That's what we do... needle spacer...
... but,.. if you're into experimenting,... (which it appears you are)
...
there is an airjet above the rubber diaphragm accessed from the top... (making it larger or smaller will change the amount of vacuum pulling at the slide)...(not sure which way does which)...
Adjustment of enrichment at full vacuum decel,.. is the TEV's job... but by playing with the spring, you are only adjusting when it activates, which will make it activate when it shouldn't...
Not sure how,.. but you need to adjust how much fuel it adds, rather than when...
I believe the TEV is not really doing much incremental fuel control... more like the vac-pet,.. it's open or closed...
...(a tapered needle, is incremental... a flat stopper, is on/off)...