The slide diaphragm is fragile.  Handle with care.  Gently work it out of the groove in the top of the carburetor, and then pull the slide up and out.  Note the orientation tab in the lower right corner of the picture.  Those two small screws you see can be difficult to remove.  They lock the slide needle in place.  Don’t attempt to remove the screws until the slide & diaphragm have been pulled out of the carburetor.

To adjust the slide needle, you have to remove those two small screws that I mentioned previously.  I find that an impact driver with an extra-long bit is the best tool for the job.  It’s very easy to round out the head of the screws.  The impact driver helps to prevent that.

It’s best to use an assistant to hold onto the slide while you lightly tap the impact driver.  You need like four hands to wrestle with the thing.

Raise the needle about .05” by replacing the .110” thick white nylon washer with a .06” thick washer (.27” OD x .12” ID).  You can find all sorts of suitable washers at the hardware store.  Just make sure that the ID fits over the needle and the OD isn’t larger than the original white nylon washer.  It must fit into the socket in the bottom of the slide.  This shows the original .110” thick washer replaced with a .06” thick washer.

Install the assembly with the slide on its side so that the spring and lower washer don’t fall off.

Like this.

There’s a groove in the top of the carburetor that accepts the raised lip on the periphery of the diaphragm.  When you install the slide assembly, you must make sure that the lip on the diaphragm fits nicely into the groove all the way around.  You also must pay attention to the orientation tab on the diaphragm.  It goes in the notch (circled in red).

Reinstall the slide spring and the carburetor cover.  Be careful not to pinch the diaphragm.  Then reinstall the fuel tank and seat.  Ready to rock & roll.

The motorcycle runs so much better.  You won’t believe it’s the same bike.  It has loads more power.  The obnoxious afterfire is almost completely eliminated.  No more KaBoooms.  It idles good.  The lean surge and hiccups at part throttle are gone.   It runs freely past 6500rpm in 1st through 4th gear.

I did a noise test with the NIOSH app.  Noise level at 1300/3000/4000 rpm is still 57/74/77 dB.  I was surprised.  I thought it would increase more than 1 or 2 dB.

Acceleration tests were impressive.

Second Gear 4K to 7K: 4.32 seconds            Improvement: 0.28 seconds

Third Gear 4K to 6.5K: 8.04 seconds            Improvement: 2.44 seconds

Fifth Gear 3.5K to 5K: 7.78 seconds            Improvement: 1.69 seconds

Fifth Gear 3.5K to 5.5K: 13.62 seconds      Improvement: 8.81 seconds      

Now, it will pull all the way to 5700 rpm in fifth gear, where before it would not pull past 5500 rpm.  On the freeway, it has reserve passing power.  You can merge onto the freeway without fear of being run over.

Fuel mileage was good.  I averaged 55 mpg over several tanks of gas.  Fuel economy dropped 2 mpg.  That’s fine with me.  The dramatic improvement in performance is well worth 2 mpg.  Chalk one up for the #55 pilot jet.

It seems to run a bit cooler.  On the freeway at steady state, it hangs in at about 310F.  Highest I observed was 319F.  I attribute the reduced temperature to the rich part throttle mixture.