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Old 04-23-2007, 03:51 AM   #1 (permalink)
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Default Slip-Ons and Rejetting...

Hey everyone.

Settle an argument for a friend and I.

We're discussing motorcycles and slip on mufflers.

He says that you don't have to worry about re-jetting the carbs because the slip on is just a bolt on replacement for the stock muffler.

I say that I've always been told that whenever you do anything to the exhaust on a bike you should have the jets adjusted accordingly.

So, is it absolutely necessary to rejet after replacing a stock muffler with a slip-on, or is it only necessary when going with a completely different exhaust system??

Thanks.
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Old 04-23-2007, 06:42 AM   #2 (permalink)
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Slip on's are pointless. They are just for looks and sound. You would want to rejet with a full exhaust.
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Old 04-23-2007, 06:48 AM   #3 (permalink)
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Most engines will require and increase in intake/air/fuel flow after you have increased exhaust flow (after adding a can).

However, some cans (like D&D out of texas, which included a new mid pipe) dont make a jet change mandatory. I called the factory myself and was told that a jet change was completely unneccessary as long as the can was the only mod.

However after modding my airbox and adding a low restriction air filter I rejetted accordingly.

Most mechanics will tell you that the new bikes are so lean from the factory that any change that makes them leaner (like adding exhaust flow without more intake/air/fuel flow) will leave a potential to hurt the bike buy running too lean.
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Old 04-23-2007, 06:57 AM   #4 (permalink)
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This is EASY to answer!

To start off, each bike is different and every exhaust system is different. SOME exhaust systems don't require you to rejet or remap the bikes fuel delivery because the difference in performance gains throughout rpm ranges is not significant enough to require more or less fuel / air.

Example 1: I had a yoshimura slip-on pipe on my 2000 gsxr600 (carb'd).... with stock air filter... and I did NOT remap or get a power commander, or rejet it... the bike ran great and did not run too rich.

Example 2: My friend has a micron slip-on pipe on his 2005 gsxr600 (fuel injected).... with stock air filter...and he does NEED to remap or get a power commander because his bike is running very rich.

There is always performance to be gained by adding a power commander even with a slip-on pipe (with or without an aftermarket airfilter).... the gains might not be as significant with a slip-on pipe as they would be with a full exhaust, but to me a gain in performance is a gain in performance.

There are a few exhaust systems that SUPPOSEDLY don't require you to need a power commander / remap / rejet..... but look at that statement.....YOU ARE NOT REQUIRED to have a power commander and etc...

My opinion: No it's not necessary with ALL slip-ons. Yes it helps and IS necessary for some slip-ons. It is also always necessary for full exhaust systems.

Hope that helps..
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Old 04-23-2007, 07:22 AM   #5 (permalink)
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Quote:
Originally Posted by lownuff
This is EASY to answer!

To start off, each bike is different and every exhaust system is different. SOME exhaust systems don't require you to rejet or remap the bikes fuel delivery because the difference in performance gains throughout rpm ranges is not significant enough to require more or less fuel / air.

Example 1: I had a yoshimura slip-on pipe on my 2000 gsxr600 (carb'd).... with stock air filter... and I did NOT remap or get a power commander, or rejet it... the bike ran great and did not run too rich.

Example 2: My friend has a micron slip-on pipe on his 2005 gsxr600 (fuel injected).... with stock air filter...and he does NEED to remap or get a power commander because his bike is running very rich.

There is always performance to be gained by adding a power commander even with a slip-on pipe (with or without an aftermarket airfilter).... the gains might not be as significant with a slip-on pipe as they would be with a full exhaust, but to me a gain in performance is a gain in performance.

There are a few exhaust systems that SUPPOSEDLY don't require you to need a power commander / remap / rejet..... but look at that statement.....YOU ARE NOT REQUIRED to have a power commander and etc...

My opinion: No it's not necessary with ALL slip-ons. Yes it helps and IS necessary for some slip-ons. It is also always necessary for full exhaust systems.

Hope that helps..

if your friends gsx-r was running rich, wouldn't a more free flowing exhaust make it run leaner? I guess my point is he would have been running rich from the factory and a slip-on wouldn't have affected that but if anything it would have leaned it out a bit due to less restriction. Just a thought.

Nate
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Old 04-23-2007, 07:26 AM   #6 (permalink)
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Quote:
Originally Posted by lownuff
Example 1: I had a yoshimura slip-on pipe on my 2000 gsxr600 (carb'd).... with stock air filter... and I did NOT remap or get a power commander, or rejet it... the bike ran great and did not run too rich.
remapping/ adding a powercommander is something you do to adjust the FUEL INJECTION. carbed bikes require rejetting.
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Old 04-23-2007, 07:32 AM   #7 (permalink)
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I just put a Scorpion bolt on my bike, it runs great and does not backfire, but it kind of grumbles and "pops", when downshifting a little? Sounds cool I think..

