I have a 2002 618 with a 52 inch front mounted mower deck that has started stalling out when I try to engage the mower deck. I removed the PTO from the deck and tried just engaging clutch and engine does not stall out. remove cover from the deck and removed main drive belt and engine continues to run fine when engaging clutch. This would seem to point to problem being with deck. Where do I start looking? Pulleys seem to have good bearings on them with very little play in them. The engine is a Briggs conversion engine I installed 6 years ago.