Carb conundrums. Pro tuners, come on in.

[67Charger]

Combo:

• Stock Magnum 5.9
• RPM Airgap Magnum Carb intake.
  
• QuickFuel Slayer 600 VS Carb

Carb settings:

• Mains: from 68 to 70's
• Secondaries: from 73's to 71's
• PV: 6.5
  
• Pump Cam: from Pink, hole1 to Orange, hole 1
• Pump adjustment: seems to have a TINY lag. may need more preload
  
• Squirter: 31
• IFR: from .031 to .028
• IAB: Primary from 78 to 84, Secondary from 37 to 43
  
• Idle screws: 3/8 turns out
• Transfer slot: "square" visible from underneath when primaries are closed

Behavior:

• Idle AFR in gear: 12:1
  • Screws will kill it if both in, but seem to have little actual effect on A/F beyond 3/8 open. Cannot get AF to 13+ at idle
• Cruise (maybe 10% throttle at 60 mph w/ 2.76's, 2000 rpm): 14:1
• Very gentle acceleration, 15 - 16:1, surging, missing
• Moderate accel: Lean spike (18:1 +) on tip-in, hesitation, sustained bog, then wakes up once the secondaries open.
• Accel hard enough to engage PV: 12:1, but not happy until secondaries open
  
• WOT: from idle will bog terrible, 10.8:1 - 12:1 after the secondaries open. It feels good past about 3000, but would probably be better if I could get it closer to 12.5 or 12.8.

I'm trying to get the idle mix screws to have an effect and be set around 1-2 turns out.
I am thinking the secondary metering plate is adding too much fuel at idle and I have tried to compensate by over-leaning the primary side, causing the lean cruise to be lean even with a fattened main jet. I may need to return the primary IFR to .031 and increase the secondary IAB's more to balance it out some. Once RPMs come up I get tons of fuel from everywhere, which is what caused me to lean out the secondaries. My tail pipe is VERY sooty. The car cruises at constant RPM at 14:1 just fine, but will NOT behave when accelerating at any rate unless in the low 12's and really likes the secondaries open.

 

[rlem1977]

I'm not trying to be a smart ***, but have you gone through the QF instructions? What kind of vacuum is the engine pulling? Are the jet sizes factory or were they replaced? How is the timing set? In case you don't have it, here a link to the QF doc.

http://documents.holley.com/hr_slayer_ss_series_instructions_rev._1.pdf

 

[67Charger]

I'm not trying to be a smart ***, but have you gone through the QF instructions? What kind of vacuum is the engine pulling? Are the jet sizes factory or were they replaced? How is the timing set? In case you don't have it, here a link to the QF doc.

http://documents.holley.com/hr_slayer_ss_series_instructions_rev._1.pdf

No offense taken. Yes, I did. I was greeted with a pig rich carb across the board. I have been removing fuel to clean it up, but as noted Most of the leaning in the lower circuits has been done on the primaries, and has caused new issues while not solving idle. I have listed the "FROM and TO sizes for all things I have changed in the specs above.

 

[67Charger]

Idle vacuum is 20". Timing was set at 16°, determined with a vacuum gauge and goes to 36° by 3000. Vacuum advance is hooked to manifold vacuum. (Lets not start that debate.)

 

[rlem1977]

I'm not familiar at all with the QF carbs. Holleys and Q-Jets I can deal with. Good luck.

 

[Xp29h]

First, I am no expert by any means. I’m still in the learning stage. I’ll always be there too I bet. But, One thing I didn’t see mentioned, were the floats. Are they where they should be?

I have a QF type. I’ve been months trying to lean out. May have just got it. Still testing due to weather. But I’ve gone through all you mentioned. Squirters, cams, acc pumps, air bleeds on top and even drilling holes to add more air in butterflies.

I’d go make sure power valve is good with your vacuum. Also, set your air idle screws with vacuum gauge. That is really best way. Then go back through 1 thing at a time. That takes more time, but when you fix it, you know what it was that did it.

Good luck. Hope I helped a little.. I’m sure more will chime in..

 

[lewtot184]

i think the idle air bleed (IAB?) is way too big. this will make the mixture screws do nothing. use a 218 white pump cam. you don't mention fuel pressure.

 

[67Charger]

First, I am no expert by any means. I’m still in the learning stage. I’ll always be there too I bet. But, One thing I didn’t see mentioned, were the floats. Are they where they should be?

I have a QF type. I’ve been months trying to lean out. May have just got it. Still testing due to weather. But I’ve gone through all you mentioned. Squirters, cams, acc pumps, air bleeds on top and even drilling holes to add more air in butterflies.

I’d go make sure power valve is good with your vacuum. Also, set your air idle screws with vacuum gauge. That is really best way. Then go back through 1 thing at a time. That takes more time, but when you fix it, you know what it was that did it.

Good luck. Hope I helped a little.. I’m sure more will chime in..

Floats are set to have the fuel 1/3 up the window. I may grab an 8.5 PV with some smaller PVCR's to try out.

Set idle screws to max vacuum, like timing? I started there, but then moved to leaning it towards 13.5:1 out via the wideband, but couldn't get leaner than 12:1.

 

[67Charger]

The larger IAB was an attempt to take response out of the idle circuit fuel supply to get the screws to respond (demanding more turns open on the screws to get the same amount of fuel). Anything over 3/8 out is all just too rich per the indicated AFR.