Sunday, May 27, 2007

Carb Rebuild

Picked up two carb kits for $25 each, and the correct main jets for another $6 each, for a total of $31 per carb. Now, instead of topping out at fifty-five, I'm shifting into fifth at fifty. She makes sixty at just about 5900 rpm, seventy at about 7k. Acceleration is better too. Hot damn.

Right Carb

The rebuild kit for one carb. Had to buy a separate main jet as the one in the kit was 115, and I needed 105. Not that I would've known that, but Charlie hooked me up.

Disconnect the air filter, throttle cable, and choke linkage. Remove the carb, stuff a shop towel in the intake to keep anything from getting in.

Removing the diaphragm/slide assembly (after removing the top cover and diaphragm return spring).

Removing the float bowl.

A view of the float bowl, floats, jets.

Removing the primary and secondary main jets and the holder. Just pull on them with your fingers.

Main jet holder, needle jet, primary and secondary main jets. To remove the main jet holder and the needle jet which are under the primary and secondary main jets, you reach down through where the diaphragm/slide assembly was and press them out with your finger or a toothpick.

After removing the above.

Pressing the float assembly pivot pin out with a toothpick.

Removing the float needle.

Unscrewing the float valve seat retainer clip.

Not shown: remove the float valve seat by grabbing it with needle nose pliers. I used a shop towel to protect it from the pliers. Then remove the 'pilot jet' which turned out to be just a little rubber plug. Under that was the slow jet which just unscrews. I don't know why Clymer's says to push out those two, because there's no pushing involved. Also remove the idle mixture screw and spring, and the float bowl drain plug. Then use a pair of needle nose pliers to reach down inside the diaphragm/slide assembly and compress the retaining clip. Just grab one side and pull in inwards instead of trying to grab both at once. Remove the clip, the little plastic piece, and the jet needle. Hit everything with carb cleaner and compressed air. Make sure to spray through all the little holes and passageways in the jets and carb body. Carb cleaner is nasty stuff, so if you don't have goggles use the safety squint.

Cleaned up, in the process of being reassembled.

Measuring the float height.

Pilot jet.

From top left: needle jet retaining clip, a silver thing and washer that I didn't end up using, main jet holder, primary main jet, o-ring, needle jet, secondary main jet.

The jets before pushing them in.

The hard part is over.

Jet needle retaining clip after bending it to match the old one below it, plastic thingy, jet needle.

Reassembled diaphragm/slide assembly.

View inside the diaphragm/assembly. You can see the plastic thingy and retaining clip.

Float bowl and new gasket. Didn't bother with sealer.

Putting the diaphragm return spring in after putting in the diaphragm/slide assembly.

Nice clean carb back on the bike. It did leak gas through the overflow at first, but hammering on the float bowl with a screwdriver managed to unstick the float.

Left Carb

A view inside of the main jet holder and the needle jet poking up. They're to the left of the butterfly valve in this shot.

Inside the float bowl. Note which side/hole of the primary and secondary main jets is facing out.

Cleaned and reassembled.


  1. Hey Darth.

    I'm glad I found this. I just rebuilt my carbs (72 cb350.) I believe the carbs are identical to yours. I used the same kit, and couldn't find a place for the "little silver thing and washer" either.

    I didn't use a manual, I just tried to figure it out. Now I have a leaky carb on the right side. I suspect it's the gasket because when I saw the gaskets that came with it, I assumed they gave me the wrong ones, because they were round, and not the pentagon shape of the float bowl.

    Was I supposed to just force the circular gasket to conform to the pentagon shape?

    I ended up using my old gaskets that were in it, because they were the right shape, although they both were torn.

    I appreciate any help you could give me.


  2. Nice writeup, Thanks for the info!

  3. Great job! Thanks for the help. Just completed a successful carb rebuild.

  4. Well done I do lots of these but you did a nice job.

  5. That`s great man. I have 1968 cb 350, but i dont have the original carbs. Im looking for that carbs. Anyone can help me??



  6. Thanks for the detailed pictures, this will surely help when I tackle my carbs. Charlie's Place did all the maintenance on my bike for the previous owner of my bike and I have the same air filters on my bike. Have you found that this effects your air-fuel ratio? and did you have to adjust your carbs because of this? My bike would only run w/ choke on so I decided to clean carbs... but i thought it might also have something to do w/ the air filters throwing everything out of whack...

  7. Need carburetor help! Trying to clean a carburetor on 1970 Honda CB350. Having trouble getting what I think is called the "Needle Jet". I just can't get it to come out. I'm worried that I'm going to damage it if I fiddle around with it too much trying to force it out with needle-nose pliers. I sprayed carb cleaner on it and left overnight, but it's not budging. Any advice? Can I just bang it out and go buy a new needle jet to replace it with? Do they sell them individually or do I need to buy a whole kit? All other parts are in workable condition. Thanks!

  8. where do you buy the o rings....Honda prices take your breath away.... John

  9. What air filters did you put on that? I have a 73 and want to do the same switch.

  10. Dude. You're Awesome. Thanks for posting this.

  11. Hello Great post, I recently "restored" a 1973 cb350. Today on the way into work, i was going about 55mph, and out of the blue, just started to loose power, I'm thinking the carbs need to be cleaned or its running too rich from the new pod air filters similar to your i also have installed.

  12. Hello just picked up a 1970 cb350 my carbs might be bad because it drops fuel out the bottom of the bowls. thought it was the floats stuck, had someone check them. any recomendations? Nice bike btw looks clean!!!!!

  13. Nice post! I was rebuilding the carbs on a friends 68 CB350 tonight and took lots of pictures. I had intended on posting them on my site but I don't think I could do better than you've done here. Keep it up!

