I was going for the easy fixes,thinking you diagnosed the split reed allready,still look there first,cracked vac line and cdi if you can swap.The prior power loss and hissing though is a concern since we now know it's not a reed!The good news you wanted some 2t exp. they are easy to work on and relitivly cheap to repair.The bad news once your there you will want to upgear put in a racing crank and a bigger bore Ha! If you have all the parts it can be done in an afternoon.I,m leaning tward you lost a seal at this point,If lucky it's the base gasket if not got to split the cases.You can try to locate by eye,but leakdown test will give you results.I dont have alot of exp.here usually take to a shop for test,get diag then repair.If this is where you have to go I do have a stock piston and rings I can send your way with about 1000 kl on it,I also have a spare oversize piston rings and race.took about 3 months to get shipped,could also send,would need some reinberstment for that set.The only special tool you will need is a flywheel puller,you may have one that fits allready,if not get that and gasket set ordered now.Fingers crossed for an easy fix,Good luck!
