Newbie here....fueling question with aftermarket exhaust - - Excellence in Motion
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post #1 of 2 (permalink) Old Jun 18th, 2013, 2:19 pm Thread Starter
Tom07K1200GT's Avatar
Join Date: Jun 2013
Location: Indianapolis, Indiana, USA
Posts: 54
Newbie here....fueling question with aftermarket exhaust

I'm sure this has been gone over here before, but my quickie search turned up a ton of other conversations besides what I was looking for.

All I am after is the answer to this question:

When installing an aftermarket exhaust (either slip-on or full exhaust), does the ECU need to be reflashed with a different tune (dependent upon which exhaust option you choose of course) for fueling purposes?

The reason I ask is that I just rode my new purchase home on Friday last week from Austin, TX and it seems to have a bit of a stumble when I get on the throttle, almost like a rich fuel condition. I have no proof it's running rich other than the end of the Remus can is a bit discolored from the carbon.

Many thanks in advance for any input or slashings because I've asked the same question that tons of other have asked in the past.

2007 K1200GT
Dark Graphite Metallic
Bought it with 2,055 miles on the clock - June 2013
Rode 1,100+ miles to get it home
Current miles: 10,350+
Xenon, Remus Hexacone slip-on
BMW small top box (that now likes to fly away on it's own) with pad for the lady

Other Toys
1987 Buick Grand National
2007 Trailblazer SS
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post #2 of 2 (permalink) Old Jun 18th, 2013, 8:44 pm
Join Date: May 2009
Location: , TX, USA
Posts: 752
The ECU will adjust the closed-loop A/F ratio automatically, within limits, and the open loop map should be close enough unless you made a radical change. But be aware that fueling is only one thing that is affected by an aftermarket exhaust. Cam timing, ignition advance curve, etc. are set up expecting an OEM system so any major changes to intake or exhaust can easily lose more power than they gain, and without a re-tune that is frequently what happens, or power is shoved around a bit withing the powerband so you may have a net increase at one engine speed and a loss a net loss at another. Which was best, before or after? Anyone's guess unless engine performance is addressed as a system since there is no guarantee that changing a single component to a 'performance' version will do very much unless the OEM design was significantly lacking, and this usually isn't the case with BMW bikes. The slant-K bikes in particular are tuned pretty highly just as they come from the factory.

Anyway, to your situation, since the OEM maps are on the lean side to meet emissions regulations then reducing backpressure can serve to make that condition worse. You may have a lean stumble, not a rich condition. If that is the case one of the preset fuel enrichening devices might help (kind of a shotgun cure), or better option would be to install a Power Commander and have the open-loop map properly tuned on a dyno. All-in-all a PITA for a maybe few more hp a high rpm, which is all you're going to get even under the best conditions.
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