TRUE BUT YA GOTTA ADMIT GUTTING AND PIPING STOCK MUFFS IS PRETTY MUCH TRIAL AND ERROR. AT LEAST THE SINGLE 7/16 OUTLET STATEMENT IS CONFIRMED. YOU MENTIONED TIMING EARLIER. DID YOU KNOW MOST RYOBI FLYWHEELS HAVE 2 KEY WAYS. NOT SURE IF THEY ARE ALL INITITALLY INSTALLED WITH MORE ADVANCE OR LESS BUT IT'S SOMETHING TO CHECK. HOMEYS CAN RUN WITH NO WOODRUF KEY. USE JB WELD OR LOCKTIGHT. TIGHTEN WELL AND THE FLYWHEEL WILL STAY PUT ON THE TAPER. NOT SURE IT'S BEEN TRIED ON RYOBI BUT THE WORST THAT CAN HAPPEN IS SLIP AND THE ENGINE WILL QUIT FROM RETARDED IGNITION.??IF SOME IS GOOD MORE IS BETTER AND TOO MUCH IS ENOUGH

Except for tuned pipe applications, I personally think the whole "needs backpressure" thing is a fallacy. I use two 1/2" inside diameter tubes on the 25/30cc engines. I bought a muffler that had slightly smaller outlet tubes and in a comparison to one of my mufflers the engine lost 200 rpms with the smaller tubes....

We are talking about regular spark ignition engines here. A glow engine will often idle better with a little muffler backpressure, as it helps keep the glow plug warm/lit at idle speeds.

AV8TOR