The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Yasser on 14.09. 2020 16:54

Title: Exhaust Rapping
Post by: Yasser 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 (https://www.youtube.com/watch?v=aLyWx0gfC3k)
Title: Re: Exhaust Rapping
Post by: Butch (cb) on 14.09. 2020 17:10
Looks like it might just be a straight through pipe. Mine doesn't sound like that.
Title: Re: Exhaust Rapping
Post by: Greybeard on 14.09. 2020 18:06
What is that light flashing near the plug; Is it intentional?
Title: Re: Exhaust Rapping
Post by: Greybeard 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 (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?
Title: Re: Exhaust Rapping
Post by: berger on 14.09. 2020 18:58
advice is ask him who owns BSA why his BSA wrapps or buy BSA from owner *whistle*
Title: Re: Exhaust Rapping
Post by: morris on 14.09. 2020 19:17
Goldstar exhaust/silencers?
Title: Re: Exhaust Rapping
Post by: Black Sheep 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.
Title: Re: Exhaust Rapping
Post by: berger 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*
Title: Re: Exhaust Rapping
Post by: a10gf on 14.09. 2020 22:04
Hey, that's Cuba! Get your friend to join, we want to know everything about his bike :O)
Title: Re: Exhaust Rapping
Post by: Jules 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....
Title: Re: Exhaust Rapping
Post by: RichardL 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.
Title: Re: Exhaust Rapping
Post by: RichardL 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.
Title: Re: Exhaust Rapping
Post by: Greybeard on 15.09. 2020 13:02
What is that light flashing near the plug; Is it intentional?

No ideas?
Title: Re: Exhaust Rapping
Post by: groily 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!
Title: Re: Exhaust Rapping
Post by: Triton Thrasher 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.
Title: Re: Exhaust Rapping
Post by: Yasser on 15.09. 2020 17:00
Hello everyone.

I really appreciate your fast and sincere anwers. In Spanish we have a say "For different tastes, different colors" maybe that's why I love this sound...

20 years ago, I was ridding a two stroke motorcycle. This sound I am describing your made me fall in love, and it was produced by a Road Rocket BSA.

Unfortunately I could never get one of this, but a Norton Dominator. And after years I also love my Norton, but my heart still love this sound.

I Cuba there is no need to care about this loud sound, if you like it you can go with it.

The red light is what we call chisperos. Have you every had a fouling plug? Try to put the high tension cable some mm far, it will make the spark stronger and maybe your plug will come back to work. Let say this is a "professional" chispero. My friend installs it just for fun.

So. After all explanations. Do you think that making an insertion at the end of the exhaust that reduces the diameter by some mm I should get more air speed in order to make the O2 reach the hot zone of the exhaust and them explode?
Title: Re: Exhaust Rapping
Post by: Greybeard on 15.09. 2020 19:29
The red light is what we call chisperos. Have you every had a fouling plug? Try to put the high tension cable some mm far, it will make the spark stronger and maybe your plug will come back to work. Let say this is a "professional" chispero. My friend installs it just for fun.
*doubt*
Title: Re: Exhaust Rapping
Post by: RDfella on 15.09. 2020 19:36
Reminiscent of the Norton 'spark intensifier'. Have one in my spares drawer.
Reminds me of many decades ago when I was working in a garage. One of our customers had 50's Bedford trucks and those models would foul plugs if left idling for any time. One of their trucks was particularly bad, so I cut all the HT leads and inserted buttons from old overalls in such fashion that the spark had to jump across the button centre. Worked a treat, but the boss was none too delighted when one day he lifted the bonnet and saw what looked like a firework display. I pointed out that it worked so he closed the bonnet and walked away.
Title: Re: Exhaust Rapping
Post by: RichardL on 15.09. 2020 22:29
So, TT, would you call it a good thing, a bad thing, or harmless fun?

Richard L.
Title: Re: Exhaust Rapping
Post by: Yasser on 16.09. 2020 15:08
No harm at all, it is useful. This is wide used on two strokes machines, where gas is contaminated with oil, lowering is combusting properties. Of course, with todays high tension coils, electronic ignition systems and platinum point spark plugs there is no need of it. So if you use a Boyer Bransden or so, forget about it....if you have an original Lucas magneto it will help for sure....

Now...

Back to the topic.

Yesterday I made my final test..

