Re: Holley Carb Tuning with AEM A/F gauge
A few thoughts:
-Wideband A/F meters are awesome. That said, don't get hung up on a "correct number" there isn't one. Some engines want to idle at 12.5, some want to idle at 14, whatever, just figure out what the engine wants and use the O2 as a reference point for that particular situation.
For instance, finding your cruise "lean limit" would be by jetting down until you encounter a slight surge at cruise. At that point you jet up until the surge is gone. Again, this leanest cruise may be at 14:1, it may be at 16.... there are more factors than I care to list, but the main ones have to do with camshaft duration, and ignition timing at that point. This will effect your overall WOT fuel flow obviously, and the appropriate thing to do is enlarge the PVCR to bring your total fuel back into the range you require.
-I was gonna say the choke screw was probably holding open the throttle, but you already figured that out. Happens all the time and is annoying.
Opening the secondary DOES add air, but if you hit the secondary transfer slot it will add a ton of fuel. The secondaries always bleed some fuel via the .024 hole below the secondary slot. 99% of the "overly rich" idle issues I encounter have to do with transfer slot settings. This is even more critical on multicarb setups.
I like to change out the Holley flat head secondary adjuster for a 10-32, 1/2inch long set screw. This makes minor changes with an allen wrench very easy.
You need to take this effort one step at a time. Order of operation is generally:
-Secondary WOT tuning
-fix whatever stumble via accelerator pump settings. Adjusting the idle speed even a small amount can create a stumble just by loosing preload on the pump, etc. This is why I put this last, hate to fix an issue and have to revisit it.
1976 F100 390/c6
1963.5 Galaxie 446FE/c6