Suzuki GSXR Forum banner
1 - 20 of 31 Posts

·
Registered
Joined
·
163 Posts
Discussion Starter · #1 ·
kind of a quick question...\

i got the bike w/ this exhaust already on it, by looking at the picture... is it just a slip on or is that box underneath aftermarket too? I only ask because when i slow down it pops. i've heard it's something along the lines of it pushing out more air than the bike is taking in? or, the other way around? i'm not sure, I hope that makes sense.

I take it in for the 600 miles checkup this weekend and i'm going to have them address that issue. I'm just kinda curious if anyone else might know whats up to curb my curosity.

thanks
 

·
Registered
Joined
·
380 Posts
It's running Rich, the popping is unburnt gas. Also that is part of the after market exhaust, It's the Catalytic converter.
 

·
Registered
Joined
·
1,083 Posts
The bike is most likely running LEAN. Do a search on disconnecting the PAIR valve. 99.9% of the time, if you disconnect the pair at the airbox and plug the hose and the open tube in the airbox...Popping on decel will stop. The can below is an aftermarket expansion chamber that comes with the exhaust. That is not the stock Catalytic converter.
 

·
Premium Member
Joined
·
9,268 Posts
I have to go with Loki on this one, at least about being too rich anyway. Excessively lean conditions can cause rough running, but not popping. Disabling the PAIR valve has the most effect on a rich running engine, and little to no effect on a lean running one.
 

·
Registered
Joined
·
4,175 Posts
+1 on unburnt air/fuel in teh exhaust system.


4-stroke motors dont use expansion chambers in exhaust systems. expansion chambers are designed to create vacum in the cylinder using sound waves created by the combustion process in 2-stroke motors that have no valves to increase horsepower output.


its a catalytic converter and baffle combination.
 

·
Registered
Joined
·
1,083 Posts
I have to go with Loki on this one, at least about being too rich anyway. Excessively lean conditions can cause rough running, but not popping. Disabling the PAIR valve has the most effect on a rich running engine, and little to no effect on a lean running one.

You are of course entitled to your opinion but a lean condition will cause the bike to run better to a point (until you burn a hole in something). A lean condition is a relative term. You will always have unburnt fuel in your exhaust because of the following. Engines are tuned to run richer than the Stoiciometric ratio of A/F so they don't run too hot. The Stoiciometric mixture is the "Perfect mixture" where all fuel and air is used in the process. You would make the most power but in this instance the heat produced would damage the engine. To say an engine is running lean is to say that you are running on the "Lean" side of the desired mixture. If you get to the Stoiciometric ratio or above, you are burning something.

When you are running on the lean side of the desired mixture, the exhaust gas is hotter than if you were at or below the desired mixture. In fact it is hot enough to cause re-ignition of unburned gas and combustion products. When you roll off the throttle, the throttle bodies drastically reduce the amount of air flowing into the engine (Basic carb/FI theory), The combustion process in the cylinders drops drastically. This leaves a bunch of fuel/combustion products in the cylinder. When the exhaust stroke occurs, these products are expelled into the exhaust headers. If the exhaust header is hot enough to ignite these products due to running the bike at a leaner than desired condition, and there is air present to support combustion (PAIR valve provides the air), ignition will occur in the exhaust header. When you disable the PAIR system, you remove the air source and therefore ignition in the exhaust cannot occur.

Usually a rich condition causes a backfire (Airbox ignition) or poor running. A lean condition causes Afterfire (Exhaust ignition) and more power but higher engine temperatures.

Basically in the old days, this is one of the ways you adjusted jets on a carburetor if you didn't have an A/F meter.

Here are some links to the issue Not all about bikes but still applicable.
http://faq.f650.com/FAQs/BackfiringFAQ.htm
http://en.allexperts.com/q/Motorcycle-Repair-837/Deceleration-exhaust-popping.htm
http://www.classicmotorcycles.biz/mechanics/exhaust/thread108.html


I can give you about 10 more that all say the same thing and actually a Carburetor tech manual that I will have to scan to show you but Backfiring on Decel is caused by a lean condition.
 

·
Registered
Joined
·
1,083 Posts
+1 on unburnt air/fuel in teh exhaust system.

its a catalytic converter and baffle combination.
I used the wrong terminology, not an expansion chamber but there is no catalyst in the chamber. It is just an extension of the muffler called a sub muffler.
 

·
Premium Member
Joined
·
9,268 Posts
When I use the term "lean", I mean leaner than the stoichometrically correct mixture. Remember that the A/F map isn't constant over the entire power band. You are correct in that these engines have to run rich at high power and throttle settings, but they can run perfectly well at the stoichometrically correct A/F ratio or leaner at cruise power settings.

Most newer car engines are actually run lean of the stoichiometrically correct mixture all the way through their power band. They are able to do this through 02 sensor feedback loops (there is an excess of air in this condition), low compression ratios, relatively low power outputs, and knock sensors to retard timing. Note that some new bike engines also use 02 feedback loops to run in a lean condition, although a high performance bike engine will still run rich at high power or throttle.

