Exhaust Popping during slow down.

[aaron210]

I have a 2005 Kat 600. Recently I have Ground out the welds in my exhaust, installed a two brothers M2 slip on, and a Ivans Jet kit at 4 turns out on the A/F Screw like it says, with a STOCK air cleaner. I put everything back together and Synced the Carbs and it runs Great but when I am running and slow down at a stop sign or light I have some light popping comming from the exhaust and I wondered what I can do to get rid of that. Do you think the A/F Screw is a little too far out? Should it be at 3 1/2 or 3 3/4?

[Tmod]

I have a 2005 Kat 600. Recently I have Ground out the welds in my exhaust, installed a two brothers M2 slip on, and a Ivans Jet kit at 4 turns out on the A/F Screw like it says, with a STOCK air cleaner. I put everything back together and Synced the Carbs and it runs Great but when I am running and slow down at a stop sign or light I have some light popping comming from the exhaust and I wondered what I can do to get rid of that. Do you think the A/F Screw is a little too far out? Should it be at 3 1/2 or 3 3/4?

Might want to check for leaks in your exhaust.

Tmod

[steves]

Popping under no load, or popping on decel?

[aaron210]

under load decel braking still in gear. I was thinking I was too rich on the A/F screw and it is making it pop.

[steves]

I found this on the interweb for what it's worth

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.
http://www.vtxoa.com/forums/viewtopic.php?t=28918

[aaron210]

So you are telling me everyone on here with after market exhaust and a jet kit is going to have the after pop in their exhaust?

[Tokalosh]

I cant vouch for everyone, but I've had my Kat dynoed twice fitted with 2 different jet kits and a slip on. I still get poping on deceleration. Something I've gotten a custom to after all these years.


Tok

[dewke]

I'm glad to read that because i put my slip on last fall and immediately noticed the deceleration backfire. I just figured it was normal because the bike had just been checked out, and as it turns out it is.

[tnez21]

I have a 2005 Kat 600. Recently I have Ground out the welds in my exhaust, installed a two brothers M2 slip on, and a Ivans Jet kit at 4 turns out on the A/F Screw like it says, with a STOCK air cleaner. I put everything back together and Synced the Carbs and it runs Great but when I am running and slow down at a stop sign or light I have some light popping comming from the exhaust and I wondered what I can do to get rid of that. Do you think the A/F Screw is a little too far out? Should it be at 3 1/2 or 3 3/4?

You might still be popping because i dont think Ivan's kits are designed to be used with ground out headers, just a slip-on and an advancer. You might need a Factory Pro kit that allows more jetting options.

[arsenic]

no, you're all wrong popping on decel is caused to running lean, adjust the a/f screws out more to run richer.

There are a few ways you can do this.
Second, you can add more fuel during deceleration.

[aaron210]

isn't 4 turns out for Ivan's already pretty rich? You think I should go richer than that?

[arsenic]

it's obviously not rich enough, if you're popping on decel, but yeah it's generally really rich. my personal opinion, is get a dyno run with an EGA

[MiDnIgHtKat]

Had the same problem it was nothing more then a leak

[scottynoface]

My bike is completely stock and pops a bit on hard decel, I'm used to it

[scaryfast777]

Normal