Won't stay in second smallest sprocket

[huskyresqr]

My friend just bought a new bike...on the web....so he had to put it together. I'm kind of the neighborhood fix-it guy...and I used to work in a bike shop...a very, very long time ago....I helped him with the final "fine tuning"...brakes, shifters, but I can't seem to figure out why the bike shifts flawlessly except for the second (closest to the axle) sprocket of the rear cassette.

...only thing i can think of is that the sprocket is in someway damaged...or maybe I just have no clue...any help would be appreciated...

Larry

[GeorgeET]

Not much info re type bike and shifters. If its an SIS than it could be the shifter toggle itself. Also check for a bent hanger.

[huskyresqr]

it's a Motobecane Cafe Sprint DT with a Shimano Deore set

Larry

[Bill]

Also check the cog to make sure there are no obstructions in the valleys or possible a bent tooth. Like George said check your shifter.

[Joe_W]

It might also be a worn dérailleur spring, but then it'll shift ok in one direction and skip gears in the other (depending on the adjustment, you can tune only one direction the other will always be off...)