what s a 30mm mikuni?

[zingshoen]

i d like to put this up for discussion:

http://www.pccmotor.com/30mm-mikuni-carburetor-crf-xr-200-30200250.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

+++

the 30mm mikuni is here:

http://www.mikuni-topham.de/ENGLISHSITE/ENGLISH/Frame_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)

[Weldangrind]

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.

[driller]

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

[zingshoen]

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?

[driller]

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.

[Weldangrind]

I agree.

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

[zingshoen]

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.

[Pliskin]

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.
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?

[zingshoen]

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.

[Pliskin]

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.

[zingshoen]

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 :-)

[Pliskin]

Thank you Zingshoen for the link.

[pete]

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

[xposur]

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.

Can you link me ot the TW 200 page?

[zingshoen]

xposur, sorry but...better late than never

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

they have a lot of info

[zingshoen]

http://www.mikuni-topham.de/ENGLISHSITE/ENGLISH/Frame_English.html

[Ariel Red Hunter]

I guess there is some confusion on Mikuni Carburetor sizes. The model number, like VM 26 refers to the diameter of the venturi. The VM 26 is also called a 30mm carburetor. That is because it measures 30 mm at where it bolts on to the engine. Carburetors have always been measured by the venturi size. All of these carbs are descended, in design, from the English Amal. It is easy to over carburate an engine. A 26 mm carb is close to a 1 1/16th inch Amal. Really fast 250's had 1 1/8th Amals, or about 27 mm venturi. So a 26 mm has proven very good on 229 cc singles. Unfortunatly, Mikuni does not offer a VM 27. I suspect that a VM 28 is just too big without extensive engine tuning, or hopping up. You will also loose low range sharpness by going to a VM 28, or, in other words, flexibility.

[Merlin]

I love seeing a thread go on for so long. Very good conversation. zingshoen did you end up using a vm28 and if so how did it work out?

[mtiberio]

I guess there is some confusion on Mikuni Carburetor sizes. The model number, like VM 26 refers to the diameter of the venturi. The VM 26 is also called a 30mm carburetor. That is because it measures 30 mm at where it bolts on to the engine. Carburetors have always been measured by the venturi size. All of these carbs are descended, in design, from the English Amal. It is easy to over carburate an engine. A 26 mm carb is close to a 1 1/16th inch Amal. Really fast 250's had 1 1/8th Amals, or about 27 mm venturi. So a 26 mm has proven very good on 229 cc singles. Unfortunatly, Mikuni does not offer a VM 27. I suspect that a VM 28 is just too big without extensive engine tuning, or hopping up. You will also loose low range sharpness by going to a VM 28, or, in other words, flexibility.

if you really want that 27, you could bore out a 26

[Ariel Red Hunter]

if you really want that 27, you could bore out a 26Yes, you could. But modifying venturi's is a very ticklish and precise job. A friend of mine did just that (on a Bridgeport lathe) modification on his Amal GP 1 1/2 inced venturi carb. That instrument was on his flat tracker Gold Star. It worked great at wide open throttle, wooley down low, but in flat track racing, down low didn't matter. You were always above 5000 RPM. It must have worked. That was one of the fastest Beezers at Gardena Raceway. Did well at the Sacremento Mile as well.

[2LZ]

Had one Amal. Man, I hated the carb. It leaked and drowned the bike on a regular basis. Very finicky. The Bing on my Husky was superior, even for a 'tickler".
I had not realized that the Japanese had copied the Amal. I can say they did a vastly better job if they stole the design.

[mtiberio]

I routinely run chinese knockoffs of Keihins modified to have an Amal mounting flange on my Guzzi with Amal compatible manifolds.

[mtiberio]

Yes, you could. But modifying venturi's is a very ticklish and precise job. A friend of mine did just that (on a Bridgeport lathe) modification on his Amal GP 1 1/2 inced venturi carb. That instrument was on his flat tracker Gold Star. It worked great at wide open throttle, wooley down low, but in flat track racing, down low didn't matter. You were always above 5000 RPM. It must have worked. That was one of the fastest Beezers at Gardena Raceway. Did well at the Sacremento Mile as well.

really depends on how wide the slide is relative to the venturi. Malossi used to bore the 40mm dell ortos out to 41.5 or there abouts...

[Ariel Red Hunter]

Had one Amal. Man, I hated the carb. It leaked and drowned the bike on a regular basis. Very finicky. The Bing on my Husky was superior, even for a 'tickler".
I had not realized that the Japanese had copied the Amal. I can say they did a vastly better job if they stole the design.Well, I had a different result. I could always get better carburation and better top end with an Amal compared to that tractor carburetor called the "Bing". But Bings did seem to work well on German and Austrian and Czech two strokers. I never got into tuning two strokes. I couldn't stand the noise. I never had an Amal that leaked. I also never had an Amal Concentric, of which I have never heard good things except in the magazine road tests.

