Topic: Sorting through carb adjustments

[DaveInTexas]

I will make it quick and dirty as I realize it is pretty complex. 
Submitted for your corrections:
(I have all the books and have read all past posts, I just need to write it all out in a logical order, so I understand it!)

For 'my' carbs (I understand there are different brands, mine are original  1970 CB750 carbs I believe)

Idle:
Fuel - set with the Idle jet (a fixed orifice)
Air - set with the "Air Screw" (flat head screw on an angle, side of carb)
RPM - set with the Idle stop (thumb knob at 90d to carb orientation, out the side same side as Air Screw)  Has a 'T' on the stem.


Mid-speeds
Fuel - set by depth of needle that enters larger, or High Speed Jet; so the throttle position
Air - Throttle slide permits air, no other 'adjustment'.

WOT (full throttle)
Fuel - size of high speed jet (presumably some fuel also enters via the low speed jet)
Air - Bore of carb throat as the slide is out of the way completely.

Other:
If the float level is too high, expect over-rich condition at idle and maybe low speeds.
If the float level is too low, expect fuel starvation mostly at high speeds

The individual throttle cables (for the "4 into 1 cable" like mine) must be set to the same tension when the throttle is released and the slides on their stops.  Otherwise they will not all open evenly.


What else?
What corrections?

[TwoTired]

Don't know how much detail you want.  But, the air catagory is incomplete.

Both the slow system and throttle valve system have air jets located at the mouth of the carbs.  These are drilled holes with fairly crude calibration.  Anyway, the slow system's air bleed adjust further restricts air from this jet for use by the slow jet emuslion tube (the small tube with the cross drilled hole.  The emulsion tube froths the fuel from the slow jet before it gets to the carb bore,  At idle there is still air getting past the slides in the carb throat as they are not completely closed off.

The main throttle valve also has an emulsion tube to froth the fuel with air from it's air jet before entry into the carb throat.

When cleaning, the air jets should be checked for flow, too, as well as the passagways to them.

Also, the slide needle fits into a needle jet at the end of the emulsion tube.  Midrange mixture control.

Cheers,

[DaveInTexas]

Cool!
But the remainder of what I offered up is....close?

I was mainly interested in things that can be readily adjusted.

[eurban]

In the low mid range or high idle range the shape of the slide cutaway has a pretty significant impact on the mix.  For serious carb tuners like racers changing the slide cutaway  (cut out portion on the slide piston) is another tuning step.  Richer/leaner parts are available for many carbs but I wouldn't know where look for parts to fit stockers. Creative grinding and or building up might be the only option.  Also In addition to adjusting needle clip position for mid range fuel control needles are often times available with different profiles which vary the length and width of the taper and perhaps even possessing multiple taper angles.  Again these parts don't seem to be readily available for the stockers but a serious carb tuner might find a way. . . . . . . .

[TwoTired]

But the remainder of what I offered up is....close?

I was mainly interested in things that can be readily adjusted.

Yes, you are on the right track.

Float levels, control the amount of fuel stored in the carb itself.  Low levels will make the entire operating range lean, high levels tend to make them rich.

Why?
Low fuel levels require a bit more pressure differential to draw the fuel up the slow jet, to premix with air before delivery to carb throat.  Your carbs have an air bleed adjustment to compensate for this, though.

However, the froth level in the main throttle valve emulsion tube, is effected by the fuel level in the float bowl too.  This would effect the entire midrange and WOT throttle positions, too.

Cheers,