sxv backfiring on decel - is the following a possible solution?

[unowned]

i'm just wondering, if the exhaust flow restrictors are still intact on a supposedly derestricted bike, can this cause backfiring on decel?



In the meantime ill have a look at my exhaust... where exactly are these things located?



i took it to the dealership for service...it was running fine before - no popping or backfiring...the dealer did an oil change, said they removed some broken metal bits inside the exhaust and updated the ecu map....i got it back and its backfiring like crazy...

[SXVINWA]

It would be a total guess with the info provided. It might be nothing more than a Idle CO adjustment or it could be TPS values. Some maps run lean while others run rich without correction. Knowing what map was in prior and what is loaded now would help. Poor idle and stalling at idle would tend to support a bat TPS setting. I would think loading a derestricted map into a bike that still had restrictor cones would run way rich and be easy to spot, but it doesn't hurt to pull the subframe off and check. It would be far worse to load a restricted map into a derestricted bike, I believe. Another possible cause could be gaskets. If they found bits of metal in the exhaust; where did they find them? Did they pull the exhaust off the cyls?

We could come up with all kinds of reasons for decel popping, but the bottom line is you need to be confident that the ECU has been set up correctly first. Others may have a better idea.

JMHO

[Dark]

Mine pops like crazy on decel with the silmoto map and silmoto enduro exhaust. No complaints here.

[unowned]

Mine pops like crazy on decel with the silmoto map and silmoto enduro exhaust. No complaints here.

whether its running lean or there is a exhaust leak causing it - it may not be detrimental but backfiring certainly can't be good for a bike

It would be a total guess with the info provided. It might be nothing more than a Idle CO adjustment or it could be TPS values. Some maps run lean while others run rich without correction. Knowing what map was in prior and what is loaded now would help. Poor idle and stalling at idle would tend to support a bat TPS setting. I would think loading a derestricted map into a bike that still had restrictor cones would run way rich and be easy to spot, but it doesn't hurt to pull the subframe off and check. It would be far worse to load a restricted map into a derestricted bike, I believe. Another possible cause could be gaskets. If they found bits of metal in the exhaust; where did they find them? Did they pull the exhaust off the cyls?

We could come up with all kinds of reasons for decel popping, but the bottom line is you need to be confident that the ECU has been set up correctly first. Others may have a better idea.

JMHO

Thanks, i'm somewhat confident that the tps and mapping were set up properly..it idles fine, accelerates fine - slightly jerky at lower gears and rpms

I'll take a look at the plugs for lean/rich conditions




This is what i need to take out and look at the inside of yes?

[SXVINWA]

Right hand side of your pic, where the pipe enters the muffler body. One was installed in each pipe. When I checked to ensure mine were removed I just pulled the whole subframe assembly as one piece, leaving the head pipes installed.

I think you are going to find them removed. Description of how it's running sounds too good for them to be in there. I'd be leaning towards a gasket issue first, if you are confident about the ECU settings.

[Tyke]

I would say its almost certainly an air leak in the exhaust system somewhere.

All pipes wear at the joints, particularly the after market versions.

Two main places to check would be the headers to the cylinder and the joint to the muffler

I have silmoto pipe and map and its quiet when first fit but after a few rides it starts to pop, then its time to remove and re seal the joints.

[Markee]

I would say its almost certainly an air leak in the exhaust system somewhere.

All pipes wear at the joints, particularly the after market versions.

Two main places to check would be the headers to the cylinder and the joint to the muffler

I have silmoto pipe and map and its quiet when first fit but after a few rides it starts to pop, then its time to remove and re seal the joints.

What do you use to seal the joins?

[swerver]

I stole this from revcounter:

Re: popping on the overrun

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.

[unowned]

weird, i found a piece of shrapnel stuck inside my silencer unit (that fat exhaust muffler body thing)...havent gotten around to the header pipes yet...i think i will replace the exhaust gaskets at this point as well...

anyone have recomemndations for exhaust gaskets?? OEM or otherwise?

[rocketnz]

OEM, and double them up i have read here.

[unowned]

Thanks for the feedback folks...

i understand some backfiring is normal...but the amt im getting is quite abundant and sometimes the backfiring is so powerful that it makes my bike shake - im almost sure this is uncharacteristic behaviour of this bike

im having a tough time prying off the muffler body/silencer/big unit from the header pipes...i've unscrewed all the fastenings as far as i can tell, is there some sort of adhesive between the pipes or do i just need more elbow grease?

Also, the rock in the muffler body is jammed/wedged in the inlet pretty tightly, i spent an hr trying to pry it out, but there's not quite enough clearance for me to get anything like pliers or clamps to grab the rock...the rock itself is blocking the inlet pretty good so maybe its a source of the backfiring?

here's a pic

https://lh6.googleusercontent.com/-L...5B1%25255D.JPG

[SXVINWA]

Interesting pic. I can't figure out how anybody could get that in there without noticing at assembly.

Mine had no sealant between the headpipes and the body; just the springs.

[wilmar13]

I am pretty tired, but... WTF is that; a rock???

[unowned]

yup...its a big one...

good/bad idea to try to drill the rock? There's not enough clearance for me to get anything through to pry it out

[wilmar13]

yup...its a big one...

good/bad idea to try to drill the rock? There's not enough clearance for me to get anything through to pry it out

I would not feel good about removing it without understanding how it got there... Are you positive it is actually a rock or is it a section of baffling or packing made of ceramics?

There is no way in hell a rock can get in there short of deliberate sabotage, or is that what probably happened? Do you have a 6 year old that likes to find interesting places to hide rocks perhaps?