Holley carb tuning idle and cruise afr - Team Camaro Tech
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post #1 of 4 (permalink) Old Jun 8th, 14, 03:08 PM Thread Starter
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Morgan
 
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Holley carb tuning idle and cruise afr

Carb is a 3310-1 4150 780 for my Copo, 2 corner idle, at 1 turn out its afr is 15.5 at idle, but 13.5 at lean cruise, turn the mixture screws out and the ratio stays the same. What is the effect on lean cruise to open up the idle bleeds in this situation? Floats are good, transfer slot is right on. In order to change the idle air bleeds I will have to drill them out, so no going back on these blocks.

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69 Copo 9560 ZL-1 4spd [email protected] 1.93 60ft on F70/14
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post #2 of 4 (permalink) Old Jun 8th, 14, 03:16 PM
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Tom
 
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Smile Re: Holley carb tuning idle and cruise afr

Try opening the secondaries a little more at idle. Just a suggestion !

69 Camaro -originally a LM1 car. 327, Edelbrock E-streets, hooker, DUI performance distributors, ultradyne cam, stewart, TRW etc. Vintage Air, AGR steering, Corbeau GTSII seats, 700R4 transmission, 12-bolt w/Eaton 4.11:1
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post #3 of 4 (permalink) Old Jun 8th, 14, 06:48 PM Thread Starter
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Morgan
 
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Re: Holley carb tuning idle and cruise afr

That makes a lot of sense, thanks. My other thought is to go down 2 jets in the front and then drill the pvcr if the wot gets lean.on these stock carbs, turning screws is easier than drilling.

69 Copo 9560 ZL-1 automatic [email protected], 1.95 on f70-14 polyglas F.AS.T. Race June 2016
69 Copo 9560 ZL-1 4spd [email protected] 1.93 60ft on F70/14
PSMCDR 2014
71LS6 vette [email protected] PSMCDR 2012 SOLD
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post #4 of 4 (permalink) Old Jun 9th, 14, 12:50 AM
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Steps
 
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Re: Holley carb tuning idle and cruise afr

Mixture screws ar the idle circuit.. only.
Yes at low load rpms it may have a insignificant effect on afrs.
Think of a carb as 3 separate identities, one for idle , one for cruise and one for power.

To tune in the idle circuit, one aims for the idle speed screw and mixture screw to be 2 1/2 turns out +/-1/2 turn.. this is done by adjusting the secondary butterflies open or closed.... basically increasing or decreasing the vaccuum leak around them to suit amount of fuel being supplied with the mixture screws and speed screws leaking air past the primary butterflies... set at factory.
Thu never have the sec butterflies closed against the carb bores, they will jamb , bend stuff ..not good.
For pump gas fuel A good idle AFR is about mid 15s as is cruise
Power rich , 11.5 to 12.5 with the timing curves dialed in correct

And when doing AFRs, be 100% sure every HT lead , plug is working 100% other wise u will get rich AFR readings

My Spelling is not incorrect...it is creative

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