Joined: Jan 2009
Posts: 43,982
Likes: 6,170
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
It's not too long, but it is probably too short.
It may also help to rotate the derailleur slightly clockwise, using the limit screw above the two regular travel-limit screws.