As a side note, aircraft engines have many of the same problems that high performance bike engines have with respect to detonation, and high cylinder head and valve temperatures. At high power settings, they can either be run very rich, or lean. Running them rich causes fuel to cool the cylinders and valves and control detonation, and running lean causes excess air to do the same thing. This is actually the preferable way to operate these engines, as they last longer, have less fouling and carbon buildup, and are more efficient. Of course, they run at the same speed for hours on end so it's possible to practically control the mixture to keep the engine in a safe operating regime.

There are basically two ways you can regulate mixture control for engines that run lean. One is using oxygen sensors, like most modern cars, and the other is by exhaust gas temperature, which is used in piston aircraft. If you were to measure the temperature of the exhaust, you would find that as you lean the mixture from a rich condition, the temperature of the exhaust increases. It peaks out at some point near the stoichiometrically correct mixture, and starts to decrease as you further lean. Roughly 50 degrees rich of the peak EGT is the "best power" mixture for most engines, and the highest valve and cylinder head temperatures occur at about 25 degrees rich of the peak EGT. So actually, some of the most destructive conditions for an engine are still on the rich side. Typically, once you're past 50 degrees lean of peak EGT, you're out of the region where detonation and valve burning is an issue.
 

·
Registered
Joined
·
1,083 Posts
When I use the term "lean", I mean leaner than the stoichometrically correct mixture. Remember that the A/F map isn't constant over the entire power band. You are correct in that these engines have to run rich at high power and throttle settings, but they can run perfectly well at the stoichometrically correct A/F ratio or leaner at cruise power settings.

.
Can't speak for newer cars and definitely not for airplanes and I agree that the Stoiciometric ratio would not cause damage under light loads, but I don't believe that a bike ever runs at the Stoiciometric mixture. I could be wrong but you will have to show me a graph. I used to have a curve of dyno tune I had done on a fuel injected bike, at the bottom was an A/F ratio but I can't find the sheet.
 

·
Premium Member
Joined
·
9,268 Posts
Can't speak for newer cars and definitely not for airplanes and I agree that the Stoiciometric ratio would not cause damage under light loads, but I don't believe that a bike ever runs at the Stoiciometric mixture. I could be wrong but you will have to show me a graph. I used to have a curve of dyno tune I had done on a fuel injected bike, at the bottom was an A/F ratio but I can't find the sheet.
I agree with you on that.
 

·
Registered
Joined
·
38 Posts
how about a power commender. see your bike is set up for the stock exhaust. so when you switch you need to run some new maps. if not it will run like you still had the old exhaust.
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #13 ·
how about a power commender. see your bike is set up for the stock exhaust. so when you switch you need to run some new maps. if not it will run like you still had the old exhaust.
That's what i'm thinking, but the retarded sales guy said it wasn't going to be an issue. Can it be re-maped without the PC? If not, i guess i'll be getting one sooner than I thought.
 

·
Registered
Joined
·
1,083 Posts
All of my bikes popped on decel with a new exhaust even after a power commander. Until I disconnected the PAIR.
 

·
Registered
Joined
·
178 Posts
listen to Formula 1 cars on decel .... that snap crackle and pop is ALL about lean.
You get away with it because there is no load. They do it for fuel economy mostly .... and so they aren't loaded up when they get back on the throttle.
 

·
Registered
Joined
·
155 Posts
Dude, you are running to lean, to make sure pull the plugs and if they are chaulky white it's an indication that the bike is running to lean. These bikes are set lean from the factory and putting on an after-market exhaust makes them leaner. Do PCIII and get it mapped on a dyno machine, they will hit the exhaust curves perfectly.......Peace out.........:cool:
 

·
Registered
Joined
·
1,353 Posts
Just because it is popping doesn't neccesarily mean it is running rich or lean. The popping is indeed caused by the PAIR system. The PAIR is an emissions system designed to inject air into the exhaust track to burn unburned fuel so your NOX levels are within guidlines. Extra fuel is injected into the exhaust system when you decelerate for two reasons. 1. The engine is slowing down and your electronics cannot react quick enough to maintain the right amount of fuel for the RPM and 2. Running too little fuel while the motor is slowing down can cause detonation and ultimantly burned parts. As I said, the extra fuel that is not needed is passed through the cylinder, into the exhaust track. Since it is superheated, injecting air causes it to "explode" thus creating the popping. Remove the PAIR system and it should go away.

With that said, I believe that anytime you change the exhaust or intake system, you should remap with a PCIII or similiar.
 

·
Registered
Joined
·
396 Posts
So...the ultimate question is if the poping actually harms the bike?
 

·
Registered
Joined
·
572 Posts
also if it is running lean is it going to be running slighty hotter than under the right a/f ratio??
 
1 - 20 of 31 Posts
Top