Mikuni Kogyo Carb

Classic Norton Commando Motorcycles.

Mikuni Kogyo Carb

Postby brianchahn » Wed Jul 29, 2009 4:08 pm

Question about the Carburetor that came with my 72 Norton (came in a box of parts). The only markings on it are MIKUNI KOGYO JAPAN, and MIC on the other side.
Will this be a sufficient carb for the bike?

I also have the two to one machined part, but don't know the correct size screws in the picture below. They do not seem to be the same size as the ones the other ones for that part that screw into the block. I think it might be a 7mm or something.

(second to last pic is not mine.. i got it off the net)

Does anyone know the correct sized air filter for this carb and where to get it at the best price?

Thank you for the help.

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Re: Mikuni Kogyo Carb

Postby ML » Wed Jul 29, 2009 5:36 pm

Brian,
You have what is commonly known as a Mikuni VM. This is a popular conversion for the 750 and 850 Commandos replacing the original dual Amal Concentrics. The parts you show all appear to be correct for installing onto your 750. To identify the size of the VM, you have to measure the inside diameter of the manifold side of the venturi, i.e. the smaller end. This may be 34mm or 36mm or possibly 38mm. The 34 and 36 are common. 34 is a good allround performer. The 38 is not good for a stock Commando.If your motor is a Combat, the 36 will yield greater top end performance and needs to be jetted accordingly. Check the top of the cylinder head around the right hand exhaust rocker cover for a stamp C. That means Combat high compression motor & cam and 32mm intakes. An RH # stamp denotes other milder motor specs.

The air filter plugs onto the bigger end of the carb. The most popular are the KN series and they come in a variety of forms. The most common appears to be the pancake design. Measure the outer diameter of the carb intake. This measurement will need to correspond to the KN filter spec for its mounting boss. Check the KN web site or call your local British parts dealer who may have them. But, first install the manifold and carb and measure the space from the intake mouth of the carb to the frame junction. Its not a lot and select the biggest air filter you can fit in there.

I don't know the size of the Allen bolt that holds the rubber adapter flange as the alloy manifolds were made by several manufacturers and it could be UNF or possibly Metric thread. Try several that appear suitable and don't force a bolt in, it just has to screw in gently. I suspect its UNF 5/16 or 3/8.

Mick

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Re: Mikuni Kogyo Carb

Postby swooshdave » Wed Jul 29, 2009 7:57 pm

I'd say no Combat because of the drum brake.
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Re: Mikuni Kogyo Carb

Postby tpeever » Wed Jul 29, 2009 8:06 pm

brianchahn wrote:Does anyone know the correct sized air filter for this carb and where to get it at the best price?


I have a 36 mm VM Mikuni and the pancake-style filter that fits it is a K&N RC-0850. It is about 2 inches thick and is a tight squeeze but it fits. I have found that the prices buying online from K&N directly are as good as anywhere else.
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Re: Mikuni Kogyo Carb

Postby bpatton » Wed Jul 29, 2009 9:51 pm

brianchahn wrote:Question about the Carburetor that came with my 72 Norton (came in a box of parts). The only markings on it are MIKUNI KOGYO JAPAN, and MIC on the other side.
Will this be a sufficient carb for the bike?

I also have the two to one machined part, but don't know the correct size screws in the picture below. They do not seem to be the same size as the ones the other ones for that part that screw into the block. I think it might be a 7mm or something.

(second to last pic is not mine.. i got it off the net)

Does anyone know the correct sized air filter for this carb and where to get it at the best price?

Thank you for the help.


An easy way to identify which size VM you have is to look at the rubber coated spigot that attaches to the carb. The size is cast in the edge.
Image
This is for a VM36mm carb. The size is stamped on the carb body itself on the front of the choke.
Image
Their 6's always look like 5's, that way.
The screws that I have are 5/16 coarse for both. It looks like you may need vent hoses, gaskets, aircleaner, screws and washers, a new cable with adjuster, and maybe even some innards. Source it all from a Sudco dealer, or MAP.

The 34mm carb is great, it' sufficient unless you are prone to mix it up with hooligans and need every advantage you can get. But if that were the case you would probably be running dual carbs. One difference in the various VM's is the size of the carb body. The 32mm and 34mm share the same casting. The 36mm / 38mm casting is significantly larger. On my bike the 36mm wouldn't fit.
Lastly, the socket screws you mentioned that thread into the head need a specific type of washer. They are narrow and appear to be hardened.
Bob

73 Interstate
02 VFR
75 Suzuki GT750

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Re: Mikuni Kogyo Carb

Postby splatt » Thu Jul 30, 2009 2:21 am

The intake bellmouth on that carb looks abit odd doesn't it :?: :?:
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Re: Mikuni Kogyo Carb

Postby brianchahn » Sun Aug 02, 2009 3:16 pm

Thank you everyone for your help.

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Re: Mikuni Kogyo Carb

Postby plj850 » Sun Aug 02, 2009 3:42 pm

brianchahn wrote:Question about the Carburetor that came with my 72 Norton (came in a box of parts). The only markings on it are MIKUNI KOGYO JAPAN, and MIC on the other side.
Will this be a sufficient carb for the bike?

I also have the two to one machined part, but don't know the correct size screws in the picture below. They do not seem to be the same size as the ones the other ones for that part that screw into the block. I think it might be a 7mm or something.

(second to last pic is not mine.. i got it off the net)

Does anyone know the correct sized air filter for this carb and where to get it at the best price?

Thank you for the help.


Do LOCTITE!! the two Allen Bolts that the fix the 2 into 1 manifold to the head you really do not want those to loosen up.(You don't get a chance to see them if they start loosening.....not good if they do :cry: )
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