First, I use a drop spreader rather than a rotary spreader since I
don't want the herbicide to hit the plantings bordering the yard.

So here is my paradox.
The Scott's weed & feed says to wet the lawn before using (presumably
so the herbicide granules can stick to the weeds better). However,
when I wet the lawn, some wet grass inevitably ends up running against
the drop-feeder slit which causes the fertilizer to cake-up and clog
the slots.

In summary:
1. If I don't wet the lawn first, then it spreads but it doesn't stick
to the weeds, so the herbicide doesn't work
2. If I wet first, then the drop spreader slits clog and I get neither
fertilizer nor herbicide action (or I end up opening the slits
wider by some random amount and get a random, uneven coverage)

So, what am I doing wrong and what should I be doing?