Is not just a matter of having a good tune pipe or muffler.
You can have a good engine, the correct muffler, good 30% fuel, the correct plug, head shimmed to the perfect clearance for plug and fuel, and IF YOU MISSED THE MIXTURE SETTING ON THE LEAN SIDE YOU WILL END UP SLOWLY DAMAGING THE BEARINGS AND THE REST OF THE ENGINE!
2 Stroke engine tunning has become easier with today's better carbs, but if you desire to extract the most out of them, you need to know how to tune to your machine specifics and HOW YOU FLY.
Heavy enphasis on HOW YOU FLY.
Example, and person who flies easy, does a few consecutive flips and flies around again can stand a leaner setting that one who really loads the head on off all the time.
Aids like Carbsmarts can help if you can set the parameters and linkage right. Newer regulated OS carbs (and old Cline Regs) also keep better constant fuel flow when demands rise. A well set YS does well too. The entire Fuel System (tubing, clunk or fuel magnet, filters, tubing) plays another important role.
The trick is to know how much on the rich side you need to tune to accomodate the most harsh load and moment YOUR engine will see in YOUR flight.
Two diferent flying style individuals with identical helicopter will need two diferent neddle settings.
The safe way to approach your optimal settings is start rich, fly the same short routine, monitor temperature, re-neddle, and repeat until the temp begins to rise or you feel the engine sags under load. Be careful, OS engines can run on the hot/lean side for a bit and not drop power while they are destroying itself. This is why temp monitoring is important. Dont ask me what temperature is a safe limit, all engines run slightly diferent depending on weather, fuel, muffler, etc.
Your engine must be able to hold virtually constant through a tank of fuel. If it does not, you have details in your fuel delivery you need to address.
Clear as mud, right?
BTW, bearings are cheap, change them as least one a season or when you see noticeable performance drop, idle is hard to maintain, or the most obvious, they get loud.