Small Engines (Lawn Mowers, etc.): replacing the piston rings in a older ariens snowblower, ariens snowblower, piston rings

Question
I have an older ariens 2-stage snowblower with a 4 cycle 2.7HP engine on it and when i did a compression test it read 75 PSI and I was told it should at lest 90 PSI so does that mean the piston rings are bad? If so how hard are they to replace and what kind of tools do i need to do it? Is it something that i can do or do i need to take it in? If so how much would it cost? The parts are around 15-16 dollars so I was wondeing is replacing the rings something that I can do? I also had the carb rebuilt cause it was leaking gas. It ran fine before but now the speed goes up and down it will speed up then slow down backfire and then do it all over again this thing is from the 70s I adjusted the carb the way he told me but the carb still leaks. Is lack of compression the reason its doing this and if so is the engine to far gone to try to fix.

Answer
 Hello Kevin:

 Before you think About Rebuilding this Engine, you need to Reseat the Valves. Most times this is the cause for loos of Compression. If after Reseating the Valves you still have Low Compression then a Overhaul is required.  Hope this Helps.

 Good Luck

 Respectfully

 John