what s a 30mm mikuni?

[zingshoen]

http://www.mikuni-topham.de/ENGLISHS...e_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]

Originally Posted by 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.

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

[Ariel Red Hunter]

Originally Posted by mtiberio

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

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.

[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]

Originally Posted by Ariel Red Hunter

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]

Originally Posted by 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.

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]

Originally Posted by Ariel Red Hunter

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]

Originally Posted by 2LZ

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]

Originally Posted by 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?

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]

Originally Posted by 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.

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]

Originally Posted by Ariel Red Hunter

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

[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.