Do these floats look buoyant enough to you?

Been trying to isolate the issue with all 4 carbs' fuel overflow on my wifes CB350four I've been building. I recently rebuilt them, but the kit did not include new floats.

I know that the float needles and seats are seated and sealed, not leaking, and I can blow into the fuel line and they will stay seated. I've also confirmed that the overflow tubes do not have any cracks/leaks in them as well.

So I thought I'd test the buoyancy of the floats in some fuel. I want to say they should be floating a little higher, but I don't really know for sure. Can any of you tell by looking at these?

https://www.youtube.com/watch?v=Ylq90X1mvdI&feature=youtu.be

I would guess that if they do not leak then they would have the proper buoyancy, what are they made of, looks like plastic in the pics. I would like to add however that I think they make your ass look big.

The floats look fine. If you saved the factory brass when you rebuilt the carbs, take out the "kit" brass and clean and replace the OEM parts. Put the factory needle and seat assemblies back in, but first take a q-tip with some metal polish on it and spin it (by hand) on the seat to polish it up. You also want to polish the bore that the needle shaft slides into. I have seen this bore be rough enough from fuel deposits to hang the needle despite the needle being very obviously plenty loose in the bore. Do that to the kit seats if you threw out the factory parts, or if there is a noticeable groove in the old needle. (Unlikely unless corrosion is involved as the steel needles are very hard compared to the brass seat). Make sure that the tensioning pin in the needle is working perfectly freely and is properly spring loaded. If they are sticky a bit of massaging with some carb cleaner usually restores them. Generally I would use the OEM parts even if I had to clean the tensioning pins. You can spin the needle's point in the q-tip as well. Examine the brass bridge that connects the floats. Where the needle contacts the adjustment tab, there must be absolutely no wear. I see very obvious markings in your video. If there is any marking, you must sand it absolutely smooth (and it MUST be FLAT) with #600 grit minimum and polish so there is no mark what so ever. That surface must be perfectly flat and smooth. If you have to file it flat do so, and then sand and polish. I actually (what are the chances!) happen to have a set of these carbs (actually from a 400 four I'm pretty sure) sitting here in front of me, and the adjustment tab makes a fairly severe angle with the needle when the floats are properly adjusted so this area is especially important presuming yours are the same. This angle puts a side load on the needle which will rob some of the float pressure and thus the assembly will be more prone to leaking. Ideally, this surface will be perpendicular to the needle when the floats are at the correct height. Also check the pins that the floats pivot on - they can not be bent or scratched and the float must swing absolutely freely. The pin should fall easily through the brass bridge no matter where it is rotated in the bore. And it should slide easily through its mount in the main casting. Check both parts separately without assembling the float into the main casting. With the carb bodies upside down and the fuel bowl sealing surface level, the bottom of the floats should also be level (that's the actual bottom of the floats, like when the when the carbs are right side up.). In other words, the bottom of the floats should be parallel with the gasket surface when gravity is working to close the needle and seat assembly. Make sure the adjustment tab is bent correctly and has no twist - it must be perfectly parallel to the rest of the bridge when viewed from the front (engine side).

The needle and seat/float assembly is simple and reliable, but because the forces to make it work are so very small, it doesn't take much to cause trouble. Any sort of scratch or tiny misalignment can cause it to hang up. For example, the assembled length of the needle and seat, including the thickness of the washer under the seat is critical to be the exact correct length, otherwise the float assembly will be either too high or too low, and compensating with the adjusting tab to get the float height right may make the tab's orientation to the needle to be incorrect and cause the mechanism to work improperly. That is one reason I always keep the OEM parts. If you have to swap them for inferior aftermarket part, it's time to get a micrometer out to see if they are precisely the same.

jpmobius: Thank you for sharing so much info. After considering everything you wrote, I've started re-aligning the tabs on the floats. And after digging into it I discovered something...

While I didn't keep ALL parts from the original brass, I did still have a few float needles. They were a mix of different ones, but an a couple of them I noticed that they were slightly different than the ones in my rebuild kits.

The new float needles' pins are 1mm shorter, and the neck just before the needle end is slightly shorter as well. This in itself makes it a pretty obvious red flag as to why the fuel was overflowing. This week, for the sake of being extra thorough, I went ahead and ordered new float pivot pins even thought the floats still moved freely. I haven't put everything back together yet, since I'll still have those new pins to install once they've arrived.

But I'm wondering, since the float needles are roughly 1-1.5mm shorter than the old ones; could I simply add that difference to the float level height? Since the floats are supposed to be 21.5mm, should I change it to 22.5-23mm? Thats what I'm going to attempt and see what happens.

The float height needs to be the same regardless of the mechanical bits that operate the valve. The only time you would want to change the float height would be if you intend a tuning change.

Keep in mind that the operating length of the needle valve assembly is the TOTAL length which would include the gasket under the seat brass. That length will cause the pin that the float arm adjustment tang touches to be in the right or wrong place. So, if your new needles are shorter (or longer) than the originals, hopefully the difference is made up by the depth of the bore for the seat and/or the thickness of the gasket. Obviously, if you use needles that differ from the originals and use the old seats the overall length will be different and won't work as original. You may be able to adjust the tang on the float arm to compensate, but this will only work for small discrepancies. The limit is the angle between the stroke of the needle and the tang. That angle needs to be pretty close to 900 when the float height is set correctly. That way, the tang pushes directly up on the needle when the bowl is filled to the correct height and the inflow of fuel needs to be stopped. As the angle moves away from 900 either way, part of the effort on the needle is sideways, which pushes the needle partly into the side of the bore reducing how much pressure there is on the actual seat. If this is great enough of an angle, the seat pressure will be reduced enough to let fuel in even with the floats at the top of the bowl.

This may seem a bit complicated, but at the end it is fairly simple. The simplest thing to do is get authentic Keihn needle and seat assemblies for your carbs because it is difficult to know if you have a mismatch of parts. Don't forget the gasket. That should enable you to get a proper angle on the adjustment tang.

Alternatively, you can adjust the tang on its own so that it is horizontal when the float is at the correct height. In your case, it would need to be parallel with the bottom of the float because this is how the float is oriented when at the correct height with the bowl full of fuel. Then you adjust the float height when assembled into the carb by adjusting the height of the needle and seat assembly by changing the thickness of the seat brass gasket. A thicker gasket will effectively make the assembly longer and vice versa.

I would bet that obtaining the correct factory seat assemblies, polishing them as described (yes, this is a good idea even on new seats), and then adjusting the repaired (flattened and polished) tangs to achieve the correct float height will cure your troubles. Having to fuss with the gasket thickness to get everything right is rare in my experience.

That actually makes a lot of sense. There were a couple of things you mentioned that I hadn't considered before, and now that you have it's explained a few things about how they're supposed to work. Still waiting on the new float pivot pins to arrive. When they do I'll make some more adjustments where needed and report back.