lawn mower stall after 1/2 hour working

I bought a Honda HRR 216PKA K9 series a few months ago. The mower worked perfectly well when I first bought it. However recently, the engine keeps on lacking power and stall. This lawn mower has self propel facilities. I want to know if the self propel mechanism is driven by a belt or gear. If so will the belt slips if the grasses get lodge into the pulley that drives the belt. Also is there any fuel mixture screw I can adjust the fuel mixture of this engine as I find the engine is lean on fuel and maybe this causes the engine stall. Can anyone has this problem with the same Honda Engine?



Thanks