Craftsman Push Mower
Model: 907.388920
Serial: 112905M023952
Engine:10M902 0489 E2 05101754
Not misfiring violently like a car does, but rather a series of quiet muffled pops from the exhaust in between an otherwise perfectly running engine.
I've had the same issue before on an entirely different Briggs & Stratton engine that was a horizontal shaft. I never did find the cause of that one either.
This muffled pops syndrome seems to be much more difficult to pinpoint than your typical surging issue. A surging issue is always caused by fuel starvation.
The other day I was walking out of the VA hospital. A construction crew had a generator running there. That generator had the exact same muffled pop syndrome as my push mower is experiencing right now. The generator at the VA will be the 3rd small engine that I've encountered with this mystery issue in my lifetime.
I'm thinking it's probably unmetered air getting in somewhere. I've got the new diaphragm and tank gasket installed, along with a new primer bulb.
The gasket surface of both the tank and the carburetor are flat. I checked that with the straight edge of a steel ruler.
Everything is there where it's supposed to be except for the throttle shaft seal. Those throttle shaft seals are always made out of a light foam material and they always disintegrate in short order. I'm hoping you guys will tell me the little throttle shaft seal is more of a dust seal than an air seal.
Thoughts?