[2LZ]

Well, I had a different result. I could always get better carburation and better top end with an Amal compared to that tractor carburetor called the "Bing". But Bings did seem to work well on German and Austrian and Czech two strokers. I never got into tuning two strokes. I couldn't stand the noise. I never had an Amal that leaked. I also never had an Amal Concentric, of which I have never heard good things except in the magazine road tests.

That explains it then. My history (younger years) is vastly two stroke over four stroke. Back then, a Yamaha 175 Enduro would kill a Honda SL and the Husky, Maico and Penton ruled the tracks. You race what you got..........

[pete]

That explains it then. My history (younger years) is vastly two stroke over four stroke. Back then, a Yamaha 175 Enduro would kill a Honda SL and the Husky, Maico and Penton ruled the tracks. You race what you got..........

then one day you are sitting on the start line on yer Montesa Cappa250
look left then right all yer could see was CR250M Elsinore's...

Honda had arrived....






..

[zingshoen]

I love seeing a thread go on for so long. Very good conversation. zingshoen did you end up using a vm28 and if so how did it work out?

i ve got the VM28 in my 200 cc Zong with a custom header and unrestricted muffler - and a quarter turn throttle. there is a bit of re-jetting to be done, i can post the details if someone's interested. I ve optimised the setup over the years and am very happy - bit like a two stroke, though! world of difference to the stock carbie.

[zingshoen]

I guess there is some confusion on Mikuni Carburetor sizes. The model number, like VM 26 refers to the diameter of the venturi. The VM 26 is also called a 30mm carburetor. That is because it measures 30 mm at where it bolts on to the engine. Carburetors have always been measured by the venturi size. All of these carbs are descended, in design, from the English Amal. It is easy to over carburate an engine. A 26 mm carb is close to a 1 1/16th inch Amal. Really fast 250's had 1 1/8th Amals, or about 27 mm venturi. So a 26 mm has proven very good on 229 cc singles. Unfortunatly, Mikuni does not offer a VM 27. I suspect that a VM 28 is just too big without extensive engine tuning, or hopping up. You will also loose low range sharpness by going to a VM 28, or, in other words, flexibility.

the guy at topham carbies gave me the specs for the VM28 which work on 180cc racing engines, so rather than engine tuning, one could try fine tuning the carbie - i think it works, but not everyone has been successful; using the VM26 should also work. a flat slide is where the difference kicks in.

[zingshoen]

Well, I had a different result. I could always get better carburation and better top end with an Amal compared to that tractor carburetor called the "Bing". But Bings did seem to work well on German and Austrian and Czech two strokers. I never got into tuning two strokes. I couldn't stand the noise. I never had an Amal that leaked. I also never had an Amal Concentric, of which I have never heard good things except in the magazine road tests.

ah...fondly remember Bings and Dell'ortos, fountains of joy for my younger days. remember to stick a rag under the BING coz it will leak :hehe:

[hertz9753]

I thought somebody said Taco Bell or maybe it was somebody talking about Bultaco and carbs. When I'm half asleep it means the same to me.

[Ariel Red Hunter]

I thought somebody said Taco Bell or maybe it was somebody talking about Bultaco and carbs. When I'm half asleep it means the same to me.You're half asleep a eight o'clock in the morning? What a life.

[Ariel Red Hunter]

the guy at topham carbies gave me the specs for the VM28 which work on 180cc racing engines, so rather than engine tuning, one could try fine tuning the carbie - i think it works, but not everyone has been successful; using the VM26 should also work. a flat slide is where the difference kicks in.The VM26 Mikuni does work on these engines, and works very well. You are the first guy I've ever heard of using a VM28 on one of these engines. So I'm all ears. As far as the flat side goes, What puts me off the OXO is that there is only one slide available. So, if it is too rich up to 1/4 throttle, you have to get a bigger carburetor, and if it is too lean you have to get a smaller one. That makes for very expensive carb tuning. Or maybe, I'm just too cheap.

[2LZ]

ah...fondly remember Bings and Dell'ortos, fountains of joy for my younger days. remember to stick a rag under the BING coz it will leak :hehe:

Indeed. Hold down the tickler until it floods. It has no choke. Once it's running, no more leak.
This one on my Husky still works great to this day.

[zingshoen]

Can you link me ot the TW 200 page?

I realised that it may not be clear that I am using the FLATSLIDE VM28-418 Mikuni in my ZongSierra200:

http://www.mikuni-topham.de/ENGLISHSITE/TM_Carburetors/VM28-418_English/VM28-418.html

[zingshoen]

Indeed. Hold down the tickler until it floods. It has no choke. Once it's running, no more leak.
This one on my Husky still works great to this day.

she s a beauty, yes she is :tup: