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Discussion Starter · #1 ·
Any CM/CB400 owners know how to sync their carbs? I know the process but I'm not having any luck getting tools into this area to do any work. Have no idea why the Honda engineers designed it that way. Very frustrating. Pretty bad when its way easier to sync my four cylinder Kawi than this little twin :twisted:

If anyone has successfully done this, what type of tools/methods did you use?

I just got back from a nice run on the bike, and the only real issue is some vibration that I'm thinking is due to the carbs being out of sync. Hoping this will help.

Any tips would be greatly appreciated.
 

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Discussion Starter · #3 ·
Should have made my first post a bit clearer, must have been the anger taking over when I wrote it :evil: The taps already exist in the head for the vacuum gauges, they're stock on the 400's, but the problem is accessing the adjusting screw and lock nut. Its buried deep between the carbs and is impossible to reach. I think my only choice is to remove the carbs, loosen the lock nut, put the carbs back on, adjust the synchronizing screw, then take the carbs back off to tighten the nut. I really can't believe they made it like this.
 

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I assume you have the tank removed already and either connected via long fuel hose or have an alternative fuel source. As for getting to the locknut and adjustment screw I used an 8mm socket on an 18 inch flex shaft to loosen the locknut just barely. After that I used an 18 inch flathead screw driver to sync the carbs. Retighten the locknut and recheck the sync. I found that I had to turn the adjustment screw slightly counter clockwise to compensate for tightening the locknut. Your results may vary.
 

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Discussion Starter · #5 ·
Thanks Mike. I tried it first with the tank on, and then with it off, still couldn't get any tool in there. I think the problem is that I don't have the correct tools for this job. I may see if I can get out over lunch tomorrow to pick up a flex shaft like you mentioned.

To help things out though, tonight I removed the carbs so I could loosen the lock nut. So tomorrow I'll hopefully get time to sync them. If I can't get the lock nut tightened still, I'll just remove the carbs yet again and tighten it.

Glad I removed the carbs now, the spring that connects the left and right side choke plates wasn't on correctly. It must have caught on something the last time I installed the carbs and so the right side choke plate wasn't even functioning. I'm hoping this is the cause of my hard starting issue. Too late to try it so I'll start it tomorrow after work to see if it helps.
 

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Don't the 360's have a hole in the frame roughly where it splits just below the tail of the tank? That's where the sync screw is accessed using a long screwdriver and some suitable socket for the locknut.


NE

Well duh. For some reason I thought I read CB360.... More coffee needed.
 

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I did mine with an 8mm box end wrench and a standard flat head screwdriver. All you have to do is remove the tank.

with the bike off, turn the throttle to 100% open, you can now access the lock nut with the open end of the 8mm wrench.

from there, let the throttle return to closed and adjust the synch with a small flat head screwdriver that's at east 8" long.

done deal, hope this helps!
 
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