My mower is a Craftsman LT2000, Model 247.288853 46" 21 HP Briggs & Stratton, Gold Series.
After I replaced the deck belt (954-04219) there is too much slack. If I engage the PTO almost ALL of the slack is taken up. There is too much slack in the idling position. I've checked the routing of the belt and it's correct, but for some reason, there isn't enough tension on the belt while idling.
Then belt should be loose when the blades are not turned on unless you have an electric clutch on the blades ( switch not lever )
V pulleys wear on the sides effectively making them smaller so after a lot of hours the correct belt will be too loose to drive the blades properly.
Replacing all of them ( including engine pulley ) is very expensive so I generally fit a belt 1/2" to 1" smaller.
You can check that the belt you have been supplied is the correct length by cross refferencing it with the gates equivalent by plugging the part number in here http://www.gates.com/all-search-tools/automotive-interchange-search-results
It will bring up a new window with the Gates number underlined.
Click on that the do the same in the next window and you will have the specifications of the OEM belt.
