How to read the Mikuni jet needle chart

[tirebiter]

With help from Chuck78 I was able to download a Mikuni needle chart. It's not written in English but the numbers are


http://www.docstoc.com/docs/147891695/Mikuni_Nadelnxls---mintelonline

or go to docstoc.com, copy and paste the rest of the URL into your browser address bar :

/docs/147891695/Mikuni_Nadelnxls---mintelonline


I'm attempting to figure out how to read it and by doing so, select a jet needle for my "Little Suzy" that will hopefully deliver better fuel economy and still retain good power and maybe even improve on the othewise perfectly acceptable, driveability.


I'm beginning to understand that Mikuni needles have one, two or three tapers each. The one taper needles have a straight or linear profile from the thickest part up near the e-clip grooves, down to the thinnest, furthest from the grooves. The angle of the taper is consistent from somewhere just below the grooves, all the way to the narrow tip.

The two taper needles have one distinct angle change in the profile. The three tapers have two.

Apparently the chart does not show all the diameters between the thick and the thin parts of a sngle taper. It shows only the end diameters of the tapered portion.

The chart also seems to give a distance from the top end of teh needle, down to where the taper begins. It also shows a dimension which is apparently how far the top of the middle e-clip groove is from the top of the needle.

If anyone wants to fill in some more details and suggestions on how to make sense of the chart, please do so.

 

[trevor]

Link says "page does not exist"....

 

[tirebiter]

Link says "page does not exist"....

Trevor, Sorry about that.

I tried to fix the link in my previous first post and also added the complete URL ... in two pieces

go to docstoc.com, copy and paste the rest of the URL into your browser address bar :

/docs/147891695/Mikuni_Nadelnxls---mintelonline

 

[tirebiter]

OK, so it turns out the Mikuni needle chart is an interactive file. When opened you can see two charts. At the top of the page is a box where you can type in some details. Specifically mainjet, needle jet, needle type and e-clip position/groove.

The carts change accordingly to show the cross-sectional area nozzle - "D?senquerschnittsfl?che" and the needle profile - "Nadelkontur".

Now I need to collect up the designations for as many stock needle types that are still avalable and start plugging them in. This Mikuni Needles "Nedeln" chart works VERY WELL !!! So does the Google translate web page.

 

[Chuck78]

OK, so it turns out the Mikuni needle chart is an interactive file. When opened you can see two charts. At the top of the page is a box where you can type in some details. Specifically mainjet, needle jet, needle type and e-clip position/groove.

The charts change accordingly to show the cross-sectional area nozzle - "D?senquerschnittsfl?che" and the needle profile - "Nadelkontur".

Now I need to collect up the designations for as many stock needle types that are still avalable and start plugging them in. This Mikuni Needles "Nedeln" chart works VERY WELL !!! So does the Google translate web page.

That URL above is no longer valid, here is a more revised version of that file.

http://www.mintelonline.de/Dokumente/Technik/Vergaser/Mikuni_Nadeln.xls

mintelonline.de/Dokumente/Technik/Vergaser/Mikuni_Nadeln.xls


Click on the tabs at the bottom to view the fairly comprehensive listing of Mikuni needles. About the 1,000th line down in the document are the 5DL35 / 5DL36 etc needles that come in some of the GS high performance carbs.

I will save this to my computer due to how helpful and extensive that list is, in case this URL becomes invalid in the future.


Also I should note that the aftermarket Keyster or whatever Y-64 needles that look like the 5DL35/5DL36 are in fact substantially richer despite almost looking the same to the naked eye.
I think that running them in the 2nd lowest (2nd notch from the top) would be a good intermediate position, and bike's requiring a lot more fueling may need them in the middle position. The taper starts about 2 clip positions sooner, and down the the middle of the taper is nearly 3 clip positions sooner in the throttle range. The base diameter is also slightly skinnier, and say for instance a GS550/750 running an 0-6 needle jet would need the equivalent of an 0-4 or O-2 GS1000/GS850 needle jet (or Kawasaki O-3) to get the same fueling as the 5DL35/36 Mikuni needles. I compared the two in my measuring calipers to determine this. If you are top lean at 1/8 to 1/4 throttle, this will DEFINITELY help! The rest can be adjusted via the clip position.

 

[Chuck78]

0-2 = 2.610 mm
0-4 = 2.620 mm
O-6 = 2.630 mm.
P-1 = 2.655 mm (0.001" larger than an 0-6 jet)

These fine increments allow exact tuning for just off idle and early transition when mated to the correct length/shape needle. They do affect the whole rev range, but are definitely more pronounced at the lower end.

Enjoy the journey!

Here is some pertinent information above from another thread from Ian in New Zealand.
As you can see, the needle jet sizes o-2, o-4, & o-6 are only separated by .0004" / .05mm diameter. This sounds very miniscule, but from my experiences, going between o-6 to o-2 on a big bore GS750 produced very noticeably different running characteristics, which were also supported by giving me substanally leaner readings on my wideband o2 UEGO sensor / AFR gauge setup. Going big bore was sucking a lpr more air and fuel through, & I was a fair bit richer off idle. I tried going to o-2, & it was too lean. I bought some Suzuki OEM o-4 needle jets, but despite coming in a Suzuki package with OEM part # label, they were in fact 250 series o-3 needle jets for VM carbs (used on some Kawasaki KZ1000 etc VM22 carbs. These were acceptable but still a touch lean, and I went back to the o-6 with a lot more scrutiny over the float height level and pilot fuel screw settings, and got it sorted out fairly well. Fuel economy was ever so slightly lesser when cruising primarily on the pilot/needle base diameter, but it ran VERY well (smooth & STRONG!), and o-4 are very difficult to find, as are GS850 VM26SS carbs, '79-only!