It sounds as if you still have some "loosening" up to do. Somewhere in the linkage path to switch positions I wouldn't be surprised to find something which does not allow "full reverse."
Gotta ask- You "retimed" before making any stitches? It may have been "optimized" prior to the change and produced suitable stitches in both directions. There's more that happens in reverse other than the feed dog direction. The fabric is moving in the opposite direction so the loop is opening in the other direction as well, inhibiting the ability of the hook to pick up the thread properly in both directions. Some machines require the timing to be "optimized" to accomplish this regardless of the "factory settings. And, we don't all read and perform maintenance procedures the same way. Test first- adjust later.
What you describe could also be a needle thing. A bent or blunted/burred needle will sometimes do "ok" in one direction, but cause problems in the opposite. The sideways needle loading in featherweights will accentuate this more than the "front to backs." What about the needle position? I assume you know but it's unbelievable how many out there don't get it right. It's really easy (apparently) to get it a bit twisted, which will produce better stitches in one direction. Then of course there's the needle/thread size thing. If not "matching" it can sometimes sew decent in one direction- not the other.
Most likely no relation at all to your problem, but feed dogs usually lose their edge in one direction only, affecting the feeding ability.
The procedures copied by Janey and/or John appear to be only Singer's suggestion for tacking the beginning of the seam. Let's face it- most of sew a short distance into the seam- reverse to tack, and sew forward again to continue on. That's three stitches on top of one another. The Featherweight ain't got enough power to layer this many lines.