Guys, got an 08 Street Glide, and I installed Bassani slip on megaphone mufflers. No download flash, no high flow intake or filter, no tuner. What is the popping exactly ? Someone told me it's caused from a lean condition. Can someone please explain this to me ? Sorry, if it's a stupid question. Thanks, in advance...

 

Popping occurs when the fuel- air ratio is perfect light up all at once instead of burning at a more controlled state. In some situations, like decel this perfect fuel charge will collect in the pipe and get lit on the next exhaust strokes flame front. This in itself doesn't mean your engine is running lean, but the exhaust change you made may have altered the speed and distance of this charge making it more likely to light up and pop. By making it richer, it is no longer in a perfect state to explode in the pipe and exits. Going leaner on the mixture is not really an option for the engine, but that would also screw the ability of the fuel to explode. That's more or less how it works. Like most of us with aftermarket exhausts, it's a good tune, or different baffles and back pressure to stop this annouyance. Ron

 

During my own search for info on this subject I found this article helpful. Probably the first thing you should check for is exhaust leaks. Sometimes the problem can be cured by simply tightening a clamp.


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. 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.

 

Here is a simple answer that doesn't require a engineering degree to understand:

The factory set up the fuel injection to keep the EPA folks happy. If you are under throttle and suddenly let off the throttle, the computer automatically takes the bike to maximum lean, so as to try to keep excess fuel from being burnt.

This can be tuned out of it. I tuned it out of mine. It's running 13.7 Air to fuel ratio, which is optimum....not rich at all.

"popping means it's lean"~~~~~"black smoke means it's rich"

~Joe

 

And if you want the even simpler answer:
It's extra gas in your exhaust which explodes because of the hot exhaust pipe.

 

traveler - i have XIED;s and do have the black smoke on start up till bike warm. is this bad ? has the stage 1 HD download with SERT. have some popping if i rev over 5k rpm and then backoff the throttle. seeing the black smoke -- being to rich then ?

 

The "easy" answer is that your bagger needs to be tuned on a DYNA with the SEART (Screamin' Eagle Race Tuner), or a Power Commander. If you bike is pushing black smoke when it's cold, it because the computer is adding fuel as a "choke" until she is warm. The degree to which it is putting out black smoke is a concern. As far as the popping, I'm telling you for my own personal experience, that is an indicator of a lean condition. Honestly, it sounds as though your mufflers and intake were added without a tune. You spent a ton of cash for a new bagger.....do it right, and get a SERT or PC with DYNO tune.

P.S. I don't know what and XIED is. I know what an IED is.....we lost a guy to an IED in Iraq in 2004.....

~Joe

 

XIED= Extreme Inline Enrichener Device .. Simply Put Jumper Wires from the 02 Sensors to the ECU by means a of Resistor to Vary Voltage to Richen the A/F from 14.7 to 13.8 works well at 2,000 RPM and Above ... Well still Pop on Decel and Idle hot in heavy traffic. Already ordered a Power Commander to Tune it Properly..

 

ok, thanks.

I still recommend a REAL tune on a DYNO with SERT or PC III.

~Joe

 

I was digging around on another site and saw this just some food for thought.

Why does adding fuel in over-run change the backfiring?

The answer to this one is not what everyone has been led to believe. Hang with me on this one.

It takes three things to get backfiring in the exhaust. Heat and quite a bit of it, unburned fuel and air containing 02. Leave out any one of these things and the backfiring will not happen.

So how do each of these happen at the same time. The first one to address is unburned fuel in the exhaust. There is a couple of ways that this can happen. First is that for some reason, the the spark failed to light the compressed fuel and air in the combustion chamber. This can be either the spark plug failed to spark, the mixture was too lean to light or the mixture was too rich to light. All of these combinations will result in 02 and raw fuel ending up in the exhaust just waiting for an excuse to blow. The easiest way to get a source of heat is the next time the spark does manage to get the mixture to fire and when the exhaust valve does open a small bit of this following flame fights the mixture left over from the last miss hit and BANG you get a backfire out the exhaust. this is kinda rare but can happen.

The more likely thing is that the mixture was too rich and when the spark happened the fire ran out of fuel before it ran out of fuel and the left over fuel ended up in the exhaust just needing heat and a little o2 from somewhere. The place that is most common to find a little frest air is from the exhaust mannifold gasket that is leaking or from the joint between the head pipe and the muffler. At this point there is plenty heat floating around for the mixture to relight and BANG, you get a backfire.

The last possibility that I had not considdered was to fix this entire issue by flooding the motor in over-run with way too much fuel and and killing the heat in the exhaust and forcing the temps low enough to kill the possibility of a backfire. It turns out that there is apparently a 1ms minimum Pulse Width in the a Sporty code and in some situations this is still too much fuel to get all the way down to 14.7.

Remember that if the motor is at 14.7 or leaner in over-run there is just no fuel left in the exhaust and there is now way a backfire can happen. The problem is with the 1ms min PW you may never get down to 14.7

The way some of the Harley codes get around this is to kill fuel entirely in overrun. The problem with this solution is you can often feel the injectors suddenly turn back on at some point right before idle takes over or the throttle rolls back on. All fun and games of EFI tuning.

A big thanks to Steve at www.nightrider.com for pulling all this together. The same guy that does the XIEDs.