I observed the air/fuel ratio behavior during transient operation.  I would roll the throttle on and accelerate at a moderate pace, then shut the throttle and decelerate.  Note that on deceleration, the standard carb configuration had very mild afterfire, the typical cackle/crackle, but never any KABOOMS.  The UFO carb had absolutely zero afterfire, no cackle/crackle, no KABOOMS.

I don’t have a way to measure part throttle torque or power, but I felt that if part throttle torque is better, then fuel economy should also be improved.  I already had tested the fuel economy for the standard configuration when I did the carburetor shootout.  The VM38 got a best of 59.2 mpg.  So, I took the UFO configured carburetor on exactly the same fuel mileage test loop.  Due to the Covid19 shutdown, conditions were optimum for achieving good fuel economy.  There were almost no cars on the road.

The UFO carb used 1.66 gallons of 92 octane on the 79-mile test loop.  That works out to 47.6 mpg.

Conclusion:  Seat-o-da-pants the UFO carb and the standard carb are very close.  While the standard carb feels crisp the UFO carb feels torquey.  But that seat-o-da-pants stuff can fool you.  Hard data tells the real story.  IMO, the standard carburetor works much better without the UFO.  It mixes better.  It idles perfectly.  It makes more power.  It gets significantly better fuel mileage.  It’s way easier and cheaper to tune.  I really can’t see any advantage to the UFO other than zero afterfire.  I think I gave it a fair test.  I tried my best to get it to work as advertised.

I hope you find this report helpful.  Thanks to Lancer for letting me try out the UFO.

Knowledge is power.

Stay safe out there, respect the Vid19.  It’s serious stuff.

Mike

Very good information!
It`s interesting, your vm38 is different from mine, I bought it used recently, but im not sure if its an older version

Another well researched and well written piece. Thanks muchly!!

Maybe it's mind over matter. I'm sticking with the UFO. The bike feels like it has more power. My carb is a  vm 36mm.

Hey HotRod.  How did you set up your idle mixture?  Did you have issues with it being overly rich?  Lancer has posted that the UFO I had was a newer version.  It's supposedly a lot different than the older UFOs.  Do you know if your UFO is the newer version or the older version?  Do you have any pictures?  Do you happen to have any info regarding the difference between the newer version and the older version?

Eegore, you stated "I eventually tossed out all the additions and the Mikuni carbs."  Are you saying that you ditched the VM carb entirely?  What carb are you running now?

DragBikeMike ; I got my UFO about 9 months ago. Not sure if it's a old or new style. I had to sand the outer edge a little so it would drop into the slide. Still a tight fit, but flush. At first I could not control the idle because the UFO would not let the slide close to the bottom. A little more fine sanding fixed that. I ended up with a #15 pilot jet, a hole drilled in the needle jet hood, and the mixture screw about 1.4 turns out. I did try the blocked pilot but didn't like the lack of control in that section. Only by checking the spark plug do I see any sign of over rich at idle. No smoke from the exhaust. I'm running a KN cone filter at the end of the stock manifold hose and the DR cam.