Test & tune went well.  On the initial ride the bike felt very good.  It started right up, no enricher needed, and settled into a nice idle.  I drove straight off with no hiccups, surging, or afterfire.  Roll-ons on the surface streets around my house were smooth and strong.  A quick run up the freeway to the next exit went well but at speeds above 55 it felt a little light on fuel.  Seat-o-the-pants test but it felt light on fuel by my standards.

Changed main jet from 145 to 147.5.  Went for a long freeway ride into Honolulu.  Strong headwinds made the little single work for it's dinner.  The entire round trip included long downhill freeway grades, long uphill freeway grades, city streets, stop & go, and suburban surface streets.  Carburetion felt spot on for the entire trip (about 1 hour total).  Very good power on surface street roll-ons from about 20 mph and up, 3rd & 4th gear.  Decent passing power on freeway.  No hesitation or flat spots.  Noise level equal to stock under all but WOT conditions.  WOT up hill may be slightly louder than stock but hard to tell with wind noise and helmet.  Not a hint of ping or knock.  Only one afterfire on the entire trip and that was when the engine was in warm-up mode.

I am satisfied with the results.

BTW, I had already gone through the carb prior to the airbox testing & mod.  I think if this airbox had been used with a bone stock carburetor it would have probably run pretty ragged .  The low speed circuits on the stock carb setup are so lean that the additional air would have made things worse.  Best as I can tell, most everyone on this forum has or is planning to go through their carb.  These mods work good with a properly setup stock carb.  I intend to do a separate post on my stock carb modifications.  They're slightly different from what I have seen here on the forum so I hope you find it interesting.  

 Is "bone" stock the same as stock?

Regarding Eegore's question about "bone stock" vs "stock".  My use of the term "bone stock" means the airbox was completely stock with an OEM air filter element.  I would consider an airbox with a direct replacement filter element as "stock" since it doesn't have an OEM element but rather has a direct replacement, supposedly equivalent to the OEM element.  I would consider an airbox with a K&N element to be "modified" since the K&N is a performance element superior to the OEM element.

D B M ,guess your right about the orientation ,wasn't aware ,I moved mine years ago along with the stock seat and rear fender.

I’m unearthing this old post because I want to try testing the airbox with my budget flow bench.  The simple manometer readings indicate improvements, but the readings don’t really quantify the improvements.  In other words, the simple manometer readings may show that a configuration is better, but better could be anything from 1 CFM to 50 CFM.  That’s because there’s no way to correlate a 1” H2O change to CFM.  Using the flow bench with the inclined manometer and orifice will allow an estimate of actual flow and will also permit comparison in percent of flow from one configuration to another.
 
If I can achieve a test pressure of at least 5” H2O, I will be able to use the flow bench conversion tables to convert to anticipated flow at other test pressures.  If I can’t achieve at least 5” H2O test pressure, then at least each configuration can be tested at the same pressure, and the data will be expressed in %, which IMO is more meaningful.

Fast 650 shared a formula for estimating maximum horsepower potential based on flow through the intake tract at 10” H2O.  I found the same formula in one of my old books.  The formula is .43 x (cfm at 10” test pressure).  The cfm value is obtained from a complete intake system (head, manifold, carb and air cleaner assembly).  So, if you want to build an engine with a target HP of 45, you need about 105 cfm through the entire intake system.  To achieve that much flow, I assume the air filter assembly (airbox, filter, connector hose, etc.) must flow at least 105 cfm.   Since their will be compounding losses of differential pressure as the air travels downstream through the carburetor, port, and valves, the airbox probably should flow more than 105 cfm @ 10” H2O.  Having the capacity to flow more than 105 cfm at 10” H20 will maintain the highest differential possible across the downstream components.
 
You must start somewhere, and that starting place is the airbox.  All the tests were performed with a 209-cfm orifice.
 
Here’s a shot of the budget bench installed on the bike.

Everything fit nicely, and the hookup was a breeze.

The modifications and testing I previously did examine various combinations and their associated drop in U-Tube manometer vacuum.  I reviewed all the various configurations and decided I would test five.  Based on the intended application, I consider these five combinations to be typical choices.  For the flow tests, I only had two elements, stock & K&N.  I don’t have a spare filter frame to use with the poly-fil material.  If I acquire a frame later, I will test with the poly-fil filter media and post the results. I gave each combination a name meant to be descriptive of the application.  The prior entries to this post provide pictures and details of the various mods.

Stock Configuration

Stock configuration is all the components of the airbox assembly exactly as delivered by the OEM except for the air filter element.  

Street Modified – Quiet

1.75” hole in the airbox cover, the baffle in the airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the decorative tin installed over the airbox cover, and either filter (Stock or K&N).

Street Modified – Semi Quiet

1.75” hole in the airbox cover, no baffle, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, the decorative tin installed over the airbox cover, and either filter (Stock or K&N).

Street Modified – Maximum

no airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, the decorative tin installed over the airbox opening, and either filter (stock or K&N).

Maximum Modified

no airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, no decorative tin installed, and either filter (stock or K&N).

You can see from the test data that even with the stock airbox, the 105 cfm threshold for 45 horsepower can be exceeded.  It appears as if downstream losses like the carburetor, intake port, and valves will be the limiting factor.  But using real world experience, most of us know that even with a stock engine, modifications to the airbox yield substantial improvements in performance.  You can feel the improvement.  So there is obviously more to it than meets the eye.

It looks to me like it’s a compounding problem.  The airbox drops the pressure as the air flows through, which then reduces the differential across the carburetor, which then drops the pressure as the air flows through, and so on.  Ultimately, the test needs to be performed with all the major players connected (airbox, carburetor and cylinder head).

You also see that if the stock airbox becomes the limiting factor, it would be very easy to modify the airbox to achieve large improvements in flow.  Using the stock filter, flow can be improved about 41 cfm.  If the K&N is installed, it looks like flow could be improved at least 47 cfm, and most likely more (no flow data for the Max Street Modified and Max Modified configurations).

My little bench isn’t calibrated, so the data contained in this post can’t be considered dead-nuts accurate, but its probably close, and the changes in flow resulting from the modifications most likely reflect the actual change in flow.

It looks to me like there’s plenty of juice to be had by playing around with your airbox, regardless of which filter you use.