Topic: Carb sync question

[acollin]

1974 cb 750 stock set up and mostly stock set up1972 cb 750 ( aftermarket 4 into 2 exhaust).

I bought a "Carbtune pro" a few years back and it has been super to use on my 1974 cb 750. I recently purchased a 1972 cb 750.

I have synched the carbs on the 74 and believed I was successful. Great idle-- nice excelerations-- great range-- no barking-- hiccups--I'm very pleased.

I've been working on the 72 and in preparation to synch the carbs i re-read
the procedure in the Carbtune pro manual and it states "remove and blank off any balance pipes."

I never did this on my 1974. I assume the balance pipes are those small horizontal pipes joined by plastic/rubber hose tubes. I supposed they could be clamped.

My question is: are my carbs synched if i did not " blank off the balance pipes"? Do I need to blank off the balance pipes to synch the 1972.

Thanks for your thinking and assistance

[70CB750]

I think the balance types would be a way to equal the vacuum in carburetors, you don't want that while balancing.

Is it possible the Carbtune is universal tool and this particular part does not apply to SOHC4?

[Dream750]

I think the balance types would be a way to equal the vacuum in carburetors, you don't want that while balancing.

Is it possible the Carbtune is universal tool and this particular part does not apply to SOHC4?

70CB750, I think you are on to something here.

Balance pipes are fitted to some Amal carb models used on twin cylinder Triumph and Norton bikes. These balance pipes connect the carbs. They need to be blanked off before performing a carb sync. That’s the way I read the Morgan instructions, perhaps a British bike owner can confirm this. 

[acollin]

The quote did come as part of their generic discription, but wouldn't balancing/synching the carbs require measurements from all carbs at the same time?

Is this possible if they are not connected in some way?

What would they be balanced to or synchronized with?

If as you suggest the balance pipes need to be blocked off, how do I explain the success of my attempt to synch the carbs when I did not block the balancing pipes?

Thanks for the help, but I am still confused.

[lucky]

The entire post is confusing.
What motorcycle are you working on? NOW.
Balance tube on Carbtune or motorcycle carbs?

Are all other tune up items taken care of?


Carbs come last.

[70CB750]

The quote did come as part of their generic discription, but wouldn't balancing/synching the carbs require measurements from all carbs at the same time?

Is this possible if they are not connected in some way?

What would they be balanced to or synchronized with?

If as you suggest the balance pipes need to be blocked off, how do I explain the success of my attempt to synch the carbs when I did not block the balancing pipes?

Thanks for the help, but I am still confused.

IMO you dont have any balancing tubes.  Since you were able to balance the 74 you satisfaction, do the 72 the same way and be happy

[Dream750]

Thanks for the help, but I am still confused.

Sorry for the confusion.
 
The intent of my reply was to clarify and define the terminology “ balance pipe” as used by Morgan.
 
The balance pipe term refers to Amal brand carbs used on British bikes as they use a balance pipe to connect the carbs for the purpose of equalizing carb vacuum.
 
This has nothing to do with exhaust balance pipe connector found on a 750 four with stock exhaust.

Your stock 750 Keihin carbs do not have a vacuum balance pipe and this is a non-issue.
 
Sync your 1972 carbs the same way you did on your 1974 carbs and you will be just fine. No worries.
 

[acollin]

Thanks all for the reply and dream 750 for the clarification and direction.

In re-reading the Morgan manual, it would have been really helpful if they had tucked the word" exhaust" somewhere in the sentence I quoted earlier for the rookies.

Thanks again