Author Topic: Exhaust Rapping  (Read 744 times)

Offline Yasser

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Exhaust Rapping
« on: 14.09. 2020 16:54 »
Hello everyone.

A very close friend, owner of a BSA A10 use to rev a bit his engine and then, when the throtle is realeseda rapping sound comes out of the exhaust. I LOVE THIS SOUND!

I am a Norton owner. I have been trying to find the reason of this to make my mortorcycle sound like this.

Any advice?https://www.youtube.com/watch?v=aLyWx0gfC3k
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Offline cyclobutch

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Re: Exhaust Rapping
« Reply #1 on: 14.09. 2020 17:10 »
Looks like it might just be a straight through pipe. Mine doesn't sound like that.
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Online Greybeard

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Re: Exhaust Rapping
« Reply #2 on: 14.09. 2020 18:06 »
What is that light flashing near the plug; Is it intentional?
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Online Greybeard

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Re: Exhaust Rapping
« Reply #3 on: 14.09. 2020 18:08 »
Hello everyone.

A very close friend, owner of a BSA A10 use to rev a bit his engine and then, when the throtle is realeseda rapping sound comes out of the exhaust. I LOVE THIS SOUND!

I am a Norton owner. I have been trying to find the reason of this to make my mortorcycle sound like this.

Any advice?https://www.youtube.com/watch?v=aLyWx0gfC3k

Hi,

Sounds rather good but I don't think my neighbors would appreciate it!

Are you here to ask only that question? What Norton do you own?
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Online berger

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Re: Exhaust Rapping
« Reply #4 on: 14.09. 2020 18:58 »
advice is ask him who owns BSA why his BSA wrapps or buy BSA from owner *whistle*
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Online morris

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Re: Exhaust Rapping
« Reply #5 on: 14.09. 2020 19:17 »
Goldstar exhaust/silencers?
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Online Black Sheep

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Re: Exhaust Rapping
« Reply #6 on: 14.09. 2020 20:26 »
Sticking trumpets on the end of the exhaust pipes as he has done will produce that noise. Pretty anti-social frankly. For a decent sound, goldie pattern silencers would be a better choice if still a bit on the noisy side, as seen here on the wife's A10.
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Online berger

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Re: Exhaust Rapping
« Reply #7 on: 14.09. 2020 20:39 »
my  [ not for road use ]  ally ended reverse cones are very social , girlfriend has tea bag and sugar in mug and kettle boiled 3 minutes before I arrive . but I have been told the non supressed ignition upsets EastEnders fans *woo*
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Offline a10gf

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Re: Exhaust Rapping
« Reply #8 on: 14.09. 2020 22:04 »
Hey, that's Cuba! Get your friend to join, we want to know everything about his bike :O)
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Offline Jules

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Re: Exhaust Rapping
« Reply #9 on: 15.09. 2020 11:53 »
why on earth would you want your bike to sound like that!! The Goldie silencer gives a good solid sound, but looks a bit "big" for the bike IMO....
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Online RichardL

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Re: Exhaust Rapping
« Reply #10 on: 15.09. 2020 12:30 »
Sticking trumpets on the end of the exhaust pipes as he has done will produce that noise. Pretty anti-social frankly. For a decent sound, goldie pattern silencers would be a better choice if still a bit on the noisy side, as seen here on the wife's A10.

...and the crowd gasps on hearing, "...on the wife's A10."   *yeah* *grins*

Richard L.
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Online RichardL

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Re: Exhaust Rapping
« Reply #11 on: 15.09. 2020 12:50 »
Others, I'm certain, already knew this, but I had to.look it up:

Decel popping is caused by the detonation of unburned fuel in the exhaust pipe. This happens with high flow exhausts that allow more fresh air to be pulled into the pipe, causing the exhaust temperature to rise and detonate any unburnt fuel.

https://dynojet.zendesk.com/hc/en-us/articles/360003901474-Deceleration-popping-in-the-exhaust-

I think this means we would need to view this as a bike not sorted rather than a sign of a muscle engine.

Richard L.
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Online Greybeard

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Re: Exhaust Rapping
« Reply #12 on: 15.09. 2020 13:02 »
What is that light flashing near the plug; Is it intentional?

No ideas?
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Online groily

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Re: Exhaust Rapping
« Reply #13 on: 15.09. 2020 14:44 »
What is that light flashing near the plug; Is it intentional?

No ideas?

Think it's what is called an 'éclateur' round here GB. A spark-gap introduced into the HT lead. I've seen them on quite a few bikes, especially Motobécanes, over the years.
Some say - and we've been here before on this one! - that these things intensify the spark at the plug. I think they are dubious at best. Some say you can't start a Citroën 2CV of a damp winter's morning without introducing a secondary gap - like the old 'button' thing - and there must be evidence to support that or it wouldn't be done quite widely  . . . But I am a sceptic.

As to the funny exhaust noise, I reckon Richard is right. Am I not wrong in thinking that radical valve timing can create a somewhat similar effect? I remember being amazed watching Tractor Pulling competitions in rural New England 30+ years back, where several blown V8s were stacked on extraordinary chassis. Those engines on deceleration made some incredible sounds as unburnt hi-octane (nitrous oxide more than likely thrown in even) went off bang all over the place. The least tame bits of machinery I ever saw!
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Offline Triton Thrasher

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Re: Exhaust Rapping
« Reply #14 on: 15.09. 2020 15:09 »

I think means we would need to view this as a bike not sorted rather than a sign of a muscle engine.

Richard L.

There is always unburnt fuel in the exhaust and sufficiently high temperature near the head, to burn the fuel.  What’s usually missing is enough oxygen to support combustion in the exhaust.

A big open system can allow air back up the pipe under some conditions, such as over-run with throttle closed, so the unburnt fuel can burn. And pop like that.
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