How do I adjust the drive belts on my Countax c300h mower?

if you mean the cutter belt from engine to deck then you need to find the tension release lever under the left footplate, move this lever forward to release tension.
Then looking at the right front of the machine just above the exhaust and below bottom of bonnet there is a threaded rod and a knuckle which is attached to a kind of frame which in turn attatches to the drag link on the front of the deck, release the clip from the knuckle and thread in or out as required, re fit pin, move tension lever back to check progress.
The sweeper / tractor belt is adjusted by slackening the sweeper attachment lever pivot bolts, and either depending on age of machine (old) take bolts right out and refit in next hole, or (newer) adjust by turning nuts on threaded adjuster bolts which go through the pivot bolt head, when correct tighten up all nuts / bolts.

Paul
March 2010