Huskee 21 173cc ohc

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Previous Fixya response to similar question.
need operators Manual for my Huskee 3800 Lawn Mower

rebuild carberator

Try rotating the engine manually to check for any binding. I would also check the amp draw on the starter.

The cover does have the valves underneath. The cover is sealed with a gasket so carefully pry it off. You can fix the dents, then replace the cover sealing it with RTV sealer if you ruin the seal.
It's unlikely the starting problem is here.

check the safety switches try and jumper the one on the clutch/brake pedal first with a paper clip

go to MTD web sit follow instruction

fri-st is to check your spark, than your going need to check for compression, than go to carburetor, when you replaced your belt you may have disconnected a safety wire. try this frist let me know