Im running a mighty demon blow through carb, and at light accel ( 1/4 throttle) my afr is only around 13.5. WOT is also 13.5. Yikes. Tomorrow I'm going to bring up the secondaries 4 sizes. The primaries I brought up from 79 to 81.

Power valve is a 6.5, vacuum is 11. Runs smooth though, a little hiccup when I when rev hard in park, so I'll have to get bigger squirters I guess.

 

I have the same blow through Demon. Vent tube extensions and HSAB size reduction richened up mine upstairs. What carb hat are you running?

 

Extreme velocity. This is my first carb with HSAB's. I think I'm a bit away from fine tuning at a 13.5 afr.

 

Do you have the down leg or annular boosters? I jetted up alot with no success, but the HSAB change and vent tube extensions made a big difference. The HSABs have a big effect on the fuel curve and aren't just for fine tuning.

 

Remember that at 1/4 throttle a fair bit of the fuel being supplied is still coming from the idle circuits (curb idle and off-idle transition ports). You may jet up and find your 1/4 throttle air fuel mix doesn't change very much.

Blow-through carbs aren't all the same. How much boost they are designed for can have a substantial effect on the A/F ratio delivered at a different boost level. One of the big changes happens to the power valve channel restriction (the amount of extra fuel metering area that comes on-line when the power valve opens). The few I've got personal experience with seem to have slightly to moderately richer jetting, a low number power valve (3.5 or so) and the PVCRs opened up anywhere from a fair bit to a ton, depending on the boost level it's calibrated for.

I offer this as being information IN ADDITION TO what was posted above, not in contradiction to it.