Clive,
It is remarkable what a little streamlining will do for a carb bore. The 36mm Mikuni VM roundslide I have on the bike comes stock with a #35 pilot jet, which I promptly changed out for a #30 to get the low range proper. It was set at about 2-2.5 turns out, so I could have gone down one more size tot he 27.5, but did not have that jet at the time so I just left the #30.
The instructions say to cut the pilot # in half, so a # 15 would be the desired jet, but I did not have one on hand ... a #20 was the smallest in my box so I went with that one initially (3 turns out). It ran but was very rich with a fair amount of black smoke out the pipe. My next order to Sudco included about 30 assorted jets, pilot and main jets, so I would be ready for the marathon tuning sessions. I was still not quite convinced that I needed to go all the way to a #15 yet, so I dropped it to a #17.5 ... 3 turns out & still RICH. So I finally put in the #15 pilot ... 2.5 turns out ... the engine liked it better but it was still a little rich. The instructions say that if you get down to the jet that is half of the original and it is still running rich, then to avoid getting too lean on the mid and high range, instead of dropping another pilot jet size you can drill a tiny hole in the cupped portion of the needle jet that sticks up in the carb bore. That will lean the low range further without affecting the mid-high range more. So I drilled the hole(the actual size was between the 1st and 2nd size recommended), and it helped noticeably. I am set at 2 1/4 turns out right now with a slight rich low range. I am going to drill out to the next size hole, and I think that will do it for the slow speed range.
I have set the needle clip on the 4th slot and am running a #240 main jet to make up for the smaller pilot jet.
The responsiveness is amazing, in fact it is almost too sensitive. When cruizing down the road in anything less than half throttle it is sensitive to the point of being almost squirrally. If I even think of moving my hand it responds. I have to actually concentrate on keeping my throttle hand motionless. It reminds me of when I first started learning to fly helicopters. The control touch sensitivity is so fine that you have to train your reflexes to respond in an automatic, unthinking fashion, so as not to OVERCONTROL. The throttle touch is that fine now. Hitting the throttle at any speed, but especially at slow speed, gets immediate response. The midrange is very strong and the high range is much stronger as well. I will be going up to a #250 main jet when I pull the carb for the needle jet drilling.
Before the UFO install the #250 jet had been a little too rich, with soggy performance in the high range, but I expect it will be the final main jet now with the other changes that have been made.
I have been very impressed with what a little $30 piece of quality plastic will do. When you think about it, going from a #30 pilot to a #15 and also include the drilling in the needle jet, it is amazing. That is dropping
SIX PILOT JET SIZES & THAT IS A BIG CHANGE IN ANYONES BOOK.For a carb that lists for $140, plus a $30 add on, $170 get you a lot of performance.
The bench flow testing done with a VM roundslide + UFO vs a TM flatslide showed what this thing can do. The testing included about 10 positions from idle to full throttle, and the VM + UFO outflowed the TM flatslide in 3/4 of the positions. If I remember right, the TM had a very slight edge in about 3 positions, the VM a slight edge in about 3 positions, and the VM well ahead in the other 4 positions. Something like that.
Gotta go, domestic responsibilities call.
klx650sm2002 wrote on 12/31/69 at 16:00:07:Hey Lancer
It seams like you are getting FCR type performance with this UFO at a fraction of the cost.
Clive W
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