I talked to the builder of these carbs and have exact numbers now: IFRs are 0.033" and main body restrictors are 0.052"
He suggested to put smaller MABs, there are 39s in the carbs. He says I have a weak booster signal problem so no fuel is drawn thru. I really dont know what to say. I think I have 32 and 34 MABs to try...
LOL…that’s why I said at the beginning you need annular boosters. I understand that’s probably not poss so you may have to do some things I try and not do because if everything’s correct you‘ll lose power. Without annular boosters we need to think differently.
As 68 HEMI pointed out above, you don’t not set your power valve opening by idle vacuum. That’s never been right and to this day, Holley and the whole internet and everyone else still teaches that.
At cruise RPM you want to see what your vacuum is and then go down two numbers as a starting point and tune from there.
For example, if you cruise at 12 inches (that would be pretty low but this is just an example) then I’d start at a 9.5 power valve. That’s 2.5 inches below cruise vacuum. So that’s a good start.
I agree with dropping the Main Air Bleed down some. It will start it on the boosters sooner and it will make it richer at WOT so you may have to reduce main jet/PVCR to your WOT back in shape.
Because you have a tunnel ram (cold air intake) and because you have a pretty big venturi and a down leg booster and because the booster is a long way from the valve you may have to run your engine coolant temperature higher than I normally would. I don’t remember your compression ratio or what you have for an ignition or timing curve, but normally I try and run between 160-170 degrees F.
Contrary to popular belief, you can run higher compression ratios on pump gas and make more power if you can keep coolant temperature in that area.
One issue when you have lower coolant temperatures like above is getting the fuel (most of it anyway) vaporized before it gets to the chamber. Of course, you can have too much vaporization and those expanded gases will displace air and drop horsepower. So it’s a balancing act.
With your induction system and down leg boosters I suspect you are having a vaporization issue. The manifold is cold and your boosters don’t atomize the fuel enough and you end up with wet (solid) fuel getting in the chambers. When you have that, it takes heat from compression to vaporize the last of the fuel and it causes a power los. Plus, you end up running more jet and most of the fuel that gets vaporized in the chamber is just wasted.
So you need the booster (emulsion adds some to this and lots of carb builders use extra emulsion to try and help but IMO that’s not the best way to do it) to atomize the fuel. Once it’s atomized then the fuel gets vaporized on its way to the chamber by manifold heat. That also pulls some heat out of the intake charges and makes power.
So you have to have atomization and then vaporization to make power and it needs to be done correctly to get the most power out of the fuel.
Soooooo…thats why you may have to run 190-195 degree F coolant temps. That will help the vaporize the fuel that wasn’t finely atomized by the booster.
I know it sounds a bit daunting to straighten this out but it’s not that bad once you get the hang of it.
If you can make your own set screws that will work.
