Brissy Riders Club

Subject: Re: Exhaust popping? Sun May 18, 2008 7:31 pm

My bike does it too. If i burt out in 2-3 and let the throttle goes it pops and farts like an old granny on Metamusil....
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Subject: Re: Exhaust popping? Sun May 18, 2008 9:58 pm

Guest

not really, even mine still does it.... but i have a 1000 so you gotta catch me to tell me how bad it sounds.

Subject: Re: Exhaust popping? Sun May 18, 2008 11:48 pm

lol....you're a 1,000, we're 600. Why don't you and Mark on Bumble Bee go head to head and see how the 1k's fair?
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Zorgoth, the god of Zatheism

Subject: Re: Exhaust popping? Mon May 19, 2008 1:13 am

P Plater Joined : 17 Apr 2008 Posts : 90 Location : Aus

Many of the most perfectly and 100% properly tuned bikes have backfiring/popping under deceleration, thanks to aftermarket mods combined with the stock PAIR Valve that many bikes have. aka "Pulsed Air Injection".

With some bikes, like the GEN2 Hayabusa, it is simply a matter of inserting a marble into the PAIR intake port. On other bikes like the GEN1 Hayabusa, you must remove an entire assembly.

Often backfiring is a normal and natural thing under deceleration. Perhaps disabling the PAIR valve is even bad for the environment... But I guess the motivation to not have backfiring is to draw less attention from the police and dickheads who will inevitably say "omg wtf is wrong with your bike man!!!!!!".

My favourite explanation of the PAIR Valve:

"The Pair Valve is a pollution control "Pulsed Air Injection" device, designed to "wash out" the purposely rich exhaust of the new metric bikes in order to pass EPA restrictions for import in the United States and other countries with similar restrictions. Many foreign designated models do not even come with a pair valve, although all other aspects of the bike's engine are the same. (The triangular (or oval) box is a tool box on most foreign models)

The sole purpose for the Pair Valve is to passively "Inject" fresh air into the exhaust system at the exhaust port, to cause ignition of unburned fuel vapor *before* it leaves the exhaust pipes, or to thin out the mixture with enough air to fool the sniffer machines. Unburned fuel vapors enter the exhaust system whenever you back off the throttle, or gear down. When you close the throttle, as in gearing down or slowing down, the drop in vacuum at the intake port allows the Pair Valve to relax and open and allow air from the air filter box to be "siphoned" into the exhaust port by the negative pressure at the exhaust ports. (there are reed valves in the pair valve to prevent backflow from the exhaust to enter the pair valve and airbox during roll-on and subsequent positive exhaust port pressure)."

Many people who have replaced their exhaust system with louder, lower backpressure pipes, have experienced an increase in the rapid popping/gurgling noises when throttling back and gearing down. With less backpressure, the exhaust vapors tend to load up in the system, and ignition of these vapors is sporadic and annoying. This popping occurs further down in the pipes, and is louder because of more open baffles, or no baffles at all. The quick fix for this is to simply "plug up" the air tubes that go into the cylinder walls, thereby preventing the air from getting there in the first place, thus, no "in-the-pipe" ignition. You may still experience some occasional popping, set off by the intense heat, but it is much less frequent.

Removing or disabling the Pair Valve will have no ill effects whatsoever to the bike even if its is still stock. The pair valve system will likely clog with carbon after a year or so, and quit working anyway. Removal is simple, and will take less than an hour once you have all the "stuff" together.

The presence or absence of the Pair Valve does not affect your fuel mileage, power, or general engine running condition. It's purpose is solely to thin out the exhaust mixture so that it will pass all available emission control standards, and this "thinning out" occurs at the exhaust ports *after* the pistons and spark plugs have done their job.
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Subject: Re: Exhaust popping? Mon May 19, 2008 8:03 am

Yep.. Pair Valve on a bike. also called an airpump on a car. Ford Mustangs in Canada/US have the airpump idea. Totally ridiculous.. Car runs rich, wont pass emissions, so let pump some fresh air into the exhaust to fool the gov readers.. and the gov of course knows this.

We always tore the aipump out..
Just another fukn part that the car doesnt need, and likely makes the car companies more money, and us more fuckin headache.

As for the popping, yeah thats unburnt fuel / rich fuel, that is in the tail pipe and ignites part way down because you have let off on the throttle which slows the spark, but the valves are still letting in a bit more fuel.. so the unburnt portion ends up out the exhaust valves, and into your header, and then pop pop..

Somehow I think that Z's problem might not be this pretty innocuous one since the issue turned up all of a sudden, after a visit to a wrench.

Z did you notice a loss of power anywhere?
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P Plater Joined : 17 Apr 2008 Posts : 90 Location : Aus

[quote="RoNNo2WheelZ"]Totally ridiculous.. Car runs rich, wont pass emissions, so let pump some fresh air into the exhaust to fool the gov readers.. and the gov of course knows this.
[quote]

It makes sense to me mate. If you can get a much higher exhaust AFR before the vapors reach the cat-converter, it should help the cat-converters burn hotter and faster.

