brand Quick Fuel
CFM 650
Choke Electric
Circuit 2
Fuel Gasoline
Fuel System Carbureted
High Speed Air Bleed 31
Idle Air Bleed Size 71
Material Aluminum
Model Super Street Series
Primary Main Jet 70
Primary Power Valve 65
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Mechanical
Secondary Main Jet 76
Supercharged Application No
Throttle Bore 1-11/16 inch
 
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The old Holleys were often better tuned.
Seriously.
You can copy the bleeds and restrictions from the 4777, especially an early one.
Downleg boosters should have more signal but in reality seem to be more difficult to get a nice initiation.
But start with the 4777 and tweak from there if needed.
 
What I would do;
Reset the fuel level slightly lower, make sure the slosh-tubes are installed on the bowl-vents,and replace the 6.5 PV with a 10.5, and downjet the primaries to 68s, and
install whatever sparkplug fits your heads that matches the RN12YCs, in heat range. Those plugs IMO are fantastic; mine have over 100,000 miles on them, fired by the Big Yellow Accell square top. .
And I would work my way up to 200*F minimum coolant temp.
My idle timing is just 14*, on purpose, (different story) and I don't have an A/F gauge on my engine, (also different story). My distributor has a two-stage curve in it. It begins advancing at 900/1000 and is all in at 3400. The kink is at 2800, where the timing is 28*, all with the initial of 14*. And the Vcan ( you gotta have a Vcan with a manual trans and a 230* or less cam), is modded to provide 22*, and I bring it in as fast as it is able (aluminum heads).

I had a 340ish hp 367 with a manual trans and 3.55s. At 930ft elevation, it would initiate a second gear spin at up to 55mph with 275BFGs.
245s were a dangerous tire for me, as the car would spin out on every turn with just a tad too much throttle (ancient 750DP). I often found myself up on the median and facing backwards. The thing about manual trans cars is that the engine is directly married to the tires, and an 11/1 Scr engine has a lot of resistance to being turned (compression braking) by the tires, and 245s are just too small. So when I would take my foot off the gas in mid-turn with the steering fast approaching full-lock,( yeah I know; too hot!), the tires would simply give up and become skis, and around I would go, again. It took 295s to make cornering fun again. These tires have enough sideways rubber that by simply towing the clutch, the tires regained traction, and the car would recover. I can drive in traffic again!
Later I swapped out the 223cam for a 230, and traded away a bit of bottom end, to get a top-end rush, like the 292/108 had done.. The loss of torque at the bottom was so severe that I had to regear the back; first 3.91s then 4.30s. This eventually (another story) led to the Commando box with a 3.09 low, and a return of the 3.55s. Now it takes off like as if it had 4.10s, perfect for my combo.

Get your idle and low-speed bugged out first before moving up. The primary throttle has to near close, to get the transfer slot synchronized. Don't be afraid to give up some idle timing. Forget the idle vacuum, IMO, that means nothing........... cuz nobody drives a big-cam manual-trans engine, at idle. Well almost nobody (another story). To make 400hp with an iron headed 340 takes a lotta rpm, and so, a big cam. I'm guessing your engine should be idling at 750/800 at 10 inches or less. If it is higher and you have a 292/509/108 cam or more, then your transfer-slot sync needs work.
FYI;It is possible to drive a 292/108 cammed 367 at 550rpm in gear on flat,level, hard ground, with a nicely T-port synchronized, 50 year old 750DP, on an AG intake, with 5* of lead; oh wait, that's 360 power,lol.
Don't be afraid to take out some idle-timing. IMO you can't, or shouldn't, or I don't recommend it, run the same idle-timing on a hi-compression M/T car, that might be "normal" for an automatic; and it's no big deal to run 14ish in your combo. You can hide a lotta crap carb and distributor adjustments with a fluid coupling stalling at 2400 or more. But a combo like yours with 3.55s or less, has to be pretty close to perfect, else you will be riding the clutch all the time, at low mphs.
Happy HotRodding
 
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I have Edelbrock heads. Cam is comp cam xe275hl ( 233-237@.050 with .525 valve lift intake and exhaust.( 411hp at 5700rpm) Just this morning I set the front Tslot to .040 exposure and opened the rear butterflies to just a little under the rear Tslots (almost perfect) I started the engine got it hot (195* tstat) and have been running 1/2 turn in all four corners, I had to open them up a little over 1/8th turn. Also dropped the pump shot from 31 to 28. Idle is at 850 rpm. Just by the way it idles and blipping the throttle I think I am headed in the right direction. You are right about the timing at 20*, those cylinders are hitting hard and it wants to jump up and down in low gear when taking off if not clutched right, especially with the grabby centerforce clutch.The autolite Ar3924 spark plugs I use are the equivalent to the champion RN12YC.
 
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Like some other people said I probably throw 69s in it on the primary side check my pump shot cam then take a vac reading and see if my power valve is right.
Did you say what the air fuel mixture was at wide open throttle?
The jetting seems really close primary to secondary, to be honest, I want to see a 7-9 jet spread when running only one power valve.
 
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I also bought this newer how to book on Holley carbs. Good info in here for the beginner super tuner.

E24A1DCD-6F12-4F89-99B3-FDE9F5A1764E.jpeg
 
MOPAROFFICIAL said:
Like some other people said I probably throw 69s in it on the primary side check my pump shot cam then take a vac reading and see if my power valve is right.
Did you say what the air fuel mixture was at wide open throttle?
Click to expand...
That is something I need to look at also
 
Opinion on emulsion holes in metering blocks. Mine have 10 per block. Should I block off some of these? Or would it richer up the mixture if I do that?
 
MOPAROFFICIAL said:
It's not uncommon to run a jet size or two smaller than out of the box
Click to expand...
I remember reading in my older edition Holley carb book that double pumpers are jetted more toward racing than street cruising. I agree with your post above.
 
