I'm working on a 9 speed Mirage/Veloce drivetrain that has problems shifting from 1st to 2nd cog and 3rd to 4th cog on the cassette. It worked fine for about 800 miles before the problem appeared. Shifts fine in all other gear combinations.
Chain wear is way less than .75%.
Chain length has been measured large chainring to large cog + 1 link.
Can't find any stiff links.
Cassette cogs are barely worn.
Derailleur hanger appears aligned (never crashed or dropped).
As a test, I completely removed the B tension screw to ensure the upper wheel is as close to the small cogs as possible. Still no go.
Replaced the RD cable and lengthened the rear cable housing a bit (it was tight, but worked fine for 800 miles and for previous owner).
I spend nearly 4 hours 'repairing' the right shifter. New index spring carrier, ratchet bushing, and index "g" springs. Nearly lost it trying to get the spring coil bushing to seat (this took 3.5 hours).
The index spring carrier was cracked, so I thought for sure it would solve the problem. Wrong. All other mechanicals appeared in good shape. The shifters probably have less than 1500 miles total on them.
Could it be the rear derailleur itself? I'm thinking it's still in the shifter - it's just not pulling enough cable from cogs 1-2 and 3-4.