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Popping in silencer??


Howard

Well Known and Active Website User
VOC Member
Not a mixture or air leaks question !!

I've never known why Vins don't use megas, never questioned it, straight pipe always worked well for me on the track.

After trying various silencers on my roadgoing Egli a few years back I finally found a reverse cone mega (style) that let the engine run right and didn't burst my eardrums. The only problem was a funny plopping sound in the exhaust on tickover. After a few months, I took the silencer apart to discover the "mega" had a tube with baffles round it, and the "reverse cone" was just a cone. I put a tube (piece of exhaust) through the cone to the baffle tube and heypresto, plopping sound gone.
Today, I've fitted a new silencer (the old one was getting a bit scruffy) similar style but a bit shorter and the plopping tickover has returned. Looking down the silencer, the baffle tube again stops before the reverse cone.

OK, clever people, WHY??

H
 

Colin

Well Known and Active Website User
VOC Member
'cos you need something to do to keep you out of mischief If you were not Fettling (?fiddling) with your Vin you would have to do the garden or the washing up,or somesuch. Look upon it as a bonus !:rolleyes:
 

peter holmes

Well Known and Active Website User
VOC Member
Not a mixture or air leaks question !!

I've never known why Vins don't use megas, never questioned it, straight pipe always worked well for me on the track.

After trying various silencers on my roadgoing Egli a few years back I finally found a reverse cone mega (style) that let the engine run right and didn't burst my eardrums. The only problem was a funny plopping sound in the exhaust on tickover. After a few months, I took the silencer apart to discover the "mega" had a tube with baffles round it, and the "reverse cone" was just a cone. I put a tube (piece of exhaust) through the cone to the baffle tube and heypresto, plopping sound gone.
Today, I've fitted a new silencer (the old one was getting a bit scruffy) similar style but a bit shorter and the plopping tickover has returned. Looking down the silencer, the baffle tube again stops before the reverse cone.

OK, clever people, WHY??

H
Is it Popping or Plopping? all sounds a bit like toilet humour to me, could it be a rich mixture, perhaps to much vindaloo!
 

vibrac

Well Known and Active Website User
VOC Member
My guess is the reverse cone allows some air to enter the chamber immediately behind the cone where it then either plops when the next pulse of exhaust gas hits it or perhaps it plops when the relative cold air rushes in. Either way once the pipe goes to the end of the cone the chamber no longer connected to the atmosphere and the effect disappears. Incidentally I guess that also makes the reverse cone effect (If there is one on a baffled silencer) redundant. as you now just have a straight through pipe with a chamber around the baffles just like a tubular silencer
 

Howard

Well Known and Active Website User
VOC Member
Is it Popping or Plopping? all sounds a bit like toilet humour to me, could it be a rich mixture, perhaps to much vindaloo!
It's more of a plop noise than anything I've heard from an exhaust. It's not a mixture or fuel problem, the engine runs fine, it's something to do with the end cone, because putting a straight pipe through it stops the noise. I'll just have to stop letting it tick over. And it's nothing to do with unburned fuel in a hot silencer, because it does it from cold. :(
 
Last edited by a moderator:

Nulli Secundus

Well Known and Active Website User
VOC Member
VOC Forum Moderator
Most parallel twins (Tri......., BSA and Norton etc) that I have heard running on short reverse cone meggas sound dreadful, plop plopping away that is reminiscent of those slow motorised pleasure crafts you use to see at water resorts and caused by the water lapping other the exhaust outlet.

I don't think the short reverse cone would of been my first choice of silencer. Commando reverse cone silencers (peashooter) sound fine on the other hand, but too small to fit a Vincent pipe.
 

Howard

Well Known and Active Website User
VOC Member
Could this be a 'suck-back' overcoming a partial vacuum within the end of the mega?
This would makes sense. It doesn't sound like an explosion type of noise (hence "plop" not "pop"), but it could be some kind of organ pipe type sound due to air flow. I'll put up with it, it's lighter and shinyer than the last one and it makes a nice growl when it's not on tickover. :)
 

ClassicBiker

Well Known and Active Website User
VOC Member
Not a mixture or air leaks question !!

I've never known why Vins don't use megas, never questioned it, straight pipe always worked well for me on the track.

After trying various silencers on my roadgoing Egli a few years back I finally found a reverse cone mega (style) that let the engine run right and didn't burst my eardrums. The only problem was a funny plopping sound in the exhaust on tickover. After a few months, I took the silencer apart to discover the "mega" had a tube with baffles round it, and the "reverse cone" was just a cone. I put a tube (piece of exhaust) through the cone to the baffle tube and heypresto, plopping sound gone.
Today, I've fitted a new silencer (the old one was getting a bit scruffy) similar style but a bit shorter and the plopping tickover has returned. Looking down the silencer, the baffle tube again stops before the reverse cone.

OK, clever people, WHY??

H
I got a little curious about all this and "googled" "cross sections" and "cut away views" of "reverse cone" and "refraction" mufflers. I got some strange stuff pop up. In the flotsam that floated to the surface was some relevant cut away and cross sections. The majority of which matched your description. So it would appear this is normal practice and an intentional part of the design. Beyond that I couldn't find much.
Steven
 

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