  14. Are you serious, pressing the float assembly pivot pin with a tooth pick. I'm hoping this is the case becuase mine appears to be wedged in pretty good. Any advise on how to get this out. Mine is off a Carb for a 67 CB350 but the carb design is almost exact, might even be the same. Thanks man.

  15. Hey! This has been really helpful with my 1970 CB350 project. But I ran into a problem with the float bowl gasket. It seems to be large for the application. I was wondering if you had any problems with the gasket?

  16. Nice post, very helpful. Although I think the photo you have labeled "Pilot Jet" is only showing the gasket that goes behind the Pilot Jet. The pilot jet unscrews and should look something like this:

  17. This is a great post! I have a 71 with the same carbs and I have just rebuilt them but there is one thing I cannot seem to figure out. Is there supposed to be an O-ring under the spring of the air mixture screw? Does yours have that? The Honda Microfiche for that carb shows one. I am having low RPM hesitation which leads me to believe that it is coming from that portion. Any idea?


  18. HI ,i got what i think is a cb350E..the frame #says cb3503000071 an the engine # says cb350E30000079 im not sure but it looks like the numbers on the engine were changed,,how do i know if the carbs belong with that engine and what year is motor?

  19. Great article! I'm a home mechanic and this gave me confidence to do it myself. My 350 k3 carbs were straight stuck after sitting in the hot warehouse for a year. It wouldn't fire at all. Now I'm running down the interstate at 80. This picks up where Clymers and leave off.

  20. Hello..I have a 72 cb 350 twin ..doI need a 105 main jet or a 115 jet..?? thanks

  21. Thanks for posting this info. This summer on a whim I purchased a 1970 Honda CB350 from eBay. Now I get to tinker with a motorcycle that's nearly as old as I am.

  22. Hey,
    Since the jet sizes are totally different from the '68 (which this kit is made for) to the other years, does the needle work still? I can't find anything that says if they use the same needle for all years or not, and after trying to put a #115 where a #105 was supposed to go, and having to order new jets, I'm hesitant to put the needle in. Also, does the needle just click into a single spot, or does it have adjustments? I've heard of people shimming when they mod the pipes/filters...
    What tool do you use to take the needle out/put the needle in? I can't find anything on that, either, and I really, really, really don't want to mess up my bike.


  23. Hi, Absolutly Great Post. It helped me a lot to figure it out. Thank you for taking the time to give out this absolutely necessary information.

  24. the only detail you are missing is what the float height is supposed to be and what's the trick to holding it correctly to get that measurement correct?

  25. Darth, I've been recommending this write up for anyone wanting to dig in with a first time CV carburetor rebuild. With the pictures it's a great walk through!

    To answer some of the questions by the others:
    The 5-sided float bowl gaskets by Sirius:

    The air filters in the pictures are called "pods". I recommend the stock air filters, but the pods are easier to maintain and *much* easier to put back on.

    If fuel is running out that bottom shaft (oveflow drain) your "floats" are adjusted to high. As the fuel fills up in the float bowl it lifts the floats which then shut off the fuel to the bowl once it reaches a certain height. That bottom shaft is to dump out an overflow in fuel.

    @njdnjdnjd when I experienced a loss of power like that it was from a broken needle. If the bike idles fine, it's either the needle or something blocking the "fast jet".

    For a stuck needle use DW-40, liquid wrench or SeaFoam like product. Let it sit overnight in a room temperature environment. Also, a gallon can of Chem-dip parts cleaner might also help. Worse case scenario: 1. remove everything from the float bowl including jets 2. remove carb top and spring, 3. remove the needle clip and plastic thingy, 4. use small enough rod to push on the needle from the bottom of the carb.

    Needles, needle clips, o-rings and gaskets are easier and fairly cheap to replace. The rubber diaphragm is *NOT* cheap to replace.

    You have an air leak. The reason you have to put the choke on: too much air is already getting into the carb. With the bike idling spray short bursts of starting fluid at the carb. If the engine revs up, you've just found where your air leak is.

  26. thanks for the write up bro! lookin forward to rebuilding mine!!!!

  27. A couple of thangs about the rebuild that was not mentioned. Dont throw away the passage plug for the main jet (its a little black plug). Also who knows what the aluminum thingy is for with the carb rebuild kit? Also, Also....when the float bowl is removed on one side of it is a little tab that covers a small platic piece on the carb body. Undernieth that plastic piece is some hols for gas to flow through. What are those called and where can you get them, and is the aluminum piece in the carb rebuild kit to replace that?

  28. If running an open pod filter and aftermarket exhaust what key parts are needed ehen doing the rebuild.
    (71 Cl350 w/oem kehin carbs).

    Nice rebuild and DIY!

  29. Nice blog posting, i will practice it by myself to clean my carburetor

  30. I have been looking all over the internet and this this the most helpful post I have found on how to rebuild a SB350 carb. Thanks for taking the time to do this.

  31. Hi, you really posted a nice blog, it has lots of information.
    Thanks for sharing this....
    4 Post Hoists

  32. I've been looking into this whole pilot jet problem that I have been having. Both of them have the rubber stopper in them but what about the piece that is pressed in behind the stopper. Do I leave that in when I do a chem-dip? Or do I remove it? If so, how do I remove it?

  33. Hi, you have did really well this is awesome post.
    This is full of information and lots of technical knoledge.
    Workshop Garage

  34. Hello thanks for sharing this nice post.
    It is really awesome because the way of writing and the information you have shared.
    Thanks once again.
    Workshop Equipment

  35. Wish the author would answer these questions, these are great questions here, like why is the kit gasket round? Pls help

  36. Great write up - thank you!