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Discussion Starter · #1 · (Edited)
Just wondering if anyone out here has or had a similar issue. I have a K&N air filter and just installed a complete header back free flow shorty exhaust. No db killer just straight through pipes. Since then I have noticed only upon startup that the tachometer is loping a bit at idle. It seems to be searching for idle between 1400 and 1500rpms. The needle moves slightly up and down. If I give it a bit of throttle it usually takes care of it. Driving is fine, idling at stoplights or parking its fine..stays at a good 1400 +/- 50rpm. But if I turn it off and start it back up immediately it starts this searching again. I wouldn't call it a rough idle at all. Not noticeable unless looking directly at the tach. I'm pretty sure it is the 02 sensor and computer reading the amount of oxygen in the system. Just for the record, I can definitely rule out exhaust leaks at every point. I have thoroughly tested that already.
I know a remap would possibly help but it isn't that serious of an issue to me to spend money on a power commander and dyno time to fix it. Any thoughts?
 

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If the bike is other wise working well and doesn't "pop" on deceleration...I would not be concerned about it. However if you are like me and am anal about stuff well dig into it man...:)
 

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How quickly is it doing the hunting? Mine does that a bit (fairly slowly) when cold as it figures itself out and warms up eventually settling at it normal idle speed which I consider normal EFI behavior as part of the closed feedback loop.
 
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You need a proper slip-on muffler with a certain amount of back pressure.
 
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You need a proper slip-on muffler with a certain amount of back pressure.
The Danmoto systems I have seen on Youtube even with a baffle have been quite loud. So maybe there is not enough back pressure..
 

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Any straight pipe of about 2ft, is sufficient for back pressure.
It'll prevent unburned fuel from igniting close to the valves.
Back pressure only lowers performance.
However, most carburetor or fuel injection systems are tuned with the back pressure in mind.
Removing the back pressure may make the engine run more lean, and re-jetting, or re-fuel-mapping the fuel injection system might be necessary to make it run at it's optimal ratio.

It may be that the fuel injection system is noticing lean burn, and adds a bit of fuel, at which the rpms go up, and reduces the fuel to drop the RPM again.
All you really need is some way to reduce the air intake.
If it was a carburetor, adjusting the idle screw (connected to the throttle) would do.
Try seeing if adjusting the throttle cable somehow helps.
 

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All you really need is some way to reduce the air intake.
If it was a carburetor, adjusting the idle screw (connected to the throttle) would do.
Try seeing if adjusting the throttle cable somehow helps.
Adjusting the throttle position via cable adjustment will only change revs not fuel/air mixture. Same with a carbureted bike, adjusting the idle screw only changes the revs.
I don't think restricting the intake would help, the ECU would compensate for this.
My best guess is that it's due to lack of back pressure. Have suggested to Mikal about fitting a Db reducer to see if it helps.
 
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Discussion Starter · #8 · (Edited)
It's not really that bad just like UKCooper said I think it's normal feedback response. It doesn't even happen at the very first cold startup in the morning. It's after driving a while and stopping at a store, coming out and starting again. But I have figured out exactly what is causing it and how to stop it. Usually, when coming to a stop I downshift, downshift, engine brake and most times when parking I downshift into first. Doing so now makes a very loud crackle pop crackle. Not a backfire but a really nice sound lol..so I do it alot. Then I notice on startup it is searching a bit for a nice idle until I either ride it 10 feet or give it a couple blips of the throttle. But if when i come to a stop by just rolling in from 2nd and pull in the clutch, shift to neutral thus not creating the hotrodish crackle pop sound. Then it starts fine. So by doing the downshifting into first and letting it engine brake to almost a stall before pulling in the clutch, it must be sucking oxygen up into the system or a backpressure issue is all I can think, screwing up the O2 and computer. Then I turn it off so that when I turn it back on the computer has to kind of 'rethink' and adjust because its last memory was a bad one :)? Anyway, I figured out how to stop it, just not sure of the exact 'technical' term or reason.
 

