Topic: What year is my CB750?

[cb750-bobber]

OK, Thank you in advance, two weeks ago I bought a CB750 bobber project, I was told the engine was a 76...after getting it wired and plumbed and running My brother and I found out that the throttle cables from his 74' cb750 wouldnt work on my "different looking" carbs..After some research on the web It appears that the bike has a non-matching set of carbs with the power plant. My case numbers read CB750E-3012064          My carbs look like the Hondamatic carbs I believe they are "a" series? In anycase should I sell these carbs and get the correct year carbs for it(bike runs fine, idles great, havent physically been ridden yet. Any info would be great.

[cb750-bobber]

[cb750-bobber]

The non bottle cap carbs

[Alan F.]

Nah, don't need to sell them, we'll get you sorted out.  

There's a guide somewhere around here for identifying carbs by casting number, but Ican't seem to find it quickly.

Here's the carb FAQ for ya.
-Alan

[cb750-bobber]

My &%) and my brothers build we're doing together...last pic!

[Ryan6838]

Look like the carbs the autos the 77-78ks and 77-78fs had. No reason to sell them unless you just like the way the older ones look. Should run fine with the newer carbs.

[cb750-bobber]

Thanks guys, I have to get the casting no. off of them tommorrow...I read online that the auto's carbs were smaller and dont created as much HP as other years*bottle caps*

[zzpete]

Heres a link for a timeline on engine numbers. Looks like yours is a 1978.
http://www.hondachopper.com/engine/engine_timeline/timeline.html

[cb750-bobber]

That being said the carbs are period correct then!...HmmMy CB is wimpy compared to my brother 74....damn!

[cb750-bobber]

THANKS Gentleman!

[Ryan6838]

Why do you say its wimpy?

[eurban]

Your carbs appear to be of the PD41/PD42 range.  These were the stock carbs for the 77 and 78 750 K and F models.  Properly functioning and setup, these carbs should provide crisp throttle response and good power.  They won't perform properly if the accelerator pump is not functioning or the if the idle circuit is crudded up. Also,  if the intake and exhaust systems are modified, they (like any of the range of 750 carbs) will also likely need main jet size changes, main jet needle position adjustments and adjustments/changes to the idle jet.  Perhaps there are carb function or setup issues resulting in your cb's "wimpy" performance?

PS: those carbs don't appear to be carbs from an automatic 750.  CB750A carbs would be a poor choice for performance as they are smaller in bore than the 28mm K and F carbs.

[Alan F.]

There are many other factors that would make your bike less of a performer than your bro's,  What about sprocket size for instance? What are the specific differences between the two bikes?

[cb750-bobber]

I cant actually say it's wimpy compared to my bro's yet, but from what I've read he's got 10 more HP by deffault..is this not true..1973 VS 1978 CB's In anycase, the carbs were refurbed by micro-bore out of Syracuse NY and once it started the throttle response was fantastic..I know they will run fine...although, not surprisingly carb #2 drips if gas is on...poor float seat..or something stupid that I could spend too much time figuring out!!! Anyone ever found pretty'd up stock hand controls for the CB750's?

[Ryan6838]

Idk if there's a difference in numbers on the carbs, thought the newer one make more but 10hp i cant see early bikes had different exhaust and tuning that made more power. Takes some work for a 68hp (think they were 68 stock) to gain 10hp.

[eurban]

I cant actually say it's wimpy compared to my bro's yet, but from what I've read he's got 10 more HP by deffault..is this not true..1973 VS 1978 CB's In anycase, the carbs were refurbed by micro-bore out of Syracuse NY and once it started the throttle response was fantastic..I know they will run fine...although, not surprisingly carb #2 drips if gas is on...poor float seat..or something stupid that I could spend too much time figuring out!!! Anyone ever found pretty'd up stock hand controls for the CB750's?

Not sure where your info comes from  . . .Your late engine has a better flowing head and slightly higher compression (9.2:1 vs 9:1) ratio.  The PD carbs if properly functioning and setup should also provide better performance.  All other things being equal, the late engine should make more HP but it won't be anything like 10hp.