I'm getting ready to break-in a new ST G-51. I have a Macs one-piece muffler that I plan to use with this engine. Here's the question:

Which muffler should I use during the break-in period--stock or Macs?

I got to wondering, should I use the stock muffler until the engine is properly broken-in, then switch to the Macs? Maybe it's better to start out with the muffler I plan to actually use (Macs)? Does it matter?

Thanks,
SG

Actually, as long as the muffler's properly-sized for the engine, you can use any brand/type for breakin. It's not that critical as long as the engine will run well and not overheat due to a too-restrictive muffler. If it's easier to use the Mac's, then use it.

Thanks for the info and quick response!