UFO main jetting for vm30s

[waktaylor]

Regarding UFOs in VM30s.

I know the pilot jet needs be reduced by at least 50%.

Question here is what did you need to do for the main jet and needle clip?

[m in sc]

it's not always 50%. try going up on the pilot a bit 1st

[DesmoDrew]

   What I found regarding the idle (I have had UFOs in the race bike for years  ), is that without the UFO installed, the slide can mate to a recess in the floor of the carb bore and is able to fully close (with the idle screws totally out).  But the UFO (installed in the slide) actually contacts the bottom of the bore of the carb slightly before the slide bottoms out.  It can prevent you from getting a lower idle since the slight interference keeps the slide slightly raised and can actually keep the idle screw from even coming into contact with the idle slot in the slide.  So, look into the bore of the carb and see if you can spot where the UFO contacts the bottom of the carb bore and do a tiny bit of trimming.  Then you should be fine.
   

[waktaylor]

Hey, thanks. What do you typically do for the main?

   What I found regarding the idle...

[Hawaii-Mike]

My H2-motored H1 has the stock VM30 carbs and Ivan's jet kit.  I can share with you what changes were made due to UFO's and chambers.

Stock pilot is 35.  With UFO's it's running a 17.5.

Slides were not changed (2.5 cutaway).

Needle - center clip (same as stock).

Main jet - original size is 105.  With my setup the mains are 112.5.  This maybe a tad rich.  I don't run the bike at high rpm's for a long time because I'd get a speeding ticket for sure.

Regarding your question about the main jet, I don't recall having changed the size due to UFO installation.  The UFO's mainly help with mid-throttle acceleration.

[m in sc]

   What I found regarding the idle (I have had UFOs in the race bike for years  ), is that without the UFO installed, the slide can mate to a recess in the floor of the carb bore and is able to fully close (with the idle screws totally out).  But the UFO (installed in the slide) actually contacts the bottom of the bore of the carb slightly before the slide bottoms out.  It can prevent you from getting a lower idle since the slight interference keeps the slide slightly raised and can actually keep the idle screw from even coming into contact with the idle slot in the slide.  So, look into the bore of the carb and see if you can spot where the UFO contacts the bottom of the carb bore and do a tiny bit of trimming.  Then you should be fine.

nice.
i need to get mine out of the bag and play with them, makes sense. 

[waktaylor]

Before ufos I was running decent on Chucks base line p2 needle and needle jet, 47.5 pilot, 280 main.

After ufos not so much.

I stepped from 30 to 17.5 on the pilot. Ended up with air screw closed and the needle all the way lean to get the idle down and still not running properly. Starts easy (vape cdi thanks) but Won't rev under load.

I changed to 300 and 320 mains which seem to have made it worse.

I'm wondering if I need to drop to a 270 or less main?

Done for now. Beer:30.

[1976RD400C]

My UFOs with modified slides seem to work out real well on 34mm carbs. Pilot went from 50 to 35. Needle circuit was way lean after UFO install. Went from P2 to P4 and moved clip 1 groove richer. Left the main at 300. Idle stop screws just barely touch the slides for a low idle.

[racerclam]

I install alot of UFOS and on every one regardless of carb size  i cut the slide 1 to 2 mm depending on application and most work well wit a 20 pilot , It does not affect main jet . I actually massage the eyebrows on the bottom for better throttle closure . I also grind a trough in front of the needl jet opening that helps clean up the bottom end a bit as well as cut the needle jet shroud down from 8mm to 4mm . I do that even without a UFO. The new UFOs for the 36 and 38 mm carbs fit better now as I redigned them for Thunder products and over saw the build of them right here where I live. And another good thing is that you dont have to do any grinding inside it to get the cable to be installed .

Rich

[waktaylor]

Rich, could I send you my slides for mods? Will the p2 jets work still?

I install alot of UFOS and on every one regardless of carb size  i cut the slide 1 to 2 mm depending on application and most work well wit a 20 pilot , It does not affect main jet . I actually massage the eyebrows on the bottom for better throttle closure . I also grind a trough in front of the needl jet opening that helps clean up the bottom end a bit as well as cut the needle jet shroud down from 8mm to 4mm . I do that even without a UFO. The new UFOs for the 36 and 38 mm carbs fit better now as I redigned them for Thunder products and over saw the build of them right here where I live. And another good thing is that you dont have to do any grinding inside it to get the cable to be installed .

Rich

[waktaylor]

Thank you for this input. I was thinking the needle may be too lean now.

My UFOs with modified slides seem to work out real well on 34mm carbs. Pilot went from 50 to 35. Needle circuit was way lean after UFO install. Went from P2 to P4 and moved clip 1 groove richer. Left the main at 300. Idle stop screws just barely touch the slides for a low idle.

[waktaylor]

I think my bike was seriously lean before I installed the ufo. After reducing the pilot for the ufo the carbs have no where near enough fuel flowing.

How do you drop 27.5 through the pilot and not have to increase your main unless your main was already rich?

The mikuni vm manual indicates the pilot adds fuel through the entire range. Is that wrong?

[1976RD400C]

If after you install UFOs, your bike won't start easy and you can't pull from a stop, you have to richen the needle and or the needle jet by quite a bit, like 3 steps on the needle clip or a bigger needle jet tube. Once you got that going then while you are riding it see how the pilot circuit is doing. If while coasting it is bucking then too lean. If when you just crack the throttle open it is rat tat tatting, too rich. Try adjusting the air screw to correct that and if not change the pilot jet. Then you can work on the main jet but you need to go full throttle. Look at the hole in a pilot jet compared to a main jet. The difference in the amount of total fuel being used at full throttle between a 27.7 pilot compared to a  30 pilot is  miniscule.

[m in sc]

I think my bike was seriously lean before I installed the ufo. After reducing the pilot for the ufo the carbs have no where near enough fuel flowing.

How do you drop 27.5 through the pilot and not have to increase your main unless your main was already rich?

The mikuni vm manual indicates the pilot adds fuel through the entire range. Is that wrong?

the pilot is always on, yes, but the percentage of fuel it supplies as the slide opens becomes proportionately much less . if the change in pilot requires a main jet change, your main was right on the edge or wrong to begin with.   

[waktaylor]

This is good info too. I went from 47.5 to 20 on the pilot. Thays what I meant by dropping 27.5 out of the total fuel circuit.

It starts very easy but it also rat at tats and won't pull away from stop sign unless I work the throtttle to get it revving.

If after you install UFOs, your bike won't start easy and you can't pull from a stop, you have to richen the needle and or the needle jet by quite a bit, like 3 steps on the needle clip or a bigger needle jet tube. Once you got that going then while you are riding it see how the pilot circuit is doing. If while coasting it is bucking then too lean. If when you just crack the throttle open it is rat tat tatting, too rich. Try adjusting the air screw to correct that and if not change the pilot jet. Then you can work on the main jet but you need to go full throttle. Look at the hole in a pilot jet compared to a main jet. The difference in the amount of total fuel being used at full throttle between a 27.7 pilot compared to a  30 pilot is  miniscule.