"Running Lean" ?
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Joined: Aug 2011
Posts: 50
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From: Delaware
"Running Lean" ?
So I am about to install a set of Cycle Shack slip ons with 3" cut on my 2011 Nightster. I did a little research on this forum and it doesn't need like I will need to remap it, unless I find it "running lean."
So what exactly does "running lean" mean? What should I be looking/listening for in order to decide if I need to remap?
So what exactly does "running lean" mean? What should I be looking/listening for in order to decide if I need to remap?
Elite HDF Member
Joined: Feb 2008
Posts: 3,817
Likes: 2
From: Novi MI
New motorcycles are tuned to meet EPA emission regulations and the fuel mix is lean. The bikes with catalytic converters, your's has one, do run much better than the detuned bikes of a few years ago. Retuning the bike to run at it's best, called stage 1, makes them no longer EPA compliant.
Last edited by barjbar; Nov 1, 2011 at 10:26 AM.
Road Captain
Joined: Jul 2007
Posts: 552
Likes: 1
From: las vegas nv
Running lean
Lean refers to the air to fuel ratio mixture that is sent to the cylinder to be fired. I believe the usual a/f ratio is 13.7 parts air to 1 of fuel. So if you increase the amount of air for the same amount of fuel it is considered a "lean" mixture. Conversely, if increase the amount of fuel for same amount of air it becomes a "rich" mixture. Changing the pipes has no effect on the air or fuel coming into the engine so they do not effect a lean or rich mixture. So no a remap would be a waste of money. Your bikes ECM will detect any changes and will retune itself. There is a limit to the adjustments, and when you do an air filter change that is when the talk of a fuel management system comes in. Which is a whole different topic.
Also, as you asked some signs of a lean mixture are bluing of the pipes, especially of the rear cylinder, increases in heat from the engine and the pipes and generally some pinging of the engine upon acceleration. There are probably others but these are the most noticable. Hopes this helps, didn't mean to be so long. Take care, and ride safe.
Also, as you asked some signs of a lean mixture are bluing of the pipes, especially of the rear cylinder, increases in heat from the engine and the pipes and generally some pinging of the engine upon acceleration. There are probably others but these are the most noticable. Hopes this helps, didn't mean to be so long. Take care, and ride safe.
Seasoned HDF Member
Joined: Feb 2010
Posts: 5,618
Likes: 5,182
From: Green Country
I think it's worth mentioning that when an EFI bike is modified with an improved airflow filter and a performance exhaust system, the EFI fuel map needs to be modified to compensate for the increased air getting into the engine. Slip-on mufflers, conventional 2-2 and 2-1 exhaust systems all allow more air into the engine by reducing the exhaust restriction but they do not significantly alter the pressure waves in the exhaust system similar to drag pipes.
Road Captain
Joined: Jul 2007
Posts: 552
Likes: 1
From: las vegas nv
lean
hdgzr, the point I was making was that as the poster said he was only changing the mufflers. A hd reflash of the ecm will do him no good, for two reasons. One the hd reflash only recognizes hd parts. It will not recognize rush, v&h or any other brands. So you can not get an exact map but a "close" one. Two it does not change the a/f but simply raises the rev limiter. So in the case of just pipes it is a waste of money. And as i said change the air filter, that's a different story.
Seasoned HDF Member
Joined: Feb 2010
Posts: 5,618
Likes: 5,182
From: Green Country
And you are correct sir. A less restrictive muffler can allow more air back into the engine, although in amounts that the stock ecm should be able to handle. As mentioned, he should be just fine with slip-ons.
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Big Kahuna HDF Member
Joined: Feb 2006
Posts: 23,881
Likes: 34
From: USA
KB lean quick test: After you install the slip ons, take the bike for a 30 minute ride until nice and warmed up. Then run up to 5500 rpm in second gear and back off allowing the engine to wind all the way down to 1500 or just above idle speed. (make sure there are no cars behind you). If the engine pops like crazy (more than 2 times) out of the exhaust you are probably running too lean.If it just gurgles...no problem.
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