what s a 30mm mikuni?
 

i d like to put this up for discussion:

http://www.pccmotor.com/30mm-mikuni-...-30200250.html

seems to be a 26mm mikuni as stamped on the carbie in the 5th picture. Carburetors are measured by bore size not by inlet or air intake openings.

or could i be wrong here? :? :D

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the 30mm mikuni is here:

http://www.mikuni-topham.de/ENGLISHS...e_English.html

click on VM carburettors
scroll to VM30-83 that s the mikuni roundslide carbie
40mm front and 58 mm rear spigot diameter

flatslide would be better, but at least its 30 mm are real :-)
+++
the 26 mm carbie may have its applications, but for a 250 cc it would be underpowering.

or could i be wrong? 8)

The carb you first pointed to is what I affectionately refer to as a 30mm Mikuni, right or wrong. What I know is that they work well in a 200-230cc application with the right jets. I've installed them several times, and my best experience with a 200 has been a 110 main and a 25 slow jet. I'm still tweaking the 230, but it seems to like a 30 slow jet and a 115 main.

The castings are excellent, and jets are very easy to find. Throttle response is much improved over the Keihin clones, IME.

I truly think what we all use is a vm22 but I could be wrong, look at the jetsrus.com site

ok, that makes more sense. it fits with the jets used by weldandgrind. the jetsrus gives 100 / 30 as standard jet sizes for that carb, while the 26mm takes a 190 main jet and a size 60 pilot.

so it s a 22mm, not a 30 mm carb after all, it seems so far 8O that s not so big, the 50 cc kreidler motors worked with a 21mm dellorto 8)

anybody having good results with a bigger carb on the 230cc OHC motors?

The intake measurement on these carbs are 30mm but the inner throat may be in the 22-26 range depending on make and model. It seems Mikuni and Keinin both measure this way but most people use the intake size when discussing carbs.

I don't know what would be gained by going larger as this size seems optimized for this size engine and a larger carb would make dialing it in a real bear. Imagine putting a pair of 4 barrel carbs on a 4 cyl toyota corolla.

I agree.

Whatever the actual measurement of the so-called 30mm Mikuni is, it's perfect for 200-230cc air cooled four strokes.

in my experience somewhat larger carbies can be very good, i mean very good :-) unless you overdo it. that aside, space limitations are an important concern, as with cars, where your big hollley wont fit under your corolla's bonnet to begin with :-)

but 4 mm more are not excessive, with the other mods on the periphery done. the 28mm (genuine) slide mikuni i have on the zong (as a result of perusing the TW mod site http://www.tw-parts.com/ ) makes a world of a difference.

i recently bought a new zongshen 230 OHC engine (580 A $) and aforementioned 22mm Mikuni (80 A$ = importers don t necessarily pass savings onto consumers), so i ll see how that goes. i think i ll try to compare it to a 28 mm or 30 mm slide Mikuni eventually, provided it all fits into the XL frame. the logic of it is that the 200 cc Zong does well with the 28mm, so the 230 cc could probably do with a couple of extra mm.

Zingshoen, where did you get this carb and did you gain more speed with this mod. Wouldn't changing jets on stock carb achieve the same result?

i rejetted the stock carbie but found it very limited. once I got the jets for the 28 VM mikuni slide carbie right (i use a 260, whatever that means, with a unifilter), the zong runs like a different bike. before it ran more like a scooter. i m sure she s faster but i haven t measured it. say 85 in third gear, revving high?

if you have questions, let me know, but i ll be offline for 10 days or so, will reply then. i got it from a guy in adelaide, forgotten his name but if you google mikuni australia you get him, he s in a or south australia.

btw: the 28mm VM Mikuni is listed on the modifications list of the TW 200 page, for all modded engines and setups up to 230 cc. i think it s the way to go, but sure there are other ways, with different results.

Thank you so much Zingshoen for clarifying it. :) I will keep this in mind if I need to do this type of mod down the road.

no worries. have a look here:

http://www.iwt.com.au/mikparts1.htm

isn t cheap though. those prices are from the time the aussie was low. you d get a better price ordering from europe where the vm28 is around 150 Euro.

also i do use a 280 jet, not a 260, the 260 still was a tiny bit lean on full throttle. acceleration is the main effect, and i measure that in front shock rebound in 2nd 3r and 4th gear :-)

a 200 is cool. but it may as well be one that rocks...and modding is half the fun :-)

Thank you Zingshoen for the link.

These OKO flat slide carbs get a pretty good rap
with the twin shock trials guys....
I have ordered a pre jetted one for my Cota 348

http://www.mid-atlantictrials.com/Sales.html

Can you link me ot the TW 200 page?

xposur, sorry but...better late than never

http://www.tw-parts.com/

they have a lot of info