Weird, sudden AFR issue Proform 750cfm!
It's just weird to me that I can adjust the mixture screws to get low 13's at idle in gear ( the mixture screws are only about 3/4 turns out) , then by 10 mph it's going rich and by 20mph it's at 10.0 and stays there up to at least 50mph. I didn't drive it very far or get on it to see what it does beyond that.
The mixtrure screws just trim a portion of the idle feed. As soon as the throttles crack open, three things happen.
a) More transfer slot exposure increases making the idle port less relevant.
b) Less transfer slot is exposed to atmospheric pressure, so less air may be mixing into fuel air mix from the slot above the throttle.
c) With a hot cam, vacuum under the throttle is increasing. More vacuum will pull harder on the idle circuits. This will increase flow until somewhere around 14"Hg when it chokes. Above that, more vacuum doesn't increase fuel flow. (That's why a stock setup is easier - its always above 14"Hg so doesn't change)
Closest bit I had to check emulsion holes was .027
Dry, it barely fit, so I would say .028 is correct.
Either x 4 is way too much.
Increasing the air bleeds and e-holes can cause unpredictable results. Often increasing bleed pushes more fuel into the mains, especially at start up of flow. Only as the circuit approaches max flow does it typically reduce the proportion of fuel.
Have you read Tuner's description?
Post 2, and post 5 shows it graphicly although not extreme.
Emulsion Tuning
Idle seems happiest about 13.0 in gear at 775 rpm, hardly any rpm drop from park, maybe 50.
Sounds good.
IFR relocation.
Relocating the Holley Idle Jet
Some Bits and taps links:
Holley drill bits, etc.
Building a Proform/Qft 750
I usually use a hand held pin vise and place the set screw in a variable speed drill chuck. Go slow but steady. Some swear by nose grease. I use a little WD40 or such. The only set screws you really need to drill will be for the IFRs. The e-holes just plug two.