Pity I don't have a cat-converter. :pirat:
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Subject: Re: Exhaust popping? Mon May 19, 2008 8:17 am

Cats are ridiculous. hence. (most gov vehicles, incl military ones) in north am are catalytic exempt. Commercial vehicles can be sold w/o cats.. I know I bought a van back in the day that was from a commercial fleet.. no cat.. Not to mention that big industry that is loosely controlled regarding their emissions..
Catalytic, E-Testing, and all that... responsibility squarely placed on the shoulders of the consumer, when most of the pollution is produced by others.. while making it look like they are doing something about the environment, and letting us believe that we are guilty if we dont. More Rhodium, and Titanium that is sold on the metals market.. extra parts that fail and have to be replaced.. blah blah blah.

So I refer back to my original statement.. air pumps and the catalytics that need them are ridiculous! Hah! (well for performance anyway... I do believe that cats serve a purpose and have one on my daily driver in Canada.... but its high flow..)
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P Plater Joined : 17 Apr 2008 Posts : 90 Location : Aus

Good points mate.
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Subject: Re: Exhaust popping? Mon May 19, 2008 8:48 am

Subject: Re: Exhaust popping? Mon May 19, 2008 9:31 am

OK not only is it popping but the fumes smell worse than they've ever done before.....
Loss of power is on the lower end (i think) , but nothing great really.

Tks for the write up Tim and Ron.
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Zorgoth, the god of Zatheism

Subject: Re: Exhaust popping? Mon May 19, 2008 10:00 am

If the fuel smells a bit acidic.. that def means its running rich.. thats usually unburnt octane in the fuel.. Then again, running rich isnt that much of an issue.. except for fuel economy.
And as far as feeling like you lost some bottom end torque.. you lose some of that that everytime you you free up the airflow. Less backpressure means the engine can spool up faster, and hit better top end speeds.. .. airflow determines the speed of RPM in the engine..

Think of a garden hose.. water enters one end and exits the other much like the air in an enigine.

If you pinch off the end of the garden hose, you get less water, but its under more pressure and raring to get out.. So it seems like there is more water flying out due to the distance it will squirt. Unpinch the hose, and the water flows free, you get more volume but the flow is a lot more calm. ..

So on a bike. taking off the catalytic, or putting in a K&N filter, or changing your exhaust, putting in bigger valves will give you the sense and the reality of a freer flowing air situation in your bike.. that doesnt seem so torquey at the bottom end, but in reality is faster and better in top end..

BTW freer flowing air also means less turbulence, which also robs yoru engine of power, due to fuel being concentrated in patches in the mixture instead of beeing even.. more unburnt fuel, or rich spots that swirl around.. Further the turbulence can also impede the straight thru airflow on the engine which is key..

Think of the idea of going straight down the road or making circles in a few spots before going striaght again.. Straight is faster.. circles slow you down.. ..

My car experience.. I had a 1994 Chevy Camaro with the corvette LT1 engine in it back about 13 years ago (wow its been a long time!) and I bought this little tiny peice shaped like an H or 2 C's back to back. developed by a tuner named Lingenfelter. all I had to do was put this thing into my throttle body where the air entered the barrels, and it was supposed to calm turbulence. Well it did.. the car spooled up faster and I ended up shaving 2 10ths off my QT time. My skeptical buddies were pretty surprised at it as well!

Freer flowing air, means less turbulence, which means better air flow, which means gains in economy and horse power.. and better top end (and undetectable bottom end) acceleration.
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"All work and no play makes Jack a dull boy and Jill a rich widow." Evan Esar

Subject: Re: Exhaust popping? Mon May 19, 2008 10:08 am

Something else came to mind..
Did you get your plugs changed during the tune up at the wrench?
Cause if he put in a colder running spark plug, that could be the culprit right there.
Shd ask him what brand/model he used and then do some research on the plug and model.. Some use a colder plug because they have less fuel running thru the system, or due to emissions.. Hotter plugs will burn more fuel..
Could also be the gap.

Try the simple stuff first.. Plugs, / Injector.
Run an injector cleaner thru. take out a plug and see if there is blackness on the tips which indicates unburnt fuel and carbon deposits.. Usually means you need a hotter plug.

If the injectors are dirty, then the fuel will squirt out of them in a stream rather than a mist and that wont vaporize as fast.. and that means pockets of very rich fuel in your air flow.. also meaning that it wont all be combusted in the cylinder and some of that will fly out your exhaust ports and then detonate in your hot exhaust system.

So start cheap. and then work your way up to Dyno's and Power Commanders..
Plugs are cheap and injector cleaner is too
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"All work and no play makes Jack a dull boy and Jill a rich widow." Evan Esar