Carb Adjustment help '72 CB350K4

Hello all,

I am having problems getting my carbs adjusted properly and was hoping there was an expert on here that might be able to help me out. I have a 1972 CB350K4 and I had it running pretty well. It had a little bit of a stumble at constant throttle position so I thought I would rebuild the carbs. I bought a very thorough kit from Common motor collective and set about fully disassembling, cleaning and rebuilding the carbs. While I was in there I got the bright idea that I would set the float height as well so that is potentially a second variable along with the rebuild.

The issue now is that you cannot apply more than half throttle without it bogging completely. It happens no matter what speed you are going (even in neutral). I do find that it revs better with the choke on so it seem like it is either being starved for fuel or is somehow getting an over abundance of air.

This was definitely the result of rebuilding the carb so I am focusing my troubleshooting to the carbs for now. So far I have take the carbs back apart several times to see if I could identify any mistake I might have made but I have yet to find any.

One other observation of note; The air mixture screws seem to produce the highest idle at fully closed. I know that they should be around 1 turn out but I don't know what specifically affects this. I also know that it is only in play at idle but I wanted to add it in case it indicates something else wrong that I can look into.

I set the floats at 23mm using the procedure detailed in this video.


I was careful to use all of the correctly sized jets from the kit (there were 2 different sizes included) and I believe that I used the bigger of the 2 for main jets as that is the size that was in the bike.

I synched the carbs carefully and I had just done the points and timing fairly recently (again, was running pretty well before the rebuild)

I really want to start riding the bike but I just can't seem to get to the bottom of the issue. My next troubleshooting step will probably be to put any of the usable original parts back into the carbs and see if I can't get back to where I was before the rebuild but I hate to go that direction.

One other note; I am running inline fuel filters but they were there before I did the rebuild (come to think of it, they might have been the reason for the slight hesitation at constant throttle) but I really don't think that they are the cause of this issue though.

Any help would be greatly appreciated.

Here is a couple pics of the bike.