Nothing to worry about. Actually it's not that technical of a question haha. All that's happening is that there are some unburned HC's making it through your cat and burning once they come in contact with the tailpipe (which is what the popping is). Unfortunately, modern catalytic converters can't eliminate ALL of the unburned fuel that comes out of the exhaust. They're getting close, but not quite there yet.

When you put the Yosh pipe on, you took off the stock catalytic converter, so now there are more unburned HC's going to the tailpipe and "popping." It's normal. I think the popping sounds cool actually, but that's just me.

 

You need to add a fuel management system to your bike since you added a full exhaust.

Backfiring is not a good thing; you are dumping more fuel than the engine can efficiently burn.

 

I agree completely to the first statement. The second however, is only partially true. The engine will NEVER burn all of the fuel, and there will always be SOME unburned fuel coming out of the exhaust, which is why every vehicle comes from the factory with a catalytic converter, to separate the H from the C and add some O to make H2O, CO2, and CO. So, some of the "popping" noises due to the excess unburned fuel is okay. Too much of it is bad though, but from what you described, it doesn't sound like it's happening too much. Your A/F ratio should be adjusted to accommodate your new exhaust, though, because the stock fuel map was designed to work with the stock exhaust, not an aftermarket one. Even though, if there is a place for an O2 sensor in your new exhaust, in theory, the computer should automatically adjust the A/F ratio. Of course, this is only if you can put an O2 sensor in your new exhaust, and of course not everything works in real life as it does in theory.

 

had the same problem when I put my Taylor Made on just block off the pair valve. where the inlet is in the air box under the air cleaner. do a search there is a thread on it. presto problem solved. :thumbup:

 

You are correct...I missed that hahaha:thumbup: good call.

 

Thanks for the answer Mike. I wasn't worried, been around the race track enough to know it was normal. I just could figure out exactly what it was that did it.

Think is sounds great too.

Oh, and no worries Ultimate, I put a PC3 on the day I threw the exaust on (all done by my self, Im proud to say). And yeah I got it mapped. Wish I could get a coustom map, but there is no one out here that does it. I may be squiddy at times, but Im not that squiddy :thumbup:

Thanks much

 

Again thanks Mike, I was able to investigate futher now that I knew what the sorce is.

The technical term is "Afterfire" (like backfire, but... after) lol.

Does that Yosh pipe even have a cadalidic converter? Box said it wasn't street legal :hmmm:

 

Yeah no problem. Afterfires, that's good to know haha I never actually knew what that was called. I don't think the Yosh pipe has a cat, I think it's just two muffler canisters. No aftermarket exhaust that I know of has a cat now that I think about it. About your pipe being legal...bikes '06 and newer are required to have cats. Not to mention other emissions control systems. But we still don't have to smog our bikes yet, so they're not yet enforcing these rules...I wouldn't worry about it.

Also, just curious, did you plug in the stock O2 sensor into the Yosh exhaust? If not, that explains why you need to remap the computer when you throw a full system on.

 

Yeah hopefully when I get over to Germany they won't smog it there either.

I didn't plug any sensor into the exaust, no. There was a wire I had to pull, that diabled a sensor. The bike gives you an error code other wise. It was part of a system that operated this valve in the exaust pipe (located right before the muffler). It was kind of a butterfly valve, and all it did was hurt performance lol.

 

Oh okay. So the EXCV (exhaust control valve) threw a code when you removed it, but the O2 sensor didn't? Haha that's interesting...

And actually that valve doesn't really hurt performance, it just evens it out. It supplies more backpressure at the low RPMs so the low end torque isn't lost, and opens up completely at higher RPMs to decrease the backpressure, but still doesn't decrease it to the point where it would be if there weren't one there...if that makes sense. So, at higher RPMs you definitely would gain a little power without it, but in the lower RPMs you would lose out on some torque without it. Unless you re-tune the computer...which you have done, so you have nothing to worry about haha.

 

Block the PAIR line off at the Air box. The problem will go away. You should get a Fuel Management system as well but you probably won't cure the problem with that.

 

Block the PAIR line off at the Air box. The problem will go away. You should get a Fuel Management system as well but you probably won't cure the problem with that.

Sorry, see by your sig, you already have a PCIII for fuel management.

 

I don't understand how the back pressure helps with the lower revs. :hmmm:

what causes that?

 

...I know I already have a fuel management system. Im curious as to how back pressure would help in a situation were you dont have a computer or aftermarket exaust...

 

You're right haha it's to regulate sound actually.

 

You're right haha it's to regulate sound actually.

 

When you're at high rpm with full or partial throttle, your pcm tells the injectors to shoot fuel into the system accordingly, allowing the propor air/fuel ratio. (usually about 13.1:1. This is an ideal ratio. In a perfect world, if o2 levels didn't vary from location to location, then it would take 13.1 parts of air to completely burn 1 part of fuel. This is also why we have o2 sensors to adjust fuel flow to hold this ratio) When you snap the throttle shut, the fuel has usually already been injected into the cylinder that is on the power intake stroke. Since the throttle body(ies) are closed, there isn't much air being taken into that cylinder, thus decreasing the air fuel ratio. (anywhere from 4:1 to 10:1) Fuel needs air to burn, so some of that fuel isn't burned and is HOTTER than your mother on saturday night. (It's as hot as the fuel that has already combusted) So, once it tastes oxy...BOOM...

Watch MotoGP, see the flames out the exhausts?

Yeah

-HH

 

I didn't think the 07 and under had an O2 sensor. I thought they just got those in 08.

 

So the earlier years use speed density? There has to be some form of oxygen detection, or air meter for a fuel injection system. Whether it's on the intake or exhaust side.

On another note to a previous reply by who I don't remember...
If the popping noise was created because the motor consistantly has unburnt fuel, it wouldn't only pop when backing off throttle.
And you'd sound like a harley...

popopopopopopopopopop

 

On another note to a previous reply by who I don't remember...
If the popping noise was created because the motor consistantly has unburnt fuel, it wouldn't only pop when backing off throttle.
And you'd sound like a harley...

When opening the throttle, you're letting more air in before the computer adjusts the pulse width of the fuel injectors, this is called a lean shock. Once the computer adjusts and enriches the fuel mixture, if you let off the throttle the computer won't immediately compensate for the less air coming in, and you'll have an overly rich A/F ratio for a brief moment. This is where the unburnt fuel that causes the popping comes from, the overly rich mixture.

Generally, the normal amount of unburned fuel coming out of the exhaust isn't enough to create a combustible A/F ratio...it's too lean. There still is definitely unburned fuel coming out of the exhaust, but not enough to make any popping noises. When you let off the throttle and create the overly rich mixture for a brief moment, there's just enough unburnt fuel in the exhaust to create a combustible A/F ratio, and that's why you get a few pops when decelerating and not accelerating.

 

I've never actually looked on my bike, but according to the service manual for the K6-K7, there's a heated O2 sensor upstream of the EXCV.

 

YES! What you said ^ exactly. I guess I tried to over-explain it.