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Author Topic: CB400F carb ports  (Read 951 times)

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Offline Keith64

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CB400F carb ports
« on: July 12, 2017, 06:12:18 PM »
What are the two ports circled in red for? Do they go anywhere? I tried blowing carb cleaner up them but it seems to just shoot back.

All the other circuits are blowing clean.

Thank you!
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Offline TwoTired

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Re: CB400F carb ports
« Reply #1 on: July 12, 2017, 09:41:43 PM »
One of them should go to the vent tube rails, I think.
That's the outside air pressure source that pushes fuel through the jet.
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Lloyd... (SOHC4 #11 Original Mail List)
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Offline Bodi

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Re: CB400F carb ports
« Reply #2 on: July 13, 2017, 04:18:06 AM »
I think these are dead end holes, that they are for the feed from the fuel inlet to the float valve - the left set is finished and the right set is not. The carb bodies are cast ambidextrous, things can be finished on either side and left unused on the other. One circled hole looks as-cast and not drilled (the top one) and the other appears to have a plug driven in at the bottom. Atmospheric vent is through the overflow tube. I can look at a rack later but I think one of the holes at the very top of the cavity connects to the balance vent, the little tubes between bodies.
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Offline Keith64

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Re: CB400F carb ports
« Reply #3 on: July 13, 2017, 10:49:17 AM »
Quote from: Bodi on July 13, 2017, 04:18:06 AM
I think these are dead end holes, that they are for the feed from the fuel inlet to the float valve - the left set is finished and the right set is not. The carb bodies are cast ambidextrous, things can be finished on either side and left unused on the other. One circled hole looks as-cast and not drilled (the top one) and the other appears to have a plug driven in at the bottom. Atmospheric vent is through the overflow tube. I can look at a rack later but I think one of the holes at the very top of the cavity connects to the balance vent, the little tubes between bodies.

Thanks, that makes sense. Yes looks like on the left set of carbs the left holes are used, right holes are used on the right set.
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Offline Bodi

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Re: CB400F carb ports
« Reply #4 on: July 13, 2017, 06:42:16 PM »
I have CB77 carbs that are really odd. Keihin used something they called a "power jet", it's nicely described in the service manual - apparently no main jet was quite right so they used one slightly lean at WOT and had this extra jet that added fuel from 3/4 to full open. I have a few carb sets.. the 1966 version castings include all the oddball passages around the inlet side but nothing has been machined. A 1967 set has none of that unused stuff cast in. I have looked for a few years at swap meets and wreckers and never seen a set with the power jet stuff finished. I don't know what year they deleted it. Or how they tuned around losing it...
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