SOHC.co.uk Forums > CB350/400

400F carb balancing

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dbscots:
I hope there is someone out there who is good with carbs. because I'm having a problem that's driving me crazy.  I'm cleaning up a 1976 CB400F for my daughter. At this point everything's done. The carburetors were cleaned and rebuilt. I'm trying to balance them with a vacuum balancer that uses small balls to measure the amount of vacuum for each carb. Now in order to get the balls to drop into view I need to decrease the vacuum by turning the adjustment screw counterclockwise. Doing this raises the slide which in turn raises the idle. I was able to get all four balls dead even straight across. The only problem was that the bike was idling at about 4200rpm. So I turned the adjustment screws clockwise which increases the vacuum and lowers the slides. The idle comes down but the increased vacuum draws the balls upward and out of site in their tubes. No amount of fiddling on my part has been able to change this. Does anyone have any ideas that I can use to correct this problem?
Thanks in advance,
dbscots

Bitsa (Ralph Wright - RIP):
Hi dbscots.When you managed to get all the balls level did you try turning the throttle stop screw out to decrease the tickover?If doing this does nothing to slow it down then you have to screw the stop in to slightly increase tickover then lower the slides.I have done many 400/4s and all the ones I did as you pinch up the locknut you will find the vacuums alter slightly so you have to compensate with the screws.I hope this is clear to you they are fiddly 750s are much easier.Also while doing this I recommend a fan in front of the motor as it will get ruddy hot quick.I assume you have set the tappets and timing first.
Cheers
Bitsa

steven400/4:
i had the same problem with mine and it ended up being the chock flaps some of them was not open fully where are you??

dbscots:
Thanks for your advice guys. I plan on looking into all of your suggestions as soon as possible. but when I went out today to go over the checklist I wrote up I found that the right side coil had quit on me. The carbs will have to wait until I get that replaced.
I'll keep you posted.
dbscots

ST1100:
How are the experiences with Carbtune gauges on SOHC's?
http://www.carbtune.co.uk/index.html

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