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Author Topic: Enlarged Airbox (and other Airbox Mods) for Carbed Monster  (Read 18513 times)
koko64
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« Reply #60 on: May 02, 2013, 12:43:49 AM »

Well the 900ie cams went in (thanks Rowan).
I put in a new sprag bearing, swapped the electric fuel pump for a Monster vacuum pump, tweaked the carbs and beefed up the starter wiring. The rebuilt starter works well without the electric pump drawing power. With only a 300W alternator the absence of an electric fuel pump helps not only starting, but keeping the Shorai battery topped up to 14Volts. It struggled to keep the Li battery at 13.5 Volts.

Bike starts great.

Curious to see how the big cams work with the big airbox. The owner is talking about another dyno run. He's also talking about porting.

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1999 M750.    "Scrambler"
2013 M1100 Evo    Street
2004 GSXR 750     Track
koko64
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« Reply #61 on: May 19, 2016, 02:02:16 PM »

Since this relates to a new thread and I had questions asked about this, I thought I'd raise this one from the dead rather than redo pics and info. This goes through the process in more detail of how to "enlarge" the airbox on your carbed 900. It's not really made bigger but rearranged in it's layout to increase the sub filter volume by about a litre and make all the box contribute. If your bike doesn't have porting then its a waste of time. I found the shortened rubber velocity stacks made airbox removal and replacement easier as did relocating the razor sharp filter support struts. Servicing was easier. The AFR for the shortened stacks showed a more stable graph for the 900 allowing bigger main jets to help WOT midrange without going crazy rich at high rpm. The opposite was true when I tested pod filters.

My conclusions and theories to explain the power gains may be better understood, explained and tested by others with a better theoretical framework. My majors were in the social sciences not engineering. I ran out of dyno money pretty quickly trying to learn stuff. It would be great if people test these mods to gain some repeatable data as I am down here in Oz and was testing with Oz fuel on local dynos, using a modified 900.
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1999 M750.    "Scrambler"
2013 M1100 Evo    Street
2004 GSXR 750     Track
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