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Discussion Starter · #9 ·
Adjusting the throttle position via cable adjustment will only change revs not fuel/air mixture. Same with a carbureted bike, adjusting the idle screw only changes the revs.
I don't think restricting the intake would help, the ECU would compensate for this.
My best guess is that it's due to lack of back pressure. Have suggested to Mikal about fitting a Db reducer to see if it helps.
Did order the DB Killer just to have on hand at least
 

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It is the bike trying to idle in closed loop mode. (This means it is trying to idle with fixed computer parameters and no inputs from the oxygen sensor). On startup you are in open loop mode. this means the computer can adjust the mixture to get the idle right (usually to cold start). Because the new exhaust the readings are going to be different from what the ecu is used to and because the bike is in closed loop mode it trys to make minor adjustments to where it thinks the bike should be without input from the oxygen sensor. In theory reseting the ecu can sometimes clear the problem but usually it will need a retune so the map can account for the new readings.

The reason people get away without remapping comes down to the design of the exhaust. A much higher flowing exhaust will give you a much happier high reving engine but will really mess with your low down rpm's usually resulting in a lose of torque and rough idle.

Exhausts like the 2brothers tarmac one are designed to have some back preassure still and give small gains through the entire rev range this means that because the readings only deviate a little from stock parameters the ecu in closed loop mode can handle the changes better.
 

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Discussion Starter · #11 · (Edited)
It is the bike trying to idle in closed loop mode. (This means it is trying to idle with fixed computer parameters and no inputs from the oxygen sensor). On startup you are in open loop mode. this means the computer can adjust the mixture to get the idle right (usually to cold start). Because the new exhaust the readings are going to be different from what the ecu is used to and because the bike is in closed loop mode it trys to make minor adjustments to where it thinks the bike should be without input from the oxygen sensor. In theory reseting the ecu can sometimes clear the problem but usually it will need a retune so the map can account for the new readings.

The reason people get away without remapping comes down to the design of the exhaust. A much higher flowing exhaust will give you a much happier high reving engine but will really mess with your low down rpm's usually resulting in a lose of torque and rough idle.

Exhausts like the 2brothers tarmac one are designed to have some back preassure still and give small gains through the entire rev range this means that because the readings only deviate a little from stock parameters the ecu in closed loop mode can handle the changes better.
Yah since the new exhaust (have a K&N air filter too) it soars through the higher revs 5500-9500rpms. It use to feel a little held back around 7000 and I use to shift about 8000. To me it felt like 8000 was about where I wanted to shift. But now it's at 9500 in a blink. It doesn't have a 'rough' idle at all tho. Only when starting it...the tach goes from 1400ish to 1500 till i blip the throttle a couple times or drive it a few feet then it idles perfect. I'm really not concerned about it as I know it's caused from the lack of backpressure, also it's gains far outweigh that little issue. When installing the pipes I did unplug the battery since I was removing the 02 sensor and the ground wire attached to the pipe. After the first ride I figured I'd better unplug it again to reset the ecu. I unplugged it for about 30 minutes. I read somewhere that it should be for about an hour. You think that really matters? After a few days I would think the ecu would learn itself. The narrow band O2 really only works in the very low rpms right? Once it gets to a certain rpm it doesn't care what the O2 readings are? I've been looking at different controllers, dynojet, magnum, and bazzaz. I've been talking to a bazzaz tech and he sent me a dyno for a map with a K&N and a 2 Brothers and it wasn't even worth any gains for the $350 price. Torque and HP were only about .60 increase. I'll just let it be, honestly it's performing the best it ever has since I bought it
 

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Again good review/write up. Now have you lost lowend torque with your new pipe? Does it "stumble" in the higher gears as you accelerate?
 

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Discussion Starter · #13 ·
Again good review/write up. Now have you lost lowend torque with your new pipe? Does it "stumble" in the higher gears as you accelerate?
I don't notice any loss of torque. No stumble at all its completely smooth. Before it would get up to around 7000rpms and it kind of felt like i was pushing it to get up to 9000...it felt constricted. Now the needle just goes straight up to 9500 and I shift into 2nd and yes it does pop the front tire up a bit. lol. No clue if others do this too? I've just noticed it now. Not sure if this has any effect at all but I also have the rear shock set to the 5th position so its pretty stiff.
Like I said overall it feels like a different bike since I got it and it was bone stock.
 

