I've just got 2 brand new Shimano Sora STI brifters, 2x9 speed, and having issues with the left one. Shifting without the cable is smooth, no issues. When connecting the cable to the Sora FD the secondary lever is almost completely stuck. I'm referring to the point in which the shifting should occur along with the distinctive 'click'. The lever doesn't want to go past this point. I have to push it pretty hard and then, after 2 loud 'clanks' shifting occurs. Even pulling by hand on the cable, from the brifter's side (so no cable housing involved) I can still feel the rough shifting. I sprayed the inside of the brifter with some wet chain lube but still no improvement. The main lever is working fine (I guess) but I do have to push on it firmly, I feel as if I'm pulling the cable by hand to shift the FD. Is this common with Sora brifters and will it loosen up in time? Is the Sora FD the one causing this issue? The right brifter doesn't have any issues at all and rear shifting is smooth.

I'd say if the shifter works (holding the cable, working the paddles) you have a problem with you cable, routing, tension, or how it attaches, unless you have a compatibility issue with the front mech (which you cant rule out. Try pulling the cable by hand. Does it work ok? Sora shifter should shift just fine.

Is the cable head fully seated into the shifter?

Is the front derailleur the correct type for your frame ie. top pull if the cable routing pulls from the top or bottom pull type if it pulls from the bottom bracket. One of my friends had a bike that has a little roller on the frame that the shifter cable around to pull the cable down. Also there could be issue with the screws that set the distance the fd moves.

It is hard to tell...The Sora front shifter does not micro-shift through its range, there is is only a couple of ratchet stops in it. The amount of force necessary to mover the mechanism may feel greater when holding the shifter in your hand and/or pulling the cable from the shifter as you explained as compared to how the shifter would operate with the shifter and cable properly installed due to the lower mechanical advantage your hands have in this situation.

My recommendation is to mount and tune properly then test it out. You may be surprised to find that it works good despite how it felt when playing with it prior to install. If it still feels problematic you will have ruled out that it was not due to not having it installed on the bars.

-j

Before you connected the cable to the FD. Did you click the left shifter (small lever) into its lowest position ?

Also check that the cable hasn't frayed or kinked inside the shifter.

The issue isn't with routing as far as I can tell because, as I said in my post, I held the cable by hand and could feel the rough shifting in the brifter. How can it be a compatibility issue when both the FD and the brifter are Sora 2 speed?

Yes, this is the first thing I checked.

FD is bottom pull and the routing is under the BB so I believe the FD is the correct type. Front shifting is working properly it's just the brifter that's having the issues.

Everything is mounted on the bike and I even went with the bike on a test run. Front shifting is working properly it's just the brifter that's having the issues. But I understand from what you're saying that the Sora FD (being a low-end FD) isn't that awesome to begin with. So I shouldn't expect much from it. I also suspect (having had a closer look to the bike) that I'd require an FD with a bit of a longer arm (the little arm with the cable clamping bolt) so the cable runs in a smoother line from the cable stop to the FD clamp. Is there a difference in this 'arm' length between FDs e.g. Sora vs. Tiagra vs. 105?

Have you lubricated everything? Start with WD-40 or similar penetrating oil. This includes brifter internals, cable, and FD. Also lube any cable guides and potential friction points. Follow with a heavier oil such as 3-in-One or a light motor oil. Either remove the cable, oil it, and replace it in the housing (the best way), or position the bike so that oil can run into one end of the housing (the lazy way but it usually works). Shift through the gears to distribute the oil.