Carb or ignition ?
Ok ... so the current carb is a 800 avs .
Do I need to drill the primary plate ?
I wrote
maybe increasing the
idle air bleed will help.
Adjusting the initial throttle position to be more closed is different. Could it help? Maybe. My suggestion was based only on the AFR information and
assumed the idle readings are somewhat correct.
Seem drastic for a 221/229 .513 on a 112 hyd roller cam .
That's fairly radical. Compared to stock it would not surprise me in the least that there is a fair amount of exhaust dilution and somehat cold combustion conditions at idle. That can shift a bit depending on the details and exhaust but bottom line is its not going to act like a stock engine.,
IMO 18* BTDC at idle is a reasonable ballpark for that combo. Details such as when the IV closes matter but its with 2* of where it ought to run strongest IMO.
I can get the idle set correctly so it runs around 12.8-13.5 with 15" of vacuum
What's the idle rpm this 15"Hg vacuum is obtained? Is this an automatic? If so what's the rpm and vac in gear?
Right now it will idle around 12.8 one moment then hit 16.5 the next ...
If I lean it out a little more the afr jumps to 20ish.
Sounds like the idle mix screws are highly sensative. probably remains true even if the WBO2's AFR intrpretation is not correct.
So based on this info here's an approach you could try:
Goal here is to reduce the eye watering exhaust at idle
Since the idle mix screws are sensative and the vacuum is strong the throttles may need to be opened a bit more at idle rpm. This will increase the fuel contribution from the transition slots. Then the idle mix screws should be less sensitive. Open them up until the engine is strongest in gear (least drop in rpm when placed in D).
If the idle speed is too high, take a degree out of the timing and then adjust the throttles and idle mix.
Taking a little timing out is another way to reduce the idle mix sensitivity since it will reduce the manifold vacuum.
As far as Carter Idle Air Bleeds go, see this:
Operational theory of the Carter idle restricions & air bleeds
Note:
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