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So do you think you really need the baffle?
 

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When I fitted the LV pipe on my old 250R I didnt think I had lost any torque, but when I put the original pipe back on for re-sale I really noticed the difference straight away.
I didnt have any wandering idle issues with it tho.
 
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Yah since the new exhaust (have a K&N air filter too) it soars through the higher revs 5500-9500rpms. It use to feel a little held back around 7000 and I use to shift about 8000. To me it felt like 8000 was about where I wanted to shift. But now it's at 9500 in a blink. It doesn't have a 'rough' idle at all tho. Only when starting it...the tach goes from 1400ish to 1500 till i blip the throttle a couple times or drive it a few feet then it idles perfect. I'm really not concerned about it as I know it's caused from the lack of backpressure, also it's gains far outweigh that little issue. When installing the pipes I did unplug the battery since I was removing the 02 sensor and the ground wire attached to the pipe. After the first ride I figured I'd better unplug it again to reset the ecu. I unplugged it for about 30 minutes. I read somewhere that it should be for about an hour. You think that really matters? After a few days I would think the ecu would learn itself. The narrow band O2 really only works in the very low rpms right? Once it gets to a certain rpm it doesn't care what the O2 readings are? I've been looking at different controllers, dynojet, magnum, and bazzaz. I've been talking to a bazzaz tech and he sent me a dyno for a map with a K&N and a 2 Brothers and it wasn't even worth any gains for the $350 price. Torque and HP were only about .60 increase. I'll just let it be, honestly it's performing the best it ever has since I bought it
yeah at WOT (wide open throttle) computer just ignores all sensors pretty much and just goes max everything.people who actually use loud high flowing racing exhausts for actual racing dont mind the loss of torque at low rpm because they really dont spend any time there during a race
 

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yeah at WOT (wide open throttle) computer just ignores all sensors pretty much and just goes max everything.people who actually use loud high flowing racing exhausts for actual racing dont mind the loss of torque at low rpm because they really dont spend any time there during a race
So, a question is then, how do we know which aftermarket exhaust will kill low/mid torque? It's not like manufacturers state it in the description. I often see "tested at dyno for optimum peformance throughout the torque range". Or, do you consider racing exhaust the ones without the baffles? :serious:
 

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The easiest way (or really the only way) without physically testing in person is to see a dyno performance sheet and look at where the gains are. Unfortunately most exhaust companies don't offer dyno reports and some have even copied and pasted theirs from other manufacturers sheets. dyno sheets that have larger gains in the higher rpm to me indicate a louder free flowing exhaust. These sheets almost always show a lose down low (I even see dyno sheets that don't start till a higher rpm so that they don't have to show you the loose). Dyno sheets that show small gains across the whole rev range will be slightly louder than stock and wont have the top end a highflow exhaust will. These will also mess with the factory ecu settings alot less. Unfortunately this type of exhaust takes a lot more R&D to develop and this is usually reflected in the cost of the exhaust. If anything remember this "Getting a high flow exhaust and slapping a db killer in will not give the same result as a slower flowing quieter exhaust". Picking an exhaust is always a compromise and you should work out the end goal for the bike long before you purchase it.
 

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Discussion Starter · #20 · (Edited)
When I fitted the LV pipe on my old 250R I didnt think I had lost any torque, but when I put the original pipe back on for re-sale I really noticed the difference straight away.
I didnt have any wandering idle issues with it tho.
I don't feel any loss of torque as you say. But if I was to put the stock exhaust back on I'm sure I would. Negligible tho. The free flowing feeling and the rpm guage shooting up to 9500rpms so fast n smooth makes up for any torque loss of 1 or 2ft/lbs? I always felt first was so low that any loss of torque there didn't matter to me. Now that I've seen the top end open up..over 6000rpms I wouldn't go back to anything that wasn't 'open' or as some say racing exhaust.
 
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