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Author Topic: CB250K4 carburetor puzzle  (Read 245 times)

Offline madsundaysurvivor

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CB250K4 carburetor puzzle
« on: February 11, 2026, 07:23:06 PM »
Good night, I introduce myself, it is my first time in this forum. I have several Hondas from the 70s.

 Now I am checking the carburation of a 1974 Honda CB250K4 and seeing the condition of the carburetors (different vacuum springs, different main jets and no number) I would like you to confirm the correct size for primary and secondary main jets. and also how can I identify the correct spring vacuum for my model

thank you for your attention
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Offline Bryanj

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Re: CB250K4 carburetor puzzle
« Reply #1 on: February 12, 2026, 01:25:13 AM »
Those are questions for the Honda Twins forum, also try comparing parts at cmsnl BUT make sure you look at the correct country parts as they may well very between countries
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Offline AshimotoK0

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Re: CB250K4 carburetor puzzle
« Reply #2 on: February 13, 2026, 03:48:01 AM »
Firstly check you have the correct carbs as they often get fitted with earlier ones.They should be 725B. Spring wasn't available as a separate part ...it comes with the diaphragm / piston assembIy...I would probably assume it's OK unless someone has changed the diaphragm to a 350 one...as I think 350 diaphragms assemblies are different .... I will check on my parts books for you and reply again.
« Last Edit: February 13, 2026, 04:26:40 AM by AshimotoK0 »
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“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.

Offline AshimotoK0

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Re: CB250K4 carburetor puzzle
« Reply #3 on: February 14, 2026, 01:02:12 AM »

CB250K4 UK Model.
Main Jet: #105 (Standard) or #110 (often listed for England models)
Main Jet Primary (small nozzle): #70
Slow/Pilot Jet: #35
Needle Jet: #D207

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“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.” Grace Slick, Woodstock '69 .. In the year of the Sandcast.
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