Topic: 1978 750k carbs vs. 1974 750k carbs?

[Dunstall_74]

I just picked up a 1978 cb750k with the newer style carbs (the ones with the top plate that's held down w/ 3 screws).  I have a set of early style cb750 carbs laying around that I rebuilt for a 1974 cb750 that I used to have.  I am tempted to just slap on the rebuilt carbs that I know are ready to go, but before I do.........Does anyone know which ones are better performance?  I'll be running the typical pods/4-1 header setup.

[eurban]

You will need a set of the earlier intake rubbers if you want to run the earlier carbs.  Both carbs types can be made to work well.  The late carbs are a bit more of a challenge to get clean but IMHO are a better performing carb set when in top nick.  The accelerator pump is nice feature.

[BobbyR]

The 78 carbs have an aacel pump which you will find very useful when you change throttle positions quickly. It helps reduce engine boggong greatly.

[lucky]

I disagree.

The first CB750's had the most power ,were the easiest to work on and adjust.

Since then the CB750 carbs have gotten worse and worse.

The later ones have complicated mechanical linkages to operate the slides.
To  change slide needles takes hours.
On the 69-70 cb750 carbs it could be done in minutes. Not kidding.

The adjustments on the early carbs were easy to get to.
The choke was a lever you just flip up or down. NO CABLE!

The 1977-78 carbs had the accelerator pump and spray jets but when trying to tune the carbs you not only have to get the idle jet correct,the main jet correct and the needle correct but then throw in the WILD CARD of the accelerator pump too!

The 1978 had non adjustable needles making that hard to deal with and the push in idle jets which was just another road block to tuning your carbs.

The 1977-78 carbs also had the air box act as a giant choke limiting the intake air significantly.


Look on the internet. You will not see lots of entries about the early carbs being hard to deal with.

But there is NO ONE that has a solution for the 77-78 carbs to run pod filters.
No One has the answer. Other that put the stock air box back on and then if you have aftermarket exhausts it is still a problem child.

I can give you one suggestion though. Start looking for some 1977 adjustable needles for your 1978 carbs if you still want to run them. You will need it.

[BobbyR]

The 77-78 carbs are not very complicated. You have cables that attach to a wheel that is attached to a shaft. They all open all the way as a group and they close as a group.  No multiple cables to adjust. The accel pump was on cars decades before the CBs cam out. They were put there to prevent bogging.

What Honda did not design for, was people sticking aftermarket this and that on the engine. The airbox was designed to gather quiet air so the carbs would have a predictable vacuum.

If you look at it the accel pump is the Podders best friend by enriching the mixture when you roll onto the throttle.

When you modify a bike you should be prepared to work on it to make it right. It is not the manufacturers job to do that.

Honda went to expense to design and have  it manufactured. They could have stuck some pods on there for probably less than a buck a piece.

[SOHC Digger]

I'm not saying one style is better than the other, but I am a fan of the 77-78 PD's.

And the needles on these can be changed in minutes too.  I'd even say they're easier to change than the earlier round-top style.

[bollingball]

I feel sorry for lucky he never did figure out how to work on the pd carbs. I don't think they could be any more simple. Great carbs The 74 carbs are also good carbs. It is easy when someone does not understand something to blame it on any thing but ones self. Clearly Honda did not plan for lucky

[ZanVooden]

Yep. Another vote for the late model carbs. I have a set of each and throttle response on the later carbs is so much better because of the accel pump. I've never had an issue with working on them either.
Yes one downside is the screw on bowls rather than the clip deal on the earlier carbs, but its not that big of deal.
Run them the Honda intended, and the way they were engineered for, and they work great. If you want performance get a set of CR carbs.

[bollingball]

The CRs are nice but you really need a built motor to justify the cost. They would be over kill on a stock motor. IMO But damn they are pretty

Ken

[lucky]

I'm not saying one style is better than the other, but I am a fan of the 77-78 PD's.

And the needles on these can be changed in minutes too.  I'd even say they're easier to change than the earlier round-top style.

You must have never changed needles on those early Honda carbs.
You just walk up, unscrew the top of the carb and out pops the entire slide and needle. NO TOOLS NEEDED.
Same with the float bowl. undo the clip and the float bowl is off .
NO TOOLS NEEDED.


The 1977-78 carbs you have to undo two phillips screws for the carb top and then loosen the 8mm nut holding the pivot arm onto the shaft so that you can rotate the arm far enough to get the slide out.
OR you can leave the slide in and try to get the two screws on the needle holder loose down inside the slide and not drop anything.

I know because i have done BOTH.

BTW...The 1978 model does not have an adjustable needle. Another problem.

[lucky]

The CRs are nice but you really need a built motor to justify the cost. They would be over kill on a stock motor. IMO But damn they are pretty

Ken

Yes...I would love to have a set. Completely adjustable.
No bull. No accelerator pump.

[BobbyR]

I'm not saying one style is better than the other, but I am a fan of the 77-78 PD's.

And the needles on these can be changed in minutes too.  I'd even say they're easier to change than the earlier round-top style.

You must have never changed needles on those early Honda carbs.
You just walk up, unscrew the top of the carb and out pops the entire slide and needle. NO TOOLS NEEDED.
Same with the float bowl. undo the clip and the float bowl is off .
NO TOOLS NEEDED.


The 1977-78 carbs you have to undo two phillips screws for the carb top and then loosen the 8mm nut holding the pivot arm onto the shaft so that you can rotate the arm far enough to get the slide out.
OR you can leave the slide in and try to get the two screws on the needle holder loose down inside the slide and not drop anything.

I know because i have done BOTH.

BTW...The 1978 model does not have an adjustable needle. Another problem.

OMG I never realized how bad I had it undoing those two Phillips head screws every time I synch the carbs.

The float bowl screws can and should be swapped out with hex heads. I know it takes tools but the Nuns taught me I was placed on this World to suffer. That is why the Lord put a 78K in my lap.   

[xsmooth69x]

ow thank god a bought a 1972 

[lucky]

I'm not saying one style is better than the other, but I am a fan of the 77-78 PD's.

And the needles on these can be changed in minutes too.  I'd even say they're easier to change than the earlier round-top style.

You must have never changed needles on those early Honda carbs.
You just walk up, unscrew the top of the carb and out pops the entire slide and needle. NO TOOLS NEEDED.
Same with the float bowl. undo the clip and the float bowl is off .
NO TOOLS NEEDED.


The 1977-78 carbs you have to undo two phillips screws for the carb top and then loosen the 8mm nut holding the pivot arm onto the shaft so that you can rotate the arm far enough to get the slide out.
OR you can leave the slide in and try to get the two screws on the needle holder loose down inside the slide and not drop anything.

I know because i have done BOTH.

BTW...The 1978 model does not have an adjustable needle. Another problem.

OMG I never realized how bad I had it undoing those two Phillips head screws every time I synch the carbs.

The float bowl screws can and should be swapped out with hex heads. I know it takes tools but the Nuns taught me I was placed on this World to suffer. That is why the Lord put a 78K in my lap.

Syncing them is easy.

[lucky]

ow thank god a bought a 1972 

Still not as good as a 1969 or 70 but much easier than the 77-78's.

[754]

 The flattops are bettewr for fitting custom tanks..need no up clearance.
 If modding your framerails, as in changing location, they will clear the frame, the earlier ones will not..

[xsmooth69x]

ow thank god a bought a 1972 

Still not as good as a 1969 or 70 but much easier than the 77-78's.

for the price of a 69 or 70 u couldve probably bought 10 of my bikes