Originally Posted by
Cat 1
Thanks for the tip Bert, didn't know this. I think I can hear this happen and its as the reading drops below 1000 on my tach - sound changes like its ignition related and the idle falters a bit.
Another thing I noticed as I tend lean I can hear an odd little exhaust "popping echo" sound. Is this common and is it a lean indication. I looked back at your boxer running on you tube and don't hear it but your probably set on the curve. Listen as I lean to shut off at the end and you can hear it well.. I can get it to make this sound when running and just wonder if its a good lean indication.
I also noticed you run mufflers - What are they off of?
When Idle drops below 1000, on mine I start hearing the camgears chatter a bit.
As John said, the wet popping sound is not becaue of lean or rich, it is because the valves are timed for higher RPM, so the exhaust stays open a bit too long at idle. This causes the pressure in the exhaust to reverse when the piston starts going down but the exhaust valve is still open. A richer mixture camouflages it a bit because of the afterburning going on in the muffler or header.
The mufflers that I use are JustEngine "baffled mufflers", externally a direct copy of the original OS FS91 Surpass muffler, but they make them with a baffle, which changes the soundcharacteristics very slight but noticable. People say they can hear my engines run on gas because they sound different than glow fourstrokes, but I think it is the baffled mufflers that I use on all of them.
I think, JustEngines still makes them if you order them, but in all fairness, I think with your machining skills you can make them cheaper yourself.
You will need 90 degree knuckles though.