Mikuni Carb Settings

[Duccout]

Here are my Mikuni settings as delivered by Motocarb:

VM28-49

Main jet 140
Pilot jet 25
Needle jet 169 0-2
Needle 5F21
Slide 2.0
Main air jet 0.5

I have yet to tune it in and the next step is a 27.5 pilot jet. I'm hoping that the slide is correct as the cutaway is smaller than others are using.

I don't know if anyone makes a manifold with 52mm stud centres, which would be a lot easier to fit than a 50mm one which is made for British bikes.

[Bob_Matthews]

I believe jesus sells one, but not sure if it's suitable for a Mikuni. [Adaptador carburador fijacion por abrazadera (Dellorto, Bing, Keihin, ..) NUEVO especifico motores Ducati monocilindrico. Ddiametro exterior Ø ext. 35mm (orientacion ladeada).]

http://recambiousado.com/venta/index.php?id_product=5639&controller=product

[Duccout]

Thanks Bob, that could be used with a rubber hose connector.

[Dan C]

For the information of members the current settings on my VM 30 Mikuni Carbs:

350 Desmo 1968
Pilot jet 30 (VM 22/210)
Main Jet 160
Needle Jet P5 (159 Series)
Needle 6F5 (middle notch)
Air Jet - Removed
slide 2.5 (VM34/110)
Needle Valve 3.3 (VM 34/39)
With these settings there is still a bit of surging at low rpm and plug colour is indicating rich at those rpm, I'll adjust the needle position first - if that doesnt cure it then try a 25 pilot

450 Desmo 1974
Pilot jet 35 (VM 22/210)
Main Jet 180
Needle Jet P5 (159 Series)
Needle 6F5 (bottom notch)
Air Jet - 2.0
slide 2.5 (VM34/110)
Needle Valve 3.3 (VM 34/39)
With these settings it starts easily, idles reliably at 800-1000rpm and runs cleanly through the rev range.

Obviously a VM 30 carb is not what you'd get if performance was what you were after. But for general all round rideability it suits me well.

Cheers
dan

[Duccout]

I am a bit baffled by all the different needles, there seems to be an infinite variety and how do you choose the right one?

[ranton_rambler]

I don’t know anything about Mikuni carbs, but needle details for Dellorto are easily found on line. I drew them out at a large scale so I could see which were leaner and which were richer at part-throttle.

[Eldert]

Hi Guys

all the best in the New Year .

Mikuni needle charts could be found in the book Performance Tuning in Theory & Practice ( four strokes )
by A . Graham Bell

Eldert

[Duccout]

Thanks Eldert. I've been fiddling with Dell'Orto and Amal carbs for 50 years, but their needles are few in number and have a simple part number, e.g. K3, K4, K5, but Mikuni seem complicated by comparison, but I guess even my old brain will get used to it.

[ducwiz]

Hi Guys

all the best in the New Year .

Mikuni needle charts could be found in the book Performance Tuning in Theory & Practice ( four strokes )
by A . Graham Bell

Eldert

Dear all,

first of all i'd like to wish you a happy new year, and many trouble-free miles or kilometers in good health !
The book Eldert quoted is available as a scanned pdf. I have extracted the pages dealing with the Mikuni carbs, please download here: https://www.sendspace.com/file/zhsl0d.
Those who are interested in the entire book can send me their email adress, and i will return a download link in turn.

Best regards Hans

[Duccout]

I have changed my pilot jet for a 27.5, hoping that it would help, but I still cannot get the engine running properly, every so often it backfires through the carb and cuts out. The pilot air adjuster does not appear to make any difference, and it is a real pain to try to get a screwdriver on it as the frame and tank are in the way.

Any suggestions? I would suggest that the slide cutaway is too large, but as it is a 2.0, which is quite small anyway, I think that a 1.5 would be too small.