A/F numbers
August 4th, 2018, 03:13 PM
#1
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Join Date: Jul 2008
Location: Santa Rosa Ca
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A/F numbers
Put on my SMI quadrajet a few days ago and just hooked up my A/F gauge. Carb is an overall much better performer than the other guys unit, idle, part throtlle and wide open all a vast improvement. I only have A/F idle numbers which are 14.2 to 14.8 at idle, the slightest turn of the mixture screws definitely shows on the gauge. Are these idle numbers good. Thanks,
August 4th, 2018, 03:32 PM
#2
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Location: Evansville, IN
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You are not really looking for good air to fuel at idle, you should look for strongest vacuum signal. Sometimes people try to get the lowest idle RPM wise they can, too. Quadrajets run down the road on your jet size, rod size, and power piston spring size, ie, the primary circuit so checking A/F at cruise down the highway will help there.
At idle, you want smoothness and "good running." At cruise, you want economy, so tune a/f there. At secondaries, you want the hammers of hell, so as big of jets as that thing will handle without bogging is usually good.
At idle, you want smoothness and "good running." At cruise, you want economy, so tune a/f there. At secondaries, you want the hammers of hell, so as big of jets as that thing will handle without bogging is usually good.
August 4th, 2018, 07:22 PM
#4
CH3NO2 LEARN IT BURN IT
Join Date: Jul 2010
Location: Land of Taxes
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14.7:1 is perfect stoichiometric AFR. 14.2 is slightly rich but very slightly. Id say you are good at that AFR. Run it for a few 100 and read the exhaust tips and plugs. That will tell you which way you need to go on the A/F adjustment.(and rods & jets for more extreme tuning which you likely don't need as it was just blueprinted?).
Adjust the timing while it's running to achieve the highest vac reading. Then go at the A/F screws and back in forth to obtain the highest manifold vac reading
Adjust the timing while it's running to achieve the highest vac reading. Then go at the A/F screws and back in forth to obtain the highest manifold vac reading
Last edited by droldsmorland; August 4th, 2018 at 07:28 PM.
August 7th, 2018, 09:04 AM
#5
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Join Date: Jan 2010
Location: central Indiana
Posts: 5,246
Give the engine what it wants, not what you think it needs. Slightly rich is no big deal, you have a little wiggle room so the engine isn’t lean on days with “perfect air”. Slightly rich isn’t black smoke and watering eyes btw!
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