I wonder if a PC would help eliminate that and improve fueling...?
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Old 04-23-2007, 10:07 AM   #8 (permalink)
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Quote:
Originally Posted by lownuff
This is EASY to answer!

To start off, each bike is different and every exhaust system is different. SOME exhaust systems don't require you to rejet or remap the bikes fuel delivery because the difference in performance gains throughout rpm ranges is not significant enough to require more or less fuel / air.

Example 1: I had a yoshimura slip-on pipe on my 2000 gsxr600 (carb'd).... with stock air filter... and I did NOT remap or get a power commander, or rejet it... the bike ran great and did not run too rich.

Example 2: My friend has a micron slip-on pipe on his 2005 gsxr600 (fuel injected).... with stock air filter...and he does NEED to remap or get a power commander because his bike is running very rich.

There is always performance to be gained by adding a power commander even with a slip-on pipe (with or without an aftermarket airfilter).... the gains might not be as significant with a slip-on pipe as they would be with a full exhaust, but to me a gain in performance is a gain in performance.

There are a few exhaust systems that SUPPOSEDLY don't require you to need a power commander / remap / rejet..... but look at that statement.....YOU ARE NOT REQUIRED to have a power commander and etc...

My opinion: No it's not necessary with ALL slip-ons. Yes it helps and IS necessary for some slip-ons. It is also always necessary for full exhaust systems.

Hope that helps..
The only way you are going to know if you bike needs rejeted/remapped for sure is to put it on a dyno with a Wideband.

If your friends bike is running rich after a slip-on, it was running WAY rich before the slip-on.
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Old 04-23-2007, 11:41 AM   #9 (permalink)
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Quote:
Originally Posted by vegasbound
I just put a Scorpion bolt on my bike, it runs great and does not backfire, but it kind of grumbles and "pops", when downshifting a little? Sounds cool I think..

I wonder if a PC would help eliminate that and improve fueling...?
Yes, a PC would help.

All bikes come lean from the factory to meet emissions (especially in CA, but it's easy to "fix"). Re-jetting a stock bike will usually help the throttle response. Adding a slip-on reduces exhaust back-pressure causing an even leaner condition. Is re-jetting required? Maybe not, but most bikes will run better if you do.
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Old 04-23-2007, 01:03 PM   #10 (permalink)
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+1

Even stock bikes will benefit from rejetting/FI tuning. They all run lean from the factory. Slip-ons will usually make you run a little more lean.

You probably can get away without rejetting/FI tuning with your slip-on, but it would help make the bike run a little better.
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Old 04-23-2007, 03:07 PM   #11 (permalink)
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Quote:
Originally Posted by g34343greg
remapping/ adding a powercommander is something you do to adjust the FUEL INJECTION. carbed bikes require rejetting.
glad someone said it....



as stated, not necessary.....
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Old 04-23-2007, 05:25 PM   #12 (permalink)
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Wow people on here need to understand FI and carbs before they start posting.


But in most cases, if JUST a slip-on is installed, then one will NOT have to rejet/remap the bike. But this depends on climate and altitude and other factors. But mostly NO.

Now, if you add an aftermarket filter, or do any other thing to allow a little more air flow then you should rejet/remap.
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Old 04-23-2007, 11:28 PM   #13 (permalink)
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Quote:
Originally Posted by g34343greg
remapping/ adding a powercommander is something you do to adjust the FUEL INJECTION. carbed bikes require rejetting.
Yeah I know.....

I said I didnt have to remap / rejet/ anything.

Just explaining that I didnt need to do anything with that bike, well aware that a carb bike would require jets to correct fuel delivery .... being as how they don't have fuel injectors...........thanx anyway.

Last edited by lownuff; 04-23-2007 at 11:31 PM.
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Old 04-23-2007, 11:30 PM   #14 (permalink)
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Quote:
Originally Posted by lemosley01
The only way you are going to know if you bike needs rejeted/remapped for sure is to put it on a dyno with a Wideband.

If your friends bike is running rich after a slip-on, it was running WAY rich before the slip-on.
Can't really explain it... his bike ran PERFECT before the pipe. Soon as he put the exhaust on, i swear to you the bike runs rich (or seemingly so).

You can smell it, and see it.

Anyway, like I said before...... it depends on the bike, and the exhaust system. Scorpion claims you don't need to do anything, but I can tell you it helps drastically.

Other exhausts require it. Contact the manufacturer of your exhaust, see what they recommend. Put it on, see how it runs. you decide.

Last edited by lownuff; 04-23-2007 at 11:32 PM.
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