I reduced the end of the exhaust pipe...the result was a killer DB with a kind of whistling sound..SO, I started testing lengh from let say 30 inches of overall lenght until I get the rear axle and BUM....there is a point where the rapping is very loud and deep...

My conclusion..

Depending on your compresion, and cam and carb...there is a moment where unburned gasoline is trapped between the head and the first part of the exhaust pipe...the correct lenght of the pipe will make a return source of fresh oxigen reach this "dust of gas" that is actually very hot...So combustible+oxidizing+temperature BOOM, an explotion happens in the pipes and is amplified by the pipe itself.

So I am very happy with the result. Now I can ride smiling with my BSA fellow!!!

Thank you so much for your support.

All the best

P.D Triton Trasher, you nailed it!!! Thank you so much
Title: Re: Exhaust Rapping
Post by: Zander on 16.09. 2020 15:54
Can’t say I’m keen on wrapping, but each to his own.  I consider my Gold Flash to be a bit loud and reckon the pipes are straight through, so has anyone had success in repacking silencers? TIA.
Title: Re: Exhaust Rapping
Post by: mugwump on 16.09. 2020 17:21
Whers's your youthful spirit George *smile* *smile*. I have a reverse cone mega on my ariel and it sounds great.
Title: Re: Exhaust Rapping
Post by: Zander on 16.09. 2020 18:26
My 15 year old youthful spirit is still in the bottle, John *smile*
Title: Re: Exhaust Rapping
Post by: muskrat on 16.09. 2020 21:33
G'day Yasser.
I've been away for a few days.
My A10 Cafe sounds very similar. I love the sound when backing off and going down through the gears for a red light. Mine is a combination of big carbs, big valves, 357 cam and reverse cone megas. There is nothing inside from the exhaust valve to the end of the pipe.
A saying down here is "loud pipes save lives"
Cheers
Title: Re: Exhaust Rapping
Post by: Yasser on 17.09. 2020 12:04
Mr. Brown Muskrat

Can you share this sound?
Title: Re: Exhaust Rapping
Post by: groily on 17.09. 2020 16:51
"loud pipes save lives"
With you on that one Musky! . . . Even if it's a bit hard on the ears of anyone too close behind!
Like most things round here, owner included, the beast in the pic needs a bit of a clean - but the Big Black Hole is fun, and living in the sticks it doesn't upset anyone else. I'm not really an anti-social sort of barsteward, but I do like to hear where I'm going.
Title: Re: Exhaust Rapping
Post by: RichardL on 17.09. 2020 18:17
My stock silencers aren't particularly loud, but as an aging audio guy, I protect my remaining hearing when I can, so I often wear earplugs when I ride.

Richard L.
Title: Re: Exhaust Rapping
Post by: Greybeard on 17.09. 2020 18:20
I have standard looking cigar shaped replacement silencers. They have a nice sound. I don't think there is very much baffling inside. They don't have that over-run crackle though.
Title: Re: Exhaust Rapping
Post by: metalflake11 on 17.09. 2020 21:13
Only straight through will do.

Get the air in, blow it up, and get shut as soon as possible without any messing about.

They're not that loud anyway burbling about in town, and on the motorways and A roads there's no one to annoy.
Title: Re: Exhaust Rapping
Post by: Jules on 18.09. 2020 02:23
You guys sound like you need a Harley without silencers, or maybe that is your "other" bike LOL  *smile*, where I live they come "cracking" through the hills every weekend, not a good sound IMO, the standard Harley sound is good (and patented!), while the open exhaust "crack" is way too offensive.....
Title: Re: Exhaust Rapping
Post by: Black Sheep on 18.09. 2020 10:11
I live in the middle of a network of superb biking roads. I get utterly ***** off with the sounds of noisy race replicas howling around the place every sunny evening. It's a relief to hear properly silenced bikes purring past the gate. If it annoys me, what's it doing to normal people? Normal being everything from Green activists to Daily Mail readers.
We live in a world which is starting to take noise pollution seriously. Anything which pisses off the unenlightened general public is not doing motorcycling any good at all. The actions of the few can end up with us all being bannned from riding.
Title: Re: Exhaust Rapping
Post by: Butch (cb) on 18.09. 2020 12:21
But the problem being that with the emergence of day time running lamps as a requirement on all new cars that's a differentiator (sp?) that we no longer have. short of noise, next up we'll need to be experimenting with smell I suppose. 
Title: Re: Exhaust Rapping
Post by: BSA_54A10 on 18.09. 2020 12:35
I live in the middle of a network of superb biking roads. I get utterly ***** off with the sounds of noisy race replicas howling around the place every sunny evening. It's a relief to hear properly silenced bikes purring past the gate. If it annoys me, what's it doing to normal people? Normal being everything from Green activists to Daily Mail readers.
We live in a world which is starting to take noise pollution seriously. Anything which pisses off the unenlightened general public is not doing motorcycling any good at all. The actions of the few can end up with us all being bannned from riding.
What really ***** me was a really noisy Yank V twin
When the rider got to the cafe he removed his helmet, followed by the balaclava under which were ear plugs .
Title: Re: Exhaust Rapping
Post by: RichardL on 18.09. 2020 12:49
  If it annoys me, what's it doing to normal people?
[/quote]

