Topic: seeking carb size advantage clarification

[KRONUS0100]

ok not looking to start an argument, just seeking clarification.  for the record i am happy with the stock 750 carb/stock air box set up.  just a couple questions

1.  if stock carbs/airbox work, why change?  jet changes work for most mild mods like cam or exhaust
what size are they in mm?

2. on the 77/78 750F models there is an accelerator pump................generally these are the better carbs.  what size are they in mm?

3.  have seen posts about CR's, GSX and CB650SC carb swaps, as well as Kawasaki Z1 style carbs.....cant run air box, must run pods or similar................again what size are these carbs

4.  what advantage do the Z1 style carbs have over the stock 77/78 F carbs?

5.  lastly, i have been told the 750A carbs are smallest of the bunch, but dont know never have seen any up close off the bike, advantage here?

[bjbuchanan]

I'm gonna go out on a limb with the 750A carbs but if they are smaller it is probably due to the fact that it is an automatic. Probably some type of vacuum reference and also it is generally easier to get an automatic to idle with the smaller carb throat if they use vacuum reference for shift points and firmness

Later model style carbs like GSX and stuff can be a different type of carb that doesn't need the airbox to equalize pressure and turbulence to the four diff carbs. As such, you can run the pods easier on them without the same tuning issues

[lucky]

You said,  "2. on the 77/78 750F models there is an accelerator pump................generally these are the better carbs.  what size are they in mm?"

I do not know why you think these EPA I carbs are better.  Restricted.
They cannot really be worked on until you take them off of the motorcycle.

the CB750F was the stingiest of all the carbs. EPA type II   Severely Restricted.


The stock 1969 carbs produced the most power of all the CB750 SOHC's.
Easiest to work on while on the motorcycle.
No throttle shafts or "lifter arms".
The 69 carbs had a simple clips holding on the float bowl. No tiny screws.
You can easily adjust every single adjustment while the carbs are on the bike.


The larger the carb the better the low end torque.

[KRONUS0100]

iwas thinking that the accel pump were smoother when you rolled on the throttle or goosed it hard.

i did not know that about the 69 carbs.

[Xnavylfr]

KZ carbs= came with 26mm,28mm,29mm. the 26/28 are pretty much standard carbs. BUT the advantage on the 29mm was there is a 17mm plug in the bottom of the carb bowl so you can change the main jets WITHOUT removing the carbs from the bike. VERY sought after by drag racers because they can rejet  between runs without taken the whole bike apart.  IF you can  find some 29mm MIKUNIS  you WILL pay dearly for them. About 500$ for a GOOD set!!


Xnavylfr(CHUCK)

[bjbuchanan]

The advantage of having an accelerator pump is that you can tune your idle to be a good air/fuel ratio, not on the rich side and also have extra gas when you goose it

In order to mask a lack of accel pumps you gotta have overrich idle tune so the engine doesn't starve with a fast twist of the throttle. That is why most of our bikes have to run a little on the rich side. Not pig rich but a little more so than a later 77-78 carb