Exhaust popping


Just a general wondering: the stock exhaust on my SV650 doesn’t pop or bang when I let off the throttle. Why’s that? I’d quite like it to!

What do aftermarket cans do to the gas/fuel/fairy dust to make it do that?

Thanks! :slight_smile:

I’ve just had a 3-into-1 system put onto my triumph street triple and I notice that when I decelerate at about 4k rpms, I get a pop pop thats quite loud… it does sound great, but I was just wondering whether it should do it or whether it means its not been remapped correctly?

i get it all the time on the SV1000 and have found a way to make it do it on command. When you’re shifting down into first keep holding the clutch in for a couple seconds longer than you would normally after shifting and then let it out. Just don’t do it when it’s nasty outside as it gets slippery.

just burning unused fuel not going to harm the bike but it could be mapped to stop it if you don’t like it

If you have a CAT on your bike, I believe you wont get a popping noise…
As previously stated its the unspent fuel. :smiley:

The 3 in 1 has the CAT removed and you should have had it remapped for sure! There is Triple map for your zorst, lets see your pics? Was it easy to change over?

I’ll give that a whirl - thanks, Viggen! :slight_smile:

Time for a new zorst after tax-payment time, methinks. CAT-free. :smiley:

I read about this recently on another forum…copied and pasted below:


*it’s caused by a lean pilot circuit (or an air leak if it’s a fault)
read this…

Burn Baby Burn

The last thing I want to address today is the subject of deceleration backfire, or “popping”. This topic generates a lot of concern from inexperienced riders, or even from experienced guys who just hate the noise, so lets take a look at what causes it. But first things first, lets define the issue:

Deceleration Backfire is caused by fuel burning in the exhaust manifold or header.

No ifs ands or buts, that’s what causes it. But the bigger question is how does gas get there in the first place, and that’s a bit more complicated. Generally, there are a variety of ways it gets there, and a variety of things that can make the backfiring worse. But there’s a kicker, and something you should understand before we go any farther:

A motor in perfect tune will exhibit deceleration backfiring.

Therefore, just because your motor is banging it up, doesn’t mean there’s anything wrong. And consequently:

Getting rid of the noise means de-tuning your motor.

Yup. If you’ve jut got to eliminate that popping, you’ll have to accept the fact that your motor is going to be forced to run rich to do it, and that isn’t necessarily a good thing. So lets talk about what causes the problem.

Ok, so you’re riding along at some given rpm, and suddenly you decide to decelerate, and you reduce the amount of throttle. This causes an “overrun” – that is, the motors rpm is turning faster than the fuel provided can support, so the motor begins to spool down. This causes a couple of things to happen.

First, when you close the throttle, you are also closing the throttle plates. This reduces the air and fuel flowing into the motor, and increases the vacuum (lowers the pressure). This results in less air and fuel in the cylinder during the power stroke, which in turn results in a lower pressure in the combustion chamber. Remember I said earlier, that the A/F mix burns faster in proportion to the pressure applied? Well, when we reduce pressure this way, the mix burns slower. This results in two things happening.

  1. The lower burning fuel generates less heat, and the cooling effect of the non-burning fuel tends to “quench” the flame front, or slow it down even further. Because the mix is burning much slower, the exhaust valve can open before all the fuel is consumed, and the unburnt fuel is ejected into the exhaust.
  2. The engine designers, in order to promote smoother idling and better combustion, retard the spark when the throttle is shut, and this results in the mix being lit later.

So, now we end up with unburnt fuel in the exhaust, and burning fuel being ejected into the exhaust, and bang! Backfire. In addition, Honda has added a device called a “programmed air injection valve” (Pair Valve) that actually injects some fresh air into the exhaust to help this process along – since fully burning the fuel results in cleaner exhaust. So the backfiring is not only a normal part of the engines operation, it’s also intentionally amplified by Honda! Of course, normally, that massive bazooka pipe Honda hangs on your bike hides most of the noise, but it’s there, even when you can’t hear it.

So the bottom line, is: That backfiring is perfectly normal and expected. If you’ve just got get rid of it, that’s up to you. You’re entitled to set your motor up the way you want, and your goals are your goals. But don’t refer to it as “fixing” the popping. Rather, the correct way to think of it is “de-tuning a bit to get rid of the popping”.

There are a few ways you can do this.

First, use the stock pipe. It will hide the sound, by absorbing it into mass, and masking it with the larger baffle space. Second, you can add more fuel during deceleration. This has the effect of raising the chamber pressure slightly, which burns a little more before the exhaust valve opens. Lastly, you can remove the Pair valve, which reduces the amount of available oxygen in the pipe to burn the unburnt fuel.*

so by making the bike run leaner the bike will pop more? seems funny i would have thought making it run rich would do that?

My er6 with a cat pops.

When I’ve setup carb cars properly they always pop’ed heavily on overrun, and we’re not talking performance engines.

That’s interesting - cheers, fella!

I assume that’s why my engine note gets really bassy when I close the throttle. It’s the backfires being muffled by the huge stock pipe…

Sounds good in tunnels, that does. :smiley:

Unless I’m completely wrong and it doesn’t happen at all on fuel-injected bikes like mine?

it does happen but the stock pipe does a lot to block it out from being heard. new end can and you’ll hear it straight away. ratty swears by the blue flame .

Ratty gave me a blast of the Blue Flame at BM - it sounded amazing. They’re quite pricey though, aren’t they?

What are Carbon Can Company ones like?

Would I need to go to a specialist place to get the fuelling sorted out after it’s fitted or would it be OK straight out of the box?

So many questions!

if it’s just the end can you’ll be fine as the sv runs a bit rich anyway. i’ve got devil racers on my sv and had it on the dyno it ran rich low and high in the rev range but pretty spot on in the mid range where you want it most. i’ve not had any electric poking around on mine and it’s all good.

sod the blue flame

this is what you want if you want that sound at the best the SV can give


Alternatively get a single :wink:

My CB500 didn’t seem to pop at all till I fitted an after market exhaust with a removable baffle. Now it does it all the time and even spits flames if you rev it at the redline.

The noise is really fun. It can affect your riding style for the first few weeks though as you try to make it pop as much as possible till the novelty wears off.

what do you mean novelty??? i can’t get enough of it:w00t: just like when my saab use to spin the front wheel when shifting up at 100mph.

The VMax pops more on the overrun when it’s cold than when it’s warmed up a bit, does make a nice noise though, quite teh sexeh :smiley:

I saw a bloke at box hill once ,used to ride up past the crowd pull out an imaginary gun flick the ignition switch on and off and point the imaginary gun at the crowd and it made an enormous BANG! was funny seeing people duck down while he pointed his fingers at them :smiley:

Ok so what is the actual procedure for doing the igntion switch thing? Is it?

  1. Roll along in 2nd

  2. Pull the clutch and hit the kill switch

  3. Keep the clutch pulled and flick the switch back to on.

  4. Dump the clutch and bump start it.

Or do you have to let the clutch out slowly? Or have I missed a step?