UFO's

Adding UFO's to VM carbs is a way to improve throttle response, especially to piston ported engines. However, it will require time and effort to setup the carbs to obtain desirable results. Slides must be altered and rejetting will be required with slight differences to standard jetting procedures.

An installation manual from a popular UFO vendor is available here: http://www.3cyl.com/mraxl/manuals/ufo.htm
Note that both VM28SC and VM30SC slides have 28.3mm ID with 31.4mm OD.

Scott, (Looney Cylinders, LC), has spent a great deal of time tuning his H1 with UFO's and has offered his experience to be shared with those who may want to install UFO's. His notes follow (in no particular order):

*A guy MUST know what jetting parts/adjustments to target at each associated throttle positions BEFORE venturing into the UFO world. UFOs can provide excellent results, but only if set up properly. I'm betting any bad wrap UFOs have acquired over the years is due to the "tuning uneducated" suffering failures and giving up due to not following the above.

*Read and fully understand the basic carb tuning material at Dales's site.

http://kawtriple.com/mraxl/carbtuning.htm

In the Sudco Mikuni manual, there are graphs which illustrate which jetting parts control the areas of each throttle opening. The same graphs showing jetting parts and their associated areas of control are here:

http://www.mikuni.com/pdf/vmmanual.pdf

Proper tuning prior to UFO installation will make UFO tuning easier.

Installing UFOs is well worth it, but they do "re write" the Mikuni tuning rules/standards at the lower throttle openings...

Confirm your air induction system is clear (unis not over oiled or Emgo clones installed etc).

Get your iggy timing spot on and confirmed with a timing light @ 4000 rpms. Iggy timing plays a HUGE factor whether an engine behaves rich or lean.

Confirm the proper float lever level (VM34 is 22-24mm off base gasket surface with carb inverted). Again this setting plays a huge factor on whether a carb runs rich or lean per given jetting combo. Using the leaner 24mm setting often results in better setup.

You must mark your throttle housing and twist grip so determination of throttle position can be known where problem areas are occurring and the associated corrective action taken.

*Addition of UFOs into a VM really re-writes the tuning rules. One such thing is the pilot circuit. As such if an air screw is set to give the normal "highest idle" (provided the pilot jet is approximately the right size) the immediate off idle throttle response will be lethargic, possibly making the bike hard to launch at 1500/2000 rpms off the line in traffic. Get the setting right and one can ease the clutch out at 1500 while applying throttle at the same time with no bog or stumble (works well when the cops are nearby)

Turning in the AS by as little as 1/4 turn makes a huge difference in the off idle acceleration. Rich (to a point) really does make for a sharp accelerating engine upon the blip of the throttle.

On the road a UFO equipped carb will respond to as little as 1/8th turns AS (hence me carrying my famous screw driver). This is likely due to the tiny pilot jets (12.5-17.5 range rather than the typical 30-40 range) now in use.

*A few oddities with these UFOs. One thing is they lower the throttle range effected by the needle jet/jet needle all the way to full closure of the slide (rather than approximately 1/4 open). As such the airscrew setting/pilot jet determination must be done at a very slow idle with all three carbs on their stops (no dominant cylinder). Only in this configuration does the airscrew adjustment have any effect. If you try to set one carb higher in idle (to establish a dominant cylinder) fuel flow from the pilot jet circuit it is completely overwhelmed by flow from the needle jet.

*The UFOs alter the effective throttle opening range of the needle/needle jet circuit from the standard Mikuni slide installation. As such the normal NJ circuit range (which usually commences at about 1/8 throttle opening) has been lowered all the way down to slides on their idle stops. A page of the UFO installation manual clearly shows this altered range of NJ operation.

This is the second reason why VM carbs run so rich down low with the initial fitting of UFOs (the first reason being the cleaner airflow/pull on the pilot circuit).

Since the NJ circuit is now active with the slides on their idle stops, moving the needle one clip groove will result in about a 3/4 turn of the AS to correct the idle mixture (my observations with the current needle, but other needle profiles may be a bit different). This works both with raising or lowering the needle.

Usually the AS has enough authority to correct a 1 groove needle position change. However, if you move the needle by 2 grooves you now will most likely be into replacing the pilot jets, to get the AS back into an effective range.

This is why I stated to adjust the AS setting with all three slides synced and on their idle stops. If you try to raise only one slide to get a "leading" cylinder the NJ circuit on the leading carb will immediately be adding more fuel into the engine, hence giving a false AS setting.

Assuming your timing and float levels are correct, if you are trying to fix a rich issue in the first 1/4 to 1/2 throttle openings a smaller NJ is required (go to a P2). If you are trying to correct an issue in the 1/2-3/4 throttle opening a needle clip reposition is generally used.

Needle clip position will effect other areas than the above stated 1/2-3/4 and you can fudge things somewhat by doing this. This trait will become even more noticeable with the installation of UFOs, especially in the area when the slides are on their stops, or at very small openings. Trying to correct an improper area of throttle control with needle clip position will become deadly for your tuning effectiveness with UFOs installed.

If you are going to venture into the world of UFOs (and not get frustrated with poor results) you MUST be able to determine at what throttle opening an issue is occurring and be able to accurately target the offending metering device/adjustment to correct the issue.

*You might need #15 pilots (depending on how the fuel flow is between your needle/needle jet is at very small throttle openings)...

When using such small pilots the AS setting becomes extremely sensitive (1/4 turn can clean up 4 stroking at slow speeds/light loads)

Adjust your airscrews with the slides all synced on their idle stops (don't try to adjust with a "leading" cylinder, as the above mentioned needle/needle jet fuel circuit is now in effect at idle too).

*BTW, Since the needle/needle jet circuit is now in effect all the way down to idle (slides on their stops) changing the needle clip position can cause you to have to go to a different pilot.

*You will indeed find with UFOed carb 1/8 turn AS behaves like 1/4 turn in non UFO setup. If slightly lean you will feel a "pause" in throttle response coming off idle stops during riding. Lean will also make the bike hard to launch off the line without using allot of revs. Rich will show up as 4 stroking here, especially under light load.

Make yourself a 2 foot long screw driver out of a piece of welding rod for quick roadside AS adjustments if needed. Adjust AS 1/8 turn each time and re try as req'd.

Take note: Any needle movement (clip re-position) will effect the idle mixture, as needle/needle jet circuit is now active starting at and including idle. As such you will need to vary AS setting and/or pilot size.

For correction of rich/lean mixtures at a specific throttle opening:
Needle clip position tends to effect the 1/2-3/4 throttle positions the most, whereas needle jet size mostly effects 1/4-1/2 throttle openings. However clip position will have some effect on lower throttle openings too (shows up big at idle). Conversely NJ size seems not to effect the more open (1/2-3/4) throttle positions.

I've set my bike (500 with 3.5 CA UFOs/ VM34s) to run just rich enough to drown ping (91 oct pump gas), while on the pipes (7000+). As such it tends to be somewhat rich in an off the pipe scenario (but no 4 stroking).

Your main jet selection will be unique to your bike and will have to be determined by plug chop at WOT due to your use of super high octane gas.