Carbs and Air Filter Housing Holes

[TimW]

Hi Folks,

I've been working on my carbs lately and noticed something I'm not sure about in relation to the carb and air filter housing.

Does anyone know why there are three holes on the housing and four on the carb? The two lower holes are obviously for fixing the housing, but having just one upper hole on the housing is leaving me stumped as to why. The two upper holes seem identical leading to the channel around the top of the carb body plus all gaskets I've seen have had the four holes which adds further to my confusion.

 

[nospark]

That's a good question. On (British) SU carbs they are two air rectifier holes. My understanding is that the piston (that holds the needle) has a small hole in it that gives access to the suction chamber above. This enables the piston to rise and fall. The air rectifier holes that you are querying are used to allow the piston to fall properly.

Hitachis are copies of the SU. They might have simply directly copied the two holes but found that the Hitachis did the job (or did it better) with one hole and so blanked it off with the filter housing. You might also find air housing variants with two holes depending on the particular world market.

You might find the answer on USA forums. Come back and let us know

 

[adrianf240z]

absolutely correct answer. 10/10
Adrian