HOME GENERATOR - Muffler Defective

[drcampbell]

... Maybe a muffler off a motor home generator (Onan)

That's a good suggestion. Need not be Onan-specific.
Or an oval muffler for a permanently-installed residential standby generator.
Try to find one whose inlet & outlet diameters are similar to the diameter of the engine's exhaust port.

... determine if the difference in back pressure hurts my engines. ...

It will not harm an engine. Reducing back pressure might make the air-fuel ratio too lean if the carburettor is a simple, primitive design that doesn't have much dynamic range.

 

[hillbilly1]

Growing up our Gravely mowers had mufflers like this. I think the pipe was about 1" (YMMV). Muffler was replaceable (although we still wore Dad's shooting earmuffs while mowing). I think the connection is standard plumbing threads (maybe). You don't want to add excess weight where none is expected! So be careful!

View attachment 2567430

I put a tee in with two mufflers, no noticeable difference, block was already threaded, the weight of the two mufflers eventually broke loose from block and destroyed the threads. That was about 40 years ago.

 

[Joethemechanic]

I put a tee in with two mufflers, no noticeable difference, block was already threaded, the weight of the two mufflers eventually broke loose from block and destroyed the threads. That was about 40 years ago.

Yeah that exhaust just hanging off the exhaust port is a cantilever, so it has a natural frequency. Engine vibration has a frequency also. At times the two can come together and break chit really fast