The #69 jet helped just a touch. May need to go #68. Forgot to video the vacuum gauge but it was between 9”-10” at idle. Third gear to the floor, let out at 5000 and AFR was at 13.1.
Video of idle coming if I can post it. Says file is too large.
 
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duster360 said:
Any opinion on the emulsion post above.
Click to expand...


If you have 5 emulsion blocks and they are all open...that's not good.

A good starting point is 1 and 3 get .026-028 bleeds and block 2,4 and 5.

If you block doesn't have brass in it, make sure you measure the holes in the block. If they are .026-.028 you can leave them. If they are bigger, use brass set screws drilled to size in the holes.
 
yellow rose said:
If you have 5 emulsion blocks and they are all open...that's not good.

A good starting point is 1 and 3 get .026-028 bleeds and block 2,4 and 5.

If you block doesn't have brass in it, make sure you measure the holes in the block. If they are .026-.028 you can leave them. If they are bigger, use brass set screws drilled to size in the holes.
Click to expand...
Yellow rose, I was thinking about the wrong carb. The one I have now has only 6 per block, but they are very large.
 
Always start with the fuel level.

Then the idle system - that includes the transition. A/J described that above.
Pump shot is only to cover the delay in response as throttle opens from nearly closed positions. Using it to cover up for incorrect idle-transition hurts performance and puts washes down the cylinder walls etc.

I was kiddin' about copying the 4777 that worked well. If you have it, put the primary block on your new carb and see how it does.
If not, then YR is giving you the basics. Two e-holes per well, one around fuel level, and the other around the PVCR level.

With my limited experience so far trying to get downlegs going, I'd put the IFRs down low, and with nothing else to go from, try a little leaner than QF out of the box, or try Tuner's recipe here: 4777-3 Need starting point recommendations

You won't (shouldn't) have the holes high in the dogleg that the OP in that thread found in his -3. Sometimes they are problematic. I just closed them up on a 650. You should not have to deal with that.
 
duster360 said:
My first question is, should this carb throw that much fuel to this motor to foul plugs.
Click to expand...
No carb should, but OOTB not that surprising to me.
Be sure its not the fuel pump. When you let up on the throttle while cruising, some of fuel pumps have a spring that's too stiff and sends the pressure over 7 psi.
That will overfill the bowls. You can guess how I learned this. :rolleyes:

Second. The specs in your first post dont show the IFR. Everything else being equal, smaller IFR will usually get noticibly leaner idle and engine braking.
71 IAB is on the smaller side. Changing IAB is more of the fine tune compared to changes in IFR. Larger IAB usually will lean out the idle circuit - more noticibly on the top. Say you made a big jump to 78 IABs. Then I would expect to experience stalling as you add throttle to go up a hill at 25 - 30 mph, maybe 2000 rpm. Expect is the key word. Sometimes changes don't go the direction we expect. We're dealing with fluid dynamics. Bleed in too much air, or change the mixture velocity from laminar to turbulent flow and suddenly relationships seem wacky.

As far as IFRs high or low. I generally like low but feel free to stay with high unless you have a problem that seems to be inconsistant.
Thinking more about it more, with the downlegs, the big thing may be not to bleed in too much air too early. If testing these I'd start with smaller top e-bleed, like .026 instead of .028"

Probably first experiment with after feeling comfortable with fuel level/pressure is primary IABs. Make that one change and no other.

Vizard is a great writer. His info is pretty good.
But be careful. If you are not careful, sometimes trying to follow him will take you down a rabbit hole.
shock-gif.gif

Mine was a long and somewhat expensive journey.
Eventually I learned what was real, what was applicable to the situations/carbs I was working with, and therefore my mistakes were a part of learning.
drivin-gif.gif

But it all started with trying to do some of the things suggested in Vizard's How to Build Horsepower V2
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duster360 said:
the closer I get to 2700ish rpm it will start to drop on the AFR to high 12's or 13",
Click to expand...
This is upside down. Should be leaner.
It's right in the area where things are transitioning off primary idle circuit and the mains are starting to dominate fuel supplied to the engine.
If the primary block has three e-holes and they are around .026" then they are a possibly culprit, or one of the culprits.
 
Very good info mattix. I will think on this info and apply it to my carb. That link you posted has tons of good info also. I will read through it when I can today and later tonight. Good links in that other thread also. I have a lot of good reading material now. Thanks
 
Mattax said:
This is upside down. Should be leaner.
It's right in the area where things are transitioning off primary idle circuit and the mains are starting to dominate fuel supplied to the engine.
If the primary block has three e-holes and they are around .026" then they are a possibly culprit, or one of the culprits.
Click to expand...
This is the style block I have.
34-8qft.jpg


  • Adjustable idle feed restrictions - 0.031"
  • Adjustable power valve channel restriction - 0.053"
  • 3 pre-drilled emulsion channels
  • Non-stick gaskets
  • Exclusive QFT positive retaining vent baffle
  • Stainless steel idle mixture screws with nylon seals.
  • Detailed installation instruction sheet
  • Requires QFT 6-32 thread bleeds for modification
 
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Here is some video of what I am dealing with. This is a starting point.

 
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duster360 said:
This is the style block I have.
View attachment 1715378560

  • Adjustable idle feed restrictions - 0.031"
  • Adjustable power valve channel restriction - 0.053"
  • 3 pre-drilled emulsion channels
  • Non-stick gaskets
  • Exclusive QFT positive retaining vent baffle
  • Stainless steel idle mixture screws with nylon seals.
  • Detailed installation instruction sheet
  • Requires QFT 6-32 thread bleeds for modification
Click to expand...
Looks good.

Vids I aren't working on click.
???
 
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