Mikuni Carb Settings

[Dan C]

Can anyone offer guidance/suggestions on Mikuni VM30 Carb Jetting for the following bikes. All bikes have stock heads.

Widecase 350 Desmo
Widecase 250 Desmo
Widecase 250 Mk3

All bikes currently have worn VHB 29's and after rooting around with the VHB on the 450 I'm not going down that rabbit hole again. Most likely going to buy new Mikunis so any other random suggestions regarding fitting etc would be welcome.

Cheers
Dan

[Jordan]

There's discussion here:
search.php?keywords=Mikuni+jetting

Maybe contact Sudco in USA, to see if they can advise?

If you are going to chuck out the old VHBs, I'll take 'em.

[Dan C]

Hi Jordan,

Thanks for that. Should have mentioned I had done that search and got the info on the VM26 fitted to a narrowcase. The rest were much bigger carbs for race bikes. I'm just hoping to get a starting point for everyday type riding. Easy starting, good idle, and good midrange. At my age performance is nice but not necessary!
Sorry I wont be chucking the VHB's out. They'll be carefully stored!

Cheers
Dan

[graeme]

What’s happened to Nick “put a mikuni on it” ???

[Dan C]

Just an update on what I've found so far on widecase 350 desmo with VM30 Mikuni

Pilot jet. Started with a 40 which is too rich. Went down to 35 and still too rich. Installed a 30 but haven't tested that yet.
Needle 6F5 and Needle jet P5 (159 series). This is the combination that it shipped with from Mikunioz and seems to be spot on for the midrange. See photo of plug chop.
Main jet 250 as shipped. I haven't done a WOT test for the main so don't know about that yet.
Hope this might help anyone else thinking about a Mikuni. I'm very pleased with it.

[Duccout]

Did they supply a manifold to fit it?

[Jordan]

Thanks Dan.
I always keep info like this, in case I need it later.
Let's know what your final settings are, when done.

[Dan C]

Did they supply a manifold to fit it?

A very good question. They offer a variety of manifolds. I chose a straight manifold, which comes with the rubber boot and gasket. See pic.
Mounting the aircleaner was the main problem. The OD of the inlet flange is 58mm and aircleaners that big wont fit under the tank. I got a rubber boot of the correct diameter (from the plumbing dept of Bunnings.....) and mounted an aircleaner with a smaller flange inside the boot. Still had to raise the rear of the tank about 15mm.
With the benefit of hindsight a better and cheaper solution would have been to purchase one of their reducing rubber boots. This reduces from 40mm on the carb to 35mm on the stock manifold. Because the stock manifold has a slight bend the carb will sit lower giving more room to mount the air filter.

[Dan C]

Let's know what your final settings are, when done.

Will do Jordan. But just letting you know it will be a while. I have the head off to adjust valve clearances and tidy up various other things and have yet to order some parts etc.

Cheers
Dan

[linker48x]

So, a suggestion, borne of experience. Find a bike with a similar displacement and state of tune, probably a two valve Japanese enduro bike, and use that as a guide. Sudco probably sells a prejetted 30 mm carb for one or more of them. A 250 or 350 four stroke enduro bike with, say, a 30 mm carb will be much closer in horsepower and rpm to your street bike, than a roadrace bike with a 38 mm carb on it.

The frustrating thing about Mikunis is, their jets are very close together in effect. That allows very fine tuning changes, but you have to make fairly big changes to get in the ball park to start with. This is a way to get closer to what you need, and save some time.