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Confusing carb A/F readings with 408 stroker #1506290
09/23/13 11:25 AM
09/23/13 11:25 AM
Joined: Jan 2003
Posts: 1,054
Eau Claire, WI
Charger727 Offline OP
super stock
Charger727  Offline OP
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Eau Claire, WI
I would like to switch carb on my 408 SB stoker

Has a quickfuel Q-750 double pumper

Wanted a choke and vacuum secondary for better street driving so I bought a Holley 770 ultra street avenger

I'm using a air/fuel meter to monitor things

I was surprised to see the Holey running pig-rich at cruise, like 11.7-12.0. It has 70 primary jets out of the box

I had the QF running at 13.6-13.8 (where my combo likes it at cruise) with 74 jets

I thought perhaps the power valve might have been defective, changed that, no change in the A/F ratio

I'm wondering - is the choke horn creating that much air restriction? Or is fuel getting pulled in from somewhere?

Just seems weird since a lot of people claim the Avengers are too lean out of the box...

Re: Confusing carb A/F readings with 408 stroker [Re: Charger727] #1506291
09/23/13 11:49 AM
09/23/13 11:49 AM
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert Offline
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Lincoln Nebraska
Quote:

I'm wondering - is the choke horn creating that much air restriction?


I wouldn't think so


live every 24 hour block of time like it's your last day on earth
Re: Confusing carb A/F readings with 408 stroker [Re: RapidRobert] #1506292
09/23/13 11:56 AM
09/23/13 11:56 AM
Joined: Nov 2004
Posts: 2,495
Oregon City, OR
Baxter61 Offline
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Baxter61  Offline
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Oregon City, OR
are you sure the choke was open while cruising?

Re: Confusing carb A/F readings with 408 stroker [Re: Baxter61] #1506293
09/23/13 12:06 PM
09/23/13 12:06 PM
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Columbus Ohio
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mopfried Offline
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Columbus Ohio
wrong power valve?

Re: Confusing carb A/F readings with 408 stroker [Re: Charger727] #1506294
09/23/13 12:09 PM
09/23/13 12:09 PM
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Indiana
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YO7_A66 Offline
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Indiana
""I was surprised to see the Holey running pig-rich at cruise, like 11.7-12.0. It has 70 primary jets out of the box.
I had the QF running at 13.6-13.8 (where my combo likes it at cruise) with 74 jets""

Once you know that the choke is open:
Depending on what you are calling "cruise", you may need to tune the idle/transfer circuit instead of the main circuit to fix the cruise A/F readings. Try using larger IAB's on the Holley and see if that will lean it out.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)
Re: Confusing carb A/F readings with 408 stroker [Re: Charger727] #1506295
09/23/13 03:34 PM
09/23/13 03:34 PM
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Bend,OR USA
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Cab_Burge Offline
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Bend,OR USA
Lock the choke open and see if that helps, if not then you will need to restrict the fuel feed circuit to the transition circuit Almost all Holleys are way to rich on the transition circuits You could try leaning out the idle air fuel bleeds first to see how much that will help What RPM are you calling cruise RPM? I'm almost sure all three circuits, idle, transition and main fuel circuits are working at 1200 RPM in gear and up until the secondarys start to open at light throttle pressure or the manifold vacume drops low enough to open the power valve


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Confusing carb A/F readings with 408 stroker [Re: Cab_Burge] #1506296
09/23/13 04:11 PM
09/23/13 04:11 PM
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CT
GTX MATT Offline
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My 770 had 72/75 jets out of the box


Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street
Re: Confusing carb A/F readings with 408 stroker [Re: Charger727] #1506297
09/23/13 07:19 PM
09/23/13 07:19 PM
Joined: Feb 2005
Posts: 4,309
Prospect, PA
BSB67 Offline
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Prospect, PA
Like may stated, depending on the cruise rpm you are talking about, it could be the transition/IFRs

Re: Confusing carb A/F readings with 408 stroker [Re: BSB67] #1506298
09/24/13 10:15 AM
09/24/13 10:15 AM
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Philadelphia
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radar Offline
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Philadelphia
Yo7 and Cab are right on- there are two ways to fix your problem- more air or less fuel from the transition slot at cruise. This can be attacked with bigger idle air bleeds or smaller idle feed restrictions. Either way will require turning the idle corner screws out to richen the curb idle back up to acceptable levels. On mine I ended up with them 1.5 turns out- with the fat cruise the idle screws were like 3/4 out- a good sign that the ifr/iab relationship is rich.

Re: Confusing carb A/F readings with 408 stroker [Re: radar] #1506299
09/24/13 11:17 AM
09/24/13 11:17 AM
Joined: Jan 2003
Posts: 1,054
Eau Claire, WI
Charger727 Offline OP
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Charger727  Offline OP
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Eau Claire, WI

Thanks for the suggestions guys. I'll start tinkering with it. Cruise rpm for the car is around 2700 rpm (3:55 gears) at about 60 mph.







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