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Author Topic: Running Rough at Idle After Installing Stock Exhaust  (Read 794 times)

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Offline Pete_in_AK

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Running Rough at Idle After Installing Stock Exhaust
« on: June 01, 2020, 01:52:15 pm »
OK guys I'm going to say straight up that I'm really, really new to motorcycles.  This is the first one that I've ever owned and in fact I just learned to ride this spring.  So I might ask some stupid questions or leave out some important stuff. 

I bought my bike used from the Harley dealership in Anchorage.  It had a megaphone-style exhaust installed that I absolutely hated.  But I loved everything else about the bike so I got it anyways.  I thought that I would just buy a stock exhaust off the internet and be good to go.

When the stock one came in the mail, it did not have a new gasket or a clip.  But I was excited about trying to install it and see what it sounded like, and so went for it anyways.  Got it installed, it sounded beautiful to me.  I ordered a new gasket and clip, and decided to just ride it as-is until the new one arrived.  The bike rode amazing and idled smooth as butter.  I've been riding it daily for about two weeks.

New parts arrived, I installed them on Sunday.  I took the bike for a ride afterwards and noticed that it was running very rough at idle when at a traffic stop.  Like rough enough to where it almost dies, I have to rev it a little to keep it going.  Also it backfires a little bit on deceleration now.  I'm thinking it has something to do with the new gasket and clip since that's the only thing I changed, but I can't imagine why that would do it.

The guy who owned it before me put a couple of other mods on there - a different air filter, and some kind of unit that attaches to the O2 sensor.  I apologize but I don't know what brand that thing is, it's just a little black box.  About that thing - I noticed that when I first turn on the ignition key it flashes really quick for about 20 or 30 seconds, then once the bikes been idling for a little bit it goes to a steady light.  I'm colorblind so I have no idea what color it is but I've included a pic.

Sorry for the long post but like I said I'm new to motorcycles and don't know what you all think is important.  My question is - should I take this thing back to the dealer and have them look at the mod (whatever it is)?  Should I just disconnect it altogether and replace it with a stock O2 sensor?


2015 Bolt C Spec

Offline 7udro

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #1 on: June 01, 2020, 02:52:11 pm »
you can install any exhaust to this bike and keep the rest stock..

but if you install a direct intake or a supercharger airbox you MUST reflash (to a proper map) or cheat the stock ecu with an aftermarket one


stock muffler is the main exhaust choke actually.


reinstall the other


and don't buy used bikes  ;D

Offline Pete_in_AK

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #2 on: June 01, 2020, 03:07:46 pm »
but if you install a direct intake or a supercharger airbox you MUST reflash (to a proper map) or cheat the stock ecu with an aftermarket one

Do you think that's what that box is?  Like I said, new to bikes so I'm not sure what you mean about "reflash to a proper map".  Is that something they can do at the dealer? 

reinstall the other


and don't buy used bikes  ;D

Resinstall the other - like the megaphone?  Not going to happen.  :)  I have no interest in being 'that guy'.  Also I bought it used because I can't afford a new bike. 
2015 Bolt C Spec

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Offline DrM

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #3 on: June 01, 2020, 03:14:00 pm »
(snip) you MUST reflash (to a proper map) or cheat the stock ecu with an aftermarket one

I have aftermarket slip-on (Cobra) and air cleaner (also Cobra) and I don't have an aftermarket ECU, fuel controller, or flash -- and the bike runs just fine - just like I like it.

That being said, you very likely do need a tight gasket on the muffler, else the O2 sensor will be picking up additional O2 sensing from air leaking into it.
 Just a thought, but reverting back to stock muffler likely means that you no longer need the black box, and likely should go back to the stock air cleaner and stock ECU (if it is not on the bike.)

Offline Pete_in_AK

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #4 on: June 01, 2020, 03:27:39 pm »
Just a thought, but reverting back to stock muffler likely means that you no longer need the black box, and likely should go back to the stock air cleaner and stock ECU (if it is not on the bike.)