...or sheep, for that matter.

I'm envious of you for having such roads nearby.

Richard L.
Title: Re: Exhaust Rapping
Post by: Greybeard on 18.09. 2020 14:07
  If it annoys me, what's it doing to normal people?

...or sheep, for that matter.

I'm envious of you for having such roads nearby.

Richard L.
[/quote]
The sheep in Scotland drive quad bikes
Title: Re: Exhaust Rapping
Post by: muskrat on 21.09. 2020 08:53
G'day Fellas.
Well put your ear plugs in or turn off your hearing aids. Yasser asked for it  *ex*
My first ever attempt at a video and my first post on YouTube. Only taken me all bl@@dy afternoon.
https://www.youtube.com/watch?v=ckJ5PU8CQGg
Cheers
Title: Re: Exhaust Rapping
Post by: Greybeard on 21.09. 2020 09:12
G'day Fellas.
Well put your ear plugs in or turn off your hearing aids. Yasser asked for it  *ex*
My first ever attempt at a video and my first post on YouTube. Only taken me all bl@@dy afternoon.
https://www.youtube.com/watch?v=ckJ5PU8CQGg
Cheers
Awesome!

Someone who didn't know better would think that is a much more modern motorbike.
Have you considered having disk brakes?
Title: Re: Exhaust Rapping
Post by: muskrat on 21.09. 2020 09:34
Nah, brakes only slow you down *whistle*
Cheers
Title: Re: Exhaust Rapping
Post by: KiwiGF on 21.09. 2020 12:21
G'day Fellas.
Well put your ear plugs in or turn off your hearing aids. Yasser asked for it  *ex*
My first ever attempt at a video and my first post on YouTube. Only taken me all bl@@dy afternoon.
https://www.youtube.com/watch?v=ckJ5PU8CQGg
Cheers

Seen the vid....is that an “italian warm up”?
Title: Re: Exhaust Rapping
Post by: muskrat on 21.09. 2020 12:50
Take 2, take 1 was 30 minutes earlier.
Cheers
Title: Re: Exhaust Rapping
Post by: Black Sheep on 21.09. 2020 15:32
That's one good looking and good sounding bike. Not legal on UK roads of course and wouldn't pass the noise regs for racing either. Now where do you hang the panniers and tent?
Title: Re: Exhaust Rapping
Post by: RichardL on 21.09. 2020 17:32
Yeah, Musky, I love the way that sounds and can only imagine riding an A10 with that power.  One thing, though, your's seem to sound about the same with throttle going up or down and doesn't seem to have the extra decel popping of Yasser's. From reading here, I guess that could be due to his bell-shaped pipes (not really "silencers," are they?). I think that means I don't want bell-shaped pipes/silencers, but I do like the reverse cone.

