[Gucho]

"I think Clemens has the top career winning percentage of any righthander with 200 wins."

Bob Caruthers
Robert Lee Caruthers (Parisian Bob)
Bats Left, Throws Right
Height 5' 7", Weight 138 lb.

http://www.baseball-reference.com/c/carutbo01.shtml

[VeritatisSplendor]

OK, if you want to go back to the 19th century, then Caruthers did even better with his 218-99 percentage. So Clemens has the top career winning percentage of any righthander with more than 218 wins, still extremely impressive....

Some would say that records from before 1900 shouldn't count because the game was so different; for some records that is true, but won-lost percentage is insensitive to any changes in the game because they affect both teams equally, so I don't have a problem counting Caruthers.