Thanks for the suggestion DrM.  I've actually thought about this...I can get a stock O2 sensor online and try and just run that from the muffler to the bike.  Although I suppose I probably will still need to flash it if the previous owner modded that somehow.  GD it but I hate mods.  Always have.
2015 Bolt C Spec

Offline Sdaniels

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #5 on: June 01, 2020, 03:41:28 pm »
Pete, I've got an O2 sensor collecting dust.  Message me your address.
2015 C-spec

Offline 7udro

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #6 on: June 01, 2020, 03:56:00 pm »
get the 02 sensor


btw that rough idle could be intentional, someone like it like that because it's coooooool


so you can also keep it like that, maybe try to just  raise bike's minimum, it should be a screw


everything in the name of don't waste money

Offline Sdaniels

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #7 on: June 02, 2020, 04:20:22 pm »
That exhaust kind of looks like a Bassani or a Baron slash cut...you could make some money off that. 
2015 C-spec

Offline bedheadjulian

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #8 on: June 02, 2020, 05:16:04 pm »
It's surprising that the stock exhaust is causing such a problem. It isn't very restrictive compared to most OEM mufflers. You could try drilling out the main baffle though. (Use the search function to find out more)  It's a cheap and easy solution you could try out. The other thing to check is the back of the ECU. Many companies will put a sticker on it if they've "flashed" it. It's under the seat strapped onto the battery housing. Otherwise you could just buy a cheap slip-on muffler... EMGO makes a "tunable" reverse cone muffler that I put on my bike. I like the sound, not too loud with the "mechanical baffle" installed.  Whole thing ran me less than $120.
Hope this helps,
- J
« Last Edit: June 02, 2020, 05:19:08 pm by bedheadjulian »

Offline Pete_in_AK

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #9 on: June 04, 2020, 12:22:44 pm »
That exhaust kind of looks like a Bassani or a Baron slash cut...you could make some money off that.

That would be crazy!  Like I said in my original post, I'm really new to bikes but I can't imagine that thing cost much $$.  It truly is just a pipe with a threaded socket for the O2 sensor.  There are like no baffles or ridges of any kind whatsoever inside of it.

Head's up for everybody - thanks again for all your advice.  With no changes from me the bike has been running perfectly for the past few days.  So I'm going to chalk it up to some bad gas since I can't think of any other reason it would come and go like that.  I'm new to motorcycles but not engines and that's the only time I've seen sputtering like that just stop.  Unless you guys have any other ideas?
2015 Bolt C Spec

Offline Sdaniels

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #10 on: June 04, 2020, 12:51:53 pm »
Previous owner must have removed the baffle...yeah, I'd not want to ride that for any length of time either.  No markings/stamps on it?
2015 C-spec

Offline Pete_in_AK

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #11 on: June 05, 2020, 01:26:20 pm »
Previous owner must have removed the baffle...yeah, I'd not want to ride that for any length of time either.  No markings/stamps on it?

No, I actually just double-checked it this morning outside in the sunlight in case it was there, but faint.  Nothing at all.  Looks like it was made in someone's personal shop to be totally honest.  Not that it looks like crap or anything, but there is nothing that looks to me like it was made professionally.
2015 Bolt C Spec

Offline lunkhead

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Re: Running Rough at Idle After Installing Stock Exhaust
« Reply #12 on: June 05, 2020, 01:43:00 pm »
Quote from: Pete_in_AK
Looks like it was made in someone's personal shop to be totally honest.  Not that it looks like crap or anything, but there is nothing that looks to me like it was made professionally.

Then it's definitely a Barons. The O2 sensor is even in the wrong place.

Craftmanship aside, there's nothing good about the Barons.
« Last Edit: June 05, 2020, 01:52:50 pm by lunkhead »
C-SPƎC