A question of cans?

[Toph]

Thanks everyone for your valued advice..and thanks for the offer of fitting Si, nice one mate!!

[Nooj]

Wot Simon says, they run a little rich as standard, so a new can will improve the running a bit. Why not do the whole job and fit a K&N filter as well? It'll make it run even smoother.

[Harry87]

Loud cans are for attention whores ;D ;D

Though I have looked at a few for my er6, especially after the stock downpipe cracked at a weld.

Another advantage is often the reduction in weight. My stock exhaust weighs a ton, and when I took it to a motorcycle shop, they actually said, sorry we don't do car exhausts.. :

Aftermarket, slip ons, race cans, or whatever, cost quite a bit too, from what I've seen. The custom choice is always going to be expensive though; look at Pizza Hut for example.

[Mark_Able]

Toph, I had exactly the same model 'Cat as you, and it did need rejetting with an ART can. I wouldn't buy an ART can again, or any other cheap can in fact. If I'd bought a decent race can, it may have been a different story. The ART can put a big flat spot right in the middle of the rev range, just where it needs to be when going for an overtake. So if you didn't have the right gear, it could be a bit scary. I'd go for a proper race can with a road legal baffle (still sounds fruity), so as there's less chance of upsetting the fuelling.

[Scotty]

A mate of mine has a Cat with an end can (possibly a Micron) on it, maybe a filter too, but his has been properly set up with a Dynojet kit on a dyno and for a carburetted 600 it sounds and goes a treat. It's certainly way sharper than any old 600 with a can just slung on it. Popping and banging on the over-run isn't big or clever, it means that your bike is running like **** and needs setting up properly. :P

[Mitch9128]

Crap

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.

[Jon_W]

Usually all that popping and banging means is that air is getting into the exhaust. Seal the can properly and it'll stop. Had this on the Sv years back.

Other than that it is a sign of poor timing, or bad mixture, but this is less likely.

[Kevinb]

What do you perceive as being wrong with 'a bit quiet' ..?

I've got Akro's on the MT (baffles out) and non standard on the Bonnie. Standard Bonnie pipes just sound so wrong (like a sewing machine)

They both burble at 30mph so not to annoy people in towns & villages but just sound great on the open road.

[Scotty]

Very impressive Mitch, was that all your own work or painstakingly copied & pasted from somewhere else?
I refute "your" argument; my trackbike runs a 0.3mm thinner than stock head gasket, full Arrow race system and a Power Commander so it's not de-tuned by any stretch of the imagination. Additionally it doesn't pop and bang on the over-run because it's been set up properly.
Maybe we'll have to agree to differ, but I've heard more than enough rough-running bikes with end cans on them over the years, nothing like as pleasant as the sound of one that's been done properly...

[Mitch9128]

Are you saying that a slip on causes rough running? Hardly likely is it? More like the bike was fettled by a numpty. A slip on merely let's you hear the noise silenced by emmissions laws and oem cans.

I guess it's a safe bet your track bike has had the secondary air system removed?