Topic: Can someone explain what the carburetor passage plugs is/does?

[77CB750K]

1981 CB750K with 33K miles.

Can someone explain what the purpose of carburetor passage plugs are?

What is the purpose of that carburetor port if it is plugged up with a little black rubber plug?

Are the passage plugs necessary?

Thank You,

Rod
Oriental, NC

[wannabridin]

which ports are you talking about specifically??

[Tugboat]

I assume he means the pilot jet port that has the rubber plug in it. I've actually wondered this myself and will be interested in the answer...

[77CB750K]

Yes...pilot jet port...beside the needle jet and idle jet.

Rod

[77CB750K]

I took the carbs apart and made the mistake of soaking the four passage plugs in carb cleaner for two minutes because they were cruddy.

Not one of my brighter moments.

They all got a little mushy.

I just ordered a set for $10.00 but wonder if they are necessary.

Rod

[mystic_1]

They are necessary.  The only reason that plug is removable is so that you can access the slow jet.  In operation, the vacuum in that passage draws through another passage that's at a right-angle to the plugged one.  Pull the plug and look inside and you'll see the hole in the side of the passage.

There are very few "optional" parts in your typical carburetor

mystic_1

[Green550F]

Yep it's needed! Like all jets it meters an air fuel mix, but it's fuel source isn't the pool of gas below but instead from the passages. Now we still have to put a jet in there and then seal it up right? At this point a rubber plug is #1-Cheaper than a srew in plug, and #2-Faster to install while manufacturing. In all it is a cost saving thing... And we all like to keep the cost down on carburators! (e.g. rebuilds vs replace)

[Vintage Hondaman]

I agree that the passage plugs mentioned are a requirement on a 750 machine.
 I am restoring a 1982 Honda Nighthawk SC  650 , originally imported from the USA. Despite much research I cannot find any information to confirm that the Keihin VB carb fitted to my bike should have the rubber passage plugs fitted - the bike will run without the passage plugs fitted , but the 4 idle mixture screws mounted external to the float chamber do not change the idle speed or tickover quality when I turn these in or out . The spark plugs are firing well , but they are quite black , indicating a rich mixture ? I have installed 4 passage plugs in after seeing the black spark plugs -and now the engine will not start or run , I have checked valve clearances and syncronised the carbs (when the bike was running that is ! )

Should this Carb have the passage plugs installed ?   All help appreciated !