Small Engines (Lawn Mowers, etc.): blades wont engage, briggs and straton, plastic pulley

Question
i bought a used murray riding lawn mower and i mowed the front yard the other day with it and it did fine, i shut it off to go inside and see what time it was and when i restarted the mower the lever that you push up to engage both blades would not go up. i finally pushed hard enough and it went up but the blades would not engage to cut the grass.  this mower has had the engine changed from a 14.5 h.p to a 11.5 h.p engine but like i said it mowed perfect until i shut it off. this mower has the hrdrostatic auto drive transmission on it and i noticed that when i pushed the pedal froward with my foot for the mower to go forward it hesitated for about 5 to 10 seconds before it stated to move and the same thing when you push the lever back with your foot to go in reverse.  i just looked under it and the plastic pulley in the back for the top belt on the mower had a plastic fin in between the belt and pulley and i just got through pulling it out from the belt and pulley. it is early here in the morning to see if that helped the transmssion on it. i would wake up the neighbors if i started it up. the following numbers for the mower and engne is as follows:

mower numbers:
model #:  42910x92b
serial #:  7257403641j00607 or 1257403641j00607. this mower had a piece on the back of it for a grass catcher to hook onto and it was took off and the brace has cut into the first number on the serial # and mfg date too but it it one of those numbers
mfg date is: 06043 or 96043.
like i said the brace for the grass catcher has almost took off the first number but it is one of those numbers.

the engine numbers are:
model #:  280707
typr #:  012301
code #:  9408224e
engine is a 11.5 h.p briggs and straton and this mower has a 42 inch cut.
could it be something that i ran over like a small limb or something be hung up in the mower underneath it somewhere that is stopping the blades from engageing. i have noticed the bottom drive belt that turns the blades is very, very loose. could that be causing it also.
any help you can give me on this is would appreciate. like i said everything was fine with it until i shut it off to go in the house to check on the time. there were a lot of leaves in the front yard when i mowed it but i did not see any limbs that i might have ran over and what is the best way to raise this mower up so i can look under it. can it be layed on ts side or on the back.
lanny forbis

Answer
lanny
Sounds like the blade engagement pulley may be not working what happens when you pull up on the handle the adjustment pulley gets tighter as it moves forward. Look under the mower as you pull up the handle and see if the belt is getting tighter it may have fell off.Also check the Lever Assembly, Switch. You may need to spray some WD-40 on those parts to keep from hanging up.