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I recently traded some art for a 1978 Honda Hawk CB400 (TI - I think). It has been sitting for years, and much of the bike was disassembled in a Tubberware container, along with water, thus much rust and corrosion.

Upon looking into the carburetion, taking apart what I could manage through the rust, I noticed that this specific carb does not have a rubber diaphragm but a steel one. This carburetor is also double butterfly valved; later models seem to have been installed with carburetors containing only one flap per carb.

Firstly, could someone identify by technical name these two types of carburetors: what's the name for the steel-diaphragmed carbs, and what's the name for rubber-diaphragmed carbs? Are these both CVs?

Secondly, what is the purpose of having 2 butterflies per carb, and is it necessary for this particular type of CB400 to run?

Third, if I chose to go with a newer set of carbs with the same mm size engine inlet hole, could this be a sustainable upgrade as far as performance and durability goes, and what, if any, obstacles would this set up for me?

Thanks,
YV
 

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Welcome to the forum. Great to see another 400 series here. Got any pics of it?
Both rubber diaphragm and aluminum are Constant Velocity carbs.
You should have a VB21 carb with a 32 mm venturion your bike with one butterfly for the choke valve and one for the throttle position. This carb was used for 78 and 79 400's.
You can use VB22's on the bike which have a 30 mm venturi and an accelerator pump. (used on 80 to 86 400's)
 

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There have been a couple of people working with the Mikuni VM series carbs, Haven't seen any updates on they're progress for awhile. Lots of complaints to be found on the internet about the stock carbs but I've found that with careful attention to detail in cleaning and assembly they are just fine. Plus by using them we can give support whereas the Mikuni route you're the expert.
 
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