UFO??

[85RZwade]

Mark, for what carbs did you order the CSIs? I'm still wondering if I can get a pair to suit my VM30 2.5 brass slides right/left idle. The UFOs appear to be symmetrical and sold individually, the CSIs left idle only and sold in sets of 3. Also interested in your tuning results when you get that far!

[m in sc]

vm34s  with a 3.0 cutout

[1976RD400C]

I got a chance to tinker some more with the jetting after installing the UFOs with the store bought slides from Niche. This is the jet changes done. 34mm vm carbs.
   
Had 2.5 slides, new slides with UFO are cut to a 3.0 or maybe even 3.5   The UFO has 3.5 on the disc.   
Went from 50 pilot to 30.   Kept air screw at 1.75 turns out.   Wouldn't start or run without jet change.
Raised needle clip from position 2 to position 4 (richer).     Still too lean and pilot circuit lean.
Changed needle jet from P-2  to  P-4.   Kept clip on position 4. Turn air screw in to 1 turn out (richer).
Never did anything with the main jet (300)
Runs real good now. Pilot should go to 40 though.
I notice it really runs well from 0-1/2 throttle, real crisp and great throttle response. 0-1/4 throttle is sweet, real crisp, pulls hard.
Seems to run better now at low RPM 3500-4000 and putting it under load.
I never had a flat spot before but there is no sign of one now, at any RPM, throttle position, or load on the motor what so ever.
As for wide open, I'm not sure how the UFO does much because with the 3.0 slide the leading edge of the UFO is pulled way up in the slide chamber at WFO and just the very bit of the trailing edge is anywhere near the venturi area.
Another thing I noticed is the idle stop screw only needs to be turned 1/4 of a turn from touching the slide to get it to idle down low (maybe richer pilot jet will change that).
Also noticed my cylinder head temperature gauges read about 20 degrees higher now. When I opened it up temp went up to 350, it never went that high road riding before.
I'm happy, it seems to carburate perfect. I haven't had a chance to do a GPS log of a drag race to compare power. Going through the twisties and exiting turns the carbs are working perfect at any RPM. You do notice the crisp throttle response, and it makes easier to ride.  Normal riding when you are at 0-1/2 throttle is where you notice they are working nice and it improves the way it runs. I'm still going to tinker with the needle clip and install the 40 pilots.
               

[m in sc]

good info, very good. 

your head temp may be resolved with the pilot somewhat as well, curious to see. (the pilot does provide fuel through the whole range soemwhat)

[1976RD400C]

I got a chance to play with the jetting again. Installed a 40 pilot. Before UFO's I had a 50. After UFO's I tried a 30, way too lean at 1 3/4 turns on the air screw. Still too lean at 1 turn on screw. Now with the 40, it is too rich with air screw at 1 3/4 turns. Just a crack off idle it is popping away and it developed a slight richness going through 5500 rpm. The only thing I changed was the pilot and it developed the 5500 richness. I can tell the whole midrange is too rich now, just like Mark said a pilot will effect. The rich mid range slows down acceleration.  Also the temperature came way down, 30-40 degrees. So, a 35 pilot I think will put it spot on (unless I set air screw with the 40 at maybe 2 1/4 turns ?). Anyway, once the pilot and mid range is leaned some it should be right on the money. Looks like the jet changes for UFO's in 34mm vm carbs, on a stage II large reed motor will be:  50 to 35 on the pilot, 1 size larger needle jet, and 1-2 spot richer position on the needle clip. One odd thing is I can't get it to idle so low that it will stall by turning the idle stop screws way out. Maybe the UFO is not letting the slide to drop all the way down? Maybe it is hitting that shroud that sticks up on the needle jet? I better investigate that. (ya know, the cnc machined slide combo that cost $63 each  ) The bike was running stronger when it was leaner. The UFO's seemed to give it better throttle response. Once I lean the pilot circuit and maybe go from 2 clip positions richer to just 1 it will be just right. Final test coming soon (preview: it's not going to have 8 more hp, but will have a noticeable better throttle response).   

Things I'm learning:

      If you have a deserted rural area where you can play with the throttle position and speed you can really feel these carb jet changes happening and it isn't that hard to get it just right. The pilot circuit does effect the mid range. Too lean a pilot makes it run hotter.


Looking at the chart you see the cutaway change (2.5 to  3.0) leaned it at 25% throttle so the needle jet change corrected that (P2-P4)

[m in sc]

TIMELY AS I JUST GOT MINE.

so, what jet tube are you currently running? p4, or 2?

[1976RD400C]

P-4  and the needle is a 6F9

[racerclam]

I use UfOs often , I install many for my customers . They work great and cause a round slide carb to out flow a flat slide up to 13/16 throttle opening . I modify lots ofcarb with venturi dividers , both mods together are wonderful . They require a smaller pilot because the signal to the needle jet is increased and starts pulling much sooner causing a greater over lap during transition of circuits  also cuttint he slide arch is necessary usually 1 to 2 mm . The are worth the effort . Check out my web site richstaylordporting.com aor give me a call if you would like to know more

Rich

[racerclam]

More pics that wouldnt load

[racerclam]

again

[racerclam]

one more

[edgefinder]

The blades look like they could help but what tells you where or how many and how long does what?

[racerclam]

How many? Well I started with doing just 2 at half throttle position , the difference was evident ao I went to 2  Two at half throttle ann two at 1/4 . Worked even better noticable better snap and pull through those windows , Then about 10 years ago I tried 6  dividers 1/4 1/2 and 3/4 Waaaay better linear power through out . So I would say that experience told me what worked . How Long you ask they reach to the slide and conform to it with about 1mm clearence . I have alot of them out there . Go to my testimonial page of my web site and read what one guy said how it worked on his 2016 TM 125 with power valve . I told him thai I believed that with m carb a power valve wouldnt be necessaayso he did his own experiment , Check it out . I first did porting and carb as well as my reed conversion on His vintage racers on his 370 Bultaco as wel as hus Rickman Hodaka , both on the same page . I have don 15 carbs for a vintage snowmobile racer plus several port jobs and he won the biggest ice flat track race in the country with his Kohler 440 tripple that made 126 hp and 98 lbs torque . The is also a RD 400 on my site that had earned the #1 plate on east coast using my carbs and porting .

Rich

[1976RD400C]

I'm done jetting and here is what changes I did after installing the Niche slide and UFO assemblies on the VM34s.
 
                           Before                                                                       After

   Pilot                50   1 3/4 air screw turns                                      40    2 1/2 air screw turns           it's a touch ricer now, going to 35
Needle jet                 P2                                                                        P4
Needle clip            position 2 lean                                                      position 3 middle                     richer than before


0-1/4 throttle is super smooth, crisp and makes more power, acceleration is perfect with the 34s. 0-1/2 throttle same thing runs sweet. Full throttle may be making more power, not sure yet. It seems to pull up hills at low rpm better. It's running cooler with the pilot circuit a touch richer. One problem is I can't get it to idle under 2000rpm even with the idle stop screws backed out. All in all it makes the bike quite a bit easier to ride with the crisp smoothness, throttle response, and power that it is making by just using 1/2 throttle. I like.   8)

[m in sc]

I havent had time to play witht hem at all, but i did dig out the carbs and the inserts and mocked 1 up. this is what they look like. to me, way better built but cant speak to fuction.

I need to correct my drawing as the 'bolt' hole for the slide was a hair off (on me) and resubmit to bob for the 34's, but i can make these work.