Topic: Carb Questiion - CB400F

[grumpy56]

First of many......Does gas flow through this hose to feed the outside carb? This one of mine seems to be leaking. Need to remove carbs from manifold to fix this? Thanks.

[MoMo]

seems to me that your floats are stuck and gas is overflowing out of those tubes.  Carb removal is a pita on the 400.  Good luck with the bike, Larry

[Gibbon]

Hello grumpy.

If your 400 is anything like my 350 that tube between the outer carbs is the float chamber vent.
The fuel feed is a brass tube with O ring seals. In your picture the fuel feed pipe is to the right of the black tube underneath the choke shaft.

Removing the carbs is difficult. I have unfastened the air-box and wiggled it toward the back of the bike to gain a bit more clearance for the carb's.

[Deltarider]

First check all four vent.

[Flyin900]

First of many......Does gas flow through this hose to feed the outside carb? This one of mine seems to be leaking. Need to remove carbs from manifold to fix this? Thanks.

Those are interconnected vents to equalize the inside float bowl atmospheric pressure. The fuel feeds are where your brass T is located on the lower area of the carb bodies from your fuel line connection. You will likely need to remove the carbs to correct any leaks. The floats maybe sticking and some light taps on the offending float bowls with a screwdriver plastic handle will sometimes fix the issue.

You can download the FSM off this site for free if you don’t have a service manual for the bike.

[Deltarider]

No need to pull the rack yet. First comes the diagnosis. It's easy enough to check if all 4 carbs vent and it's easy enough to check all floats operate as they should. When the vents are all OK, but there's a float that doesn't work as it should, first step is tapping on and/or flushing that particular bowl. If then - after tapping and/or flushing - that float still does not work as it should, it will be necessary to open that bowl for further inspection. When that particular bowl is either #1 or #4, you may be able to do it with the rack in situ. When all is OK again, I recommend to add some fuel system cleaner at the first few tankstops.
Has your bike been inactive for a long period of time?

[grumpy56]

Yes bike has been sitting for many years. I will need to take them all apart and rebuild I'm sure. Perhaps as suggested I should just rebuild what I can with them in the rack and then connect a gas line to them to see if I have any leaks prior to putting them back on the bike. Note that I already have the carbs off the bike.

[Tracksnblades1]

Like delta said….+ an unfixed leak will continue to leak even after you fix your float controlled fuel levels...😩

[newday777]

Yes bike has been sitting for many years. I will need to take them all apart and rebuild I'm sure. Perhaps as suggested I should just rebuild what I can with them in the rack and then connect a gas line to them to see if I have any leaks prior to putting them back on the bike. Note that I already have the carbs off the bike.

Do not use brass from aftermarket rebuild kits. Clean the original brass parts.
If it sat from the 80s and 90s, hopefully it isn't corroded from the garbage they put in gas at the pumps here in the states.

[Deltarider]

After such a long period of sitting, O-rings may have shrunk and as a consequence will leak. Usually after a wile of being in contact with fuel again, they can swell back to their original size and seal again. I have seen this happen more than once, especially those around the T-joints, where the fuel is distributed. It saves you separating the carbs from the rack.
All in all it may well be, you got to have the rack on the table. I just read you have it already there.
This would be my working order. Open floatbowls and remove the jets, tubes, etc for inspection. Have 4 bowls ready 'cause you want to keep parts of each carb separated. Clean and refit.
The little O-rings around the main jets may need to be renewed. You can pull the needle jets, once you have removed the main jets. This is best done by bringing the slides in full throttle position and insert a wooden pick from below, cant it and usually you can wiggle the tubes out. Anyway, I always managed without having to open the carb top lids. WD-40 or similar stuff may help. Slow jets in particular need to be cleaned and now you're at it, you may as well spray some carbcleaner in all four orifices of each slow circuit. Apart from the slow jet itself, these orifices normally stay clean, but now you're at it, it won't harm checking the passages are clear. When you remove the airscrews from the sides, first make notes of how many turns out they're set now. You do this by counting the turns when you screw them in completely, but gently! Realise they may have been set in various positions by Honda or dealer. So make notes.
Carefully remove the floats, floatpins and floatneedles and inspect them using a magnifying glass. Especially the floatpins, the tip of the floatneedles and the corresponding valve seats probably will need cleaning and some light polishing without using abbrasive stuff however.
Do NOT 'adjust' the floattangs unless you are 100% convinced they have been messed with by a PO.
Normally they don't need readjusting ever.
All the brassware can be reused. I'd abstain from ultrasonic cleaning. May work for other carbs. Yours don't need it.
After refitting the parts and closing the bowls, I would bring the rack in a test position and add fuel through the fuelline(s) and... wait. Even when the supply route leaks somewhere, give it time! As said, it may swell up again to its original size.

[grumpy56]

Thank you all. Good advice. Will let you know of other "challenges" I run into.

P.S. Supposed to receive an electronic ignition from David Silvers today. Was unable to get timing marks to line up with old points or new knock-offs. Hope I am able to with the electronic unit.

[grumpy56]

Still working on Carb #1 and have all components apart except for the needle jet. I am trying to push it out through the body from the main jet side (like a Mikuni), but it does not want to budge. Any thoughts/suggestions?

[robvangulik]

It's a Keihin, try pushing it down TO the mainjet side.

[grumpy56]

Yes, tried that and "presto". However, I screwed up the emulsion tube (please see pic). Any way to repair this or do I need to look for a new carb?

[Alaxy Galaxy]

Yes, tried that and "presto". However, I screwed up the emulsion tube (please see pic). Any way to repair this or do I need to look for a new carb?

You will more than likely need a new carb body. The main jet in fits in there with a grommet. If it's cracked (like yours is) unmetered fuel will be able to slip by on the side and will screw up the F/A mixture.

I'm sorry this happened to you.

I have a few spare bodies if you need one.

[Deltarider]

Oh, I see I forgot something.
For those interested in applying this safe method of checking the fuel levels*, know that the drained quantity of each CB350F/400F bowl should be 46-48 cc.
* The idea to arrive at 'clean' results for comparison, is here: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647 The bonus is that, by draining the bowls, any residue (water, rust, whatever) will be removed.