Cheap HP mod? Mikuni VM flow optimizer

UFO installation and tuning, Part 3

I left off at the point of scraping the UFO plate to gain enough clearance to allow the slide to fully close. That is where I spent the next four hours. I went to the local drug store and purchased some children’s modeling clay (Crayola) and used it to locate the spots where the UFO plate touched the bottom of the carb profile. After trying various tools for scraping the high spots on the plastic (Utility and X-acto blades) I discovered the curved blade of my Buck knife (Model 110) was a nearly perfect choice. I will mention that the modeling clay is emulsified by gas and oil and I seemed to get it into everything on the carb during this phase. Someone mentioned to me that Wonder bread works for this sort of thing also, but it was too late. I purchased some carb cleaner to remove the gunk when I was done. My slide now fully closes.




Jetting challenges
The last reported PJ was one that had been soldered closed. It too proved to be too rich after full warm up. The next step in the installation guide is to drill an air bleed hole in the needle jet hood. So… because I was less than confident this would be race worthy on July 19, I went to Cycle Gear and ordered a new Q-8 NJ from Parts Unlimited in case I need to go back to the original jetting. I then used a #55 drill to place the air bleed hole as directed on my current Q-8 NJ. I was very close at this point but a little lean. I reinstalled the #15 PJ and it’s back to too rich. Drill out the air bleed in steps #52, #50, #47 testing each time with the #15 PJ. I am now about right and I have a functioning airscrew for air density adjustments at the track.




Performance testing on the street or just pissing off the neighborhood?
The claim is more low-end and mid-range performance, with .75 to 1.0 HP increases per 100cc of displacement. I can say with certainty that it sharpens throttle response. My feel is that the performance increase is throttle position sensitive in the low/mid RPM range. I can feel a difference in roll-ons and part throttle operation, but at full throttle it is about the same as before. This makes it better suited for off road use (IMHO) because Mxer’s tend to spend their time at one of the two extreme positions (On or Off) Still, may be of use on those sweepers.
A shared thought here on the limits of perception, I recently changed the porting on my 430 with the result of more felt low-end power and a big mid-range hit that was not there before. As a result, I cannot honestly say there is an improvement once I make it to the mid-range hit because if it is there, it gets lost in the crowd.
I hope to make it to the track on Sunday for some final testing and assessment.

Is it worth it?
I am going to say yes subject to further evaluation at the track. I am done or near so and there is a performance improvement. $30.00 does not seem like much to pay for ponies these days and I enjoy a personal project.
BUT… This is not a mod for the beginner. I spent at least 8 hours on this. I lost count of the times I removed, modified, installed and tested the carb. It is not “Plug and Play” by any estimate. I have a lot of experience and a machine shop at my disposal. Let the uninitiated beware.

Regards,
PC

UFO Installation final

I did at last make it to the track on Sunday. I had left the fuel tap on from the night before and when I got to the track the bike was very flooded. After a lot of cranking and pushing, it finally started and I was able to blow it out. I didn't think to do anything else but ride and began to make 5-6 lap sessions. After a few sessions I checked the plug (old) and it looked good but slightly lighter than before. I felt the bike was hard to hot start and tried a couple richer pilot jets. That was the ticket. With a #25 pilot the bike would start on the 1st or 2nd kick both hot and warm. I should note here that means I overshot the sizing on the air bleed hole. So if I had a "do over" I would stop at the #55 drill hole and head to the track for final setup.
As for perceived performance improvement on the track. It is difficult to tell. Big hits felt on the pavement vanish into wheel spin in the dirt and small improvements?...I think I can feel a bit more just as I open the throttle.
I'll say again, A lot of work and technical savvy required for installation and setup.

Regards,
PC