Carburetor Information
U.S. CB750 Models 1969-1978
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Bench Synchronizing Carbs
Contrary to popoular belief Bench synchronizing carbs is no more complicated than gapping plugs or setting points. Same principle. All you'll need is a very small drill bit or small diameter (1/16" works well) rod that is stiff and striaght (large paper clip straightened out works too, just make sure it can be inserted perfectly straight into the throat of the carb, a 17mm open end wrench, 10mm box end, and some patience.
Fisrt step is to situate the carbs so you can easily reach the adjusters and lock nuts shown above left yet still be able to slide your "gauge" under the slider without having to angle it. Turn the adjusters and lock nuts down until you have about 2 threads showing on the rod (again, above  left). Next pick a carb to start with adjust the idle stop screw (above right) so that the gauge just slides under the slider as shown below. I use #2 because it is directly in between the idle stop screw and spring and usually returns to the exact same spot during the process.
There is a very small notch at the bottom edge of the sliders on the engine side, and this is why I use the shank of a very small drill bit (image below). That notch is seldom marred up, but as most will find out many racks have been in the hands of Billy Joe Bob Bighammer and they've used a screwdriver or other implement of destruction to free stuck slides in the past and marred the bottom edge of the slider. Once you have that set so that the bit is just lightly snug between the bottom of the carb throat and the notch at the bottom of the slider you can move on to the rest of the carbs. Looking at it from the top turning the larger adjuster nut clockwise raises the slider, and counter clockwise lowers it. It helps to keep the lock nuts snug as you adjust but don't tighten them down yet.
After adjusting each carb and before moving on to the next raise and lower the sliders, as if you were throttling the bike and check again. Sometimes it may take several adjustments to get it just right. Once all the sliders are adjusted you can lock the nuts down (image below). Then check again. Often one will get nudged out of adjustment when you tighten the nuts so just loosen that one and readjust a bit. Make sure you hold the 17mm open end wrench in place firmly so the adjuster nut does not turn when you tighten the lock nut down. It is not necessary to mash the lock nuts down. Nice and snug is good enough. Too tight and it can bend or strip the threads and make future adjustments a pain in the rear or ruin the slider rod.
That pretty much has it. Not difficult at all, just a bit tedious and requires a little patience.


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