Small Engines (Lawn Mowers, etc.): lack of power, doug kauffman, briggs and stratton

Question
The engine seems fine on my father-in law's (now deceased) 10hp Briggs and Stratton Craftsman mower. it's the smallest lawn tractor they sold in the early 90's. the problem is that there is a loss of power when under load, for example, I can only go in 1st gear uphill can use 2nd on level ground. is the clutch going out? can it be adjusted. would it be expensive to fix?  Thank You
Doug Kauffman
ps. I am not in a position to look up model number at this momnet, I do apologize!

Answer
You need to determine if something is slipping or the engine is down on power.  If the engine is down on power, you should also notice that the engine bogs down when cutting grass.  If the drive is slipping, you may be able to adjust the drive belt to have more tension or the belt itself may need to be replaced.  It could also be the drive belt has oil or grease on it causing it to slip.  At any rate, the drive belt from the engine to the transmission should be good and tight when the clutch is out and everything should be clean and dry.  Hope this helps.