Richard L.
Title: Re: Exhaust Rapping
Post by: Greybeard on 21.09. 2020 19:42
... good sounding bike. Not legal on UK roads of course
We no longer have police in England, can't speak for Scotland. Most evenings some scrote repeatedly drives up and down our road in a car of some kind that sounds like a racing car, complete with over-run cackle. I think it's possibly a Ferrari. Why an owner of a Ferrari needs to prove how wonderful his car is by driving through the town, I'll never know.
Title: Re: Exhaust Rapping
Post by: BigJim on 21.09. 2020 20:40
Just seen on Google maps a for sale sign going up in Musky's neighbour's garden! The one start up was enough to get them looking for somewhere more isolated (joke)!
That bike is the DB's Musky, you can start it in my drive if you ever visit this Isle.
Yep GB, the police have disappeared. Am happy with my refitted baffle tho has reduced the goldie bark to a gold flash growl.
 *shh* *wink2* *dribble* *beer*
Title: Re: Exhaust Rapping
Post by: Rocket Racer on 21.09. 2020 22:11
G'day Fellas.
Well put your ear plugs in or turn off your hearing aids. Yasser asked for it  *ex*
My first ever attempt at a video and my first post on YouTube. Only taken me all bl@@dy afternoon.
https://www.youtube.com/watch?v=ckJ5PU8CQGg
Cheers

made the hairs on the back of my neck stand on end. music to my ears. Need to pull finger and build my track bike! Do like the swan necks and the high pipes. not forgetting the twin port head *wink2*.
Title: Re: Exhaust Rapping
Post by: Jules on 22.09. 2020 12:53
Good looking (the bike not you Musky ha ha), and the sound is very amenable actually, I thought the starting was very good too for the level of tune Musky, well worth the effort of showing, thanks
Title: Re: Exhaust Rapping
Post by: metalflake11 on 22.09. 2020 14:37
I've had a go on Youtube now as well!  *smile*

Straight through pipes....... I did this video 6/7 years ago, to show somebody how the Sparkbright digital voltmeter works, and the charging light behind the carb. People often comment how quiet it is for straight through pipes, but around 70/80mph it sounds 'slightly' different.

 It has 24 (yes four) teeth on the engine, and 21 on the gearbox so it lopes along on the motorway where a lot of my mileage is covered.

https://www.youtube.com/watch?v=i0F54EIHtqo&t=55s
Title: Re: Exhaust Rapping
Post by: Black Sheep on 22.09. 2020 15:28
The exhaust note depends on resonance so is affected by the length of the pipe and rpm and of course the silencer/megaphone/trunpet if any fitted. As we all know valve overlap and pressure pulses in the exhaust result in increased cylinder filling at a specific rpm with the effect reducing and eventually reversed away from that rpm. You have a similar effect on the inlet side of course. Anyway, there is a sweet rpm for any engine which will sound good (depends on your definition of good) and there is another where it sounds pretty rough. An example is the Manx Norton which comes on cam rather sharply at 5,200 rpm and at 3,500 rpm is pretty gutless and sounds dreadful. 
Title: Re: Exhaust Rapping
Post by: Yasser on 22.09. 2020 18:02
I haven't  seen any engine doing so much rap than the orinaly posted BSA in Cuba. I am convinced there is a trick behind it that the owner knows very well and worked on it to make it easier.
Title: Re: Exhaust Rapping
Post by: muskrat on 22.09. 2020 20:49
G'day MF11. Sounds very nice. Now I need to see a vid out in the light of day.
 
G'day BS. Your right of course, my pipes were tuned to the A7SS for 6500rpm. The 357 cam comes in at about 4500. I only took her up to 4000 in the video, we know what happened last time I revved her up to 7000 in neutral  *pull hair out* *bash* *work*. For those that missed it https://www.a7a10.net/forum/index.php?topic=10630.msg79189#msg79189
 
G'day Yasser, yes the one in your video sounds a lot crisper. Open mega's help but it'd probably suffer megaphoneitis till it got on the cam

Ha, just noticed I was wearing the forum Tee shirt and the print on the wall. Now I'm in trouble for wearing a good shirt in the shed.
Cheers
Title: Re: Exhaust Rapping
Post by: Yasser on 30.10. 2020 18:01
Check out this video and you will understand better

https://youtu.be/9NhtF7A1LZY

Title: Re: Exhaust Rapping
Post by: Jules on 31.10. 2020 09:32
interesting video Yasser, thanks - spoilt by the rapping exhaust though LOL, sorry  *shh*
Title: Re: Exhaust Rapping
Post by: olev on 01.11. 2020 03:32
Gday Yasser,
What sort of bike is that in your latest video?
It can't be a BSA - its not shaking enough.
and you can actually see things in the rear view mirror.
cheers
Title: Re: Exhaust Rapping
Post by: Yasser on 01.11. 2020 13:56
The camera is over a Norton Dominator 99 but the rapper is a BSA Golden Flash with a 357 cam