CB750 Carburetor Cleaning
Holidays are busy for everyone, and that’s true here at RestoRevival, too. I haven’t done any work on the CB750 for weeks. I did however meet with Matt last week and we finally got his ignition switch! It took about three weeks to get here as we found it in Malaysia, but it’s here and ready to go in. Will post pics on the progress there when we get in plugged in.
In the meantime, I took some time today and got working on the CB750 carburetor cleaning. Here are some close up shots of the step by step, and some old school “photoshop” so you know what parts you’re looking at…
Let’s start with the whole bank of carbs.
Carbs off, ready for cleaning
You can see upon closer examination that there is already some gunk buildup in the ports of the carbs. I’m expecting this to be a dirty job.
Gunk
So let’s get these puppies apart. First remove the carb bodies from the backing plate via the 8 screws. This is what you should get:
Separate from backing plate
Then disconnect the choke linkage by removing (carefully!) the microscopic cotter pins. Be sure to put them back or store them in a clearly marked place, or buy new ones.
Cotter pins? You mean THOSE little things?
Four breaks down to two, then down to one by separating the vacuum lines and fuel tube joint. Next you can unscrew the cap and remove the throttle valve assembly. Pop off the bowl and see how much crud you have inside.
Crud
Enough to plug the drain screw? Perfect. Then you can assume your idle/slow jet is restricted or plugged, too. Good thing you’re patient and it’s too nasty outside to ride anyway. Once you’re done gawking you can unscrew the idle jet, main jet, float, float valve, and float valve seat. Inspect these for more crud.
Old School Photoshop
Now you can move on to the idle air screw and spring and the vacuum plug screw. Oh, be sure to not lose any of these. You have my permission to copy my handy dandy labeling techniques if you too find it faster than photoshop.
I used adobe Illustrator for this one.
Lastly would be to disassemble the throttle valve assembly, carefully. If the screws holding the jet needle set plate don’t want to come out easily, don’t force it. They’re likely gunked up too.
Small screws = easy to round out.
Flip it over and spray a tiny bit of penetrant into the hole where you can see the threaded tip of the screw (no picture for this step).
Now that you’ve got it all apart, the next thing to do is actually clean it. Then put it back together the way you took it apart. That will be for the next post…
RestoRevival 
awesome old-school photoshopping. big fan!
Great articles and pics! The pics really made a whole load of difference! Lots of words make my head spin.
Fantastic i have been trying to sort my carbs and this is the best thing i have come across well done hope i can find part 2 thanks Bobby.
Do you have an y of the assembly instructions. I am having a hard time figuring out how to insert the metal piece that attaches to the throttle rod into the carb with the choke flaps. can’t get the lever to line up with the choke flaps and still get it to connect to the throttle arm.
In other words, i can’t connect the throttle rod to the choke flaps (inside the carb slot).
Hi Martin, I kinda fell off the face of the planet there for a while. Thanks for your questions. I’m sure that you have figured out how to put those carbs back together by now, but to answer your question none the less. The short answer I have is that I did not take the throttle rod and choke flaps apart. I left all that together and dismantled the lower half of the carbs only. I soaked the entire upper assembly in a can of carb cleaner overnight, along with all the small parts from the rest of the carb body. Then scrubbed everything with a toothbrush and dried them with compressed air before reassembly. I’m afraid I can’t help much with the specifics about the choke flaps.