Exhaust sound

Can it be that one had an air filter, not the other?

And a happy new year to all of you.

Mike

A straight-through " Burgess" style silencer (muffler) helps and as you suggest, the ignition timing does make a difference. Back in the early 70's I had a Commando which created a very crisp loud snarl on the over-run, (beautiful) . I could always tell the points needed adjustment when this sound became less pronounced, indicating the ignition wasn't spot on....Les

...Mike Pemberton built my ES2 motor. He got the valve timing spot on- and it makes that sound you mention, a sort of gasping snarl on the overrun and howl when you wring its neck, just before you change up;glorious. So, I would say it's valve timing.

Just to mention the other factor regarding exhaust sound. The actual full length of the pipe (from exhaust valve to open end) will set the fundamental resonant frequency (note). When the engine is in effect being driven with the throttle closed, the mixture becomes very weak probably too weak to fire so really there is very little explosive output from the engine into the exhaust pipe, in fact there is possibly a slight puff out and then a short suck back in. Somehow this oscillating pumping action sets a resonance that sounds even louder than when the engine is under load and blowing large amounts of exhaust gas out in one direction (although we do get a vacuum created at the end of each exhaust stroke but the exhaust gas flows mostly in one direction IE: outwards). You can feel this powerful suction going on by placing your hand near the silencer end as you rev then let the throttle return quickly, you can feel a massive suction occurring as air is slurped back into the exhaust...I believe it's this "slurping back" in the exhaust that causes the snarl on the overrun. Different overall lengths will effect the tuning and probably the intensity of the resonance and obviously the less restriction in the system the more violent the reverberation (less frictional damping) ...Les