Topic: CB400F Float Bowl Gaskets Leaking

[OCW85]

When I bought my CB400F it ran rough and it was pretty obvious the carbs needed cleaning. That said, I took the carbs apart and cleaned everything real well. I replaced the main jets and the gaskets and put everything back together.

After getting the carbs back on (which is a real PITA as I'm sure you know), I turned the gas back on and BAM, gas starts pouring out from all four bowls around seal/gaskets at a very fast rate there was no gas draining from the overflow tubes). At first I thought it was the actual floats, which I had to adjust, but given the overflow drain sits a little higher than the seals, I'm thinking it may be the replacement gaskets, which I got from 4 into 1 (I could be totally wrong). When I put the bowls back on I noticed they came a mm or 2 from touching the carbs, but eventually they came together when I screwed everything down - is that normal?

That being said, I couldn't resist filling the bowls with gas, turning off the gas, and giving her a test. After a few kicks, she fired right up and sounded MUCH better than before. Now if I can only figure out this gas issue that would be great.

Any feedback/suggestions would be greatly appreciated!

THANKS

[Tews19]

Look up clear tube method. That will help you set the height of the floats

[OCW85]

Thanks Tews - do you think it's the floats vs. the gaskets?

[Gene]

Yes.  The gaskets, if everything else is working well, shouldn't really see any fuel on them.

[OCW85]

Here's a video of what's going on...

Not sure if the upload worked.

[Tews19]

I can't download or view your video. I honestly haven't gone through 400 carbs. I do know that if the floats were ever messed with that may be a culprti. As may a cracked tube in the bowl. But I am not sure if the 400s come with that type of bowl.

[Restoration Fan]

Since it appears to be leaking from many (if not all) of the bowls, I would start with the float height adjustment.  Once you confirm all of those are correct, if it still leaks, then I'd look at new gaskets.  But I wouldn't replace them until I was sure the issue isn't that your floats are set wrong.

[Gene]

First - check that your overflow tubes are not clogged - even if your floats are not right fuel should not be leaking out of the seam like that.

Any fuel spilling should be pouring out of the overflow tubes.  OR - and I don't know 400 carbs - the fuel line (connector) between the carbs is leaking.  Are you missing O-rings there?

[JetgreenK1]

If they are anything like 500 carbs, it is the darn floats acting up. Adjustment there may solve the issue.

[OCW85]

I checked the float height, again, and everything looks good at 21mm. They should just barely touch the spring-loaded pin, correct?

Did not check the overflow tubes, but even if they are not clogged, there is still an issue with too much gas getting in the bowl. I doubled checked the gaskets and put everything back together. I hooked up the gas to the carbs (but didn't bother doing a full install) and they still leak and it looks like the issue is the gaskets. I screwed everything down real tight and I don't want to strip or break anything by going too crazy with  the screwdriver.

I do have to say, when I originally installed the carb gaskets, I had to stretch them a little bit to get them to fit in the gasket groove - could that be the issue? They were a hair smaller than the gasket groove and there was no way to get them to stay in place besides stretching them out a bit. Rookie movie now that I think about it - that may be the issue....

With regards to the float, I'm 99% positive they installed correctly with the rounded end facing up (when installed).

[Gene]

NOT. THE. GASKETS. The gaskets should never see fuel if everything is right.

Check again.  Do everything. Nothing personal, just do it again.

[OCW85]

Gene, I have checked everythinf and gas still leaks from the gaskets. From my other searches, this is not an "unheard of" problem. That said, maybe it's the valve inside the bowl and/or the o-ring around the assembly. I'm confident the float height is correct and the floats themselves are not sticking.

[carnivorous chicken]

NOT. THE. GASKETS. The gaskets should never see fuel if everything is right.

Check again.  Do everything. Nothing personal, just do it again.

This, again. Replacing your O-rings (not gaskets) won't solve this problem. This is what's going on: incorrect float height (but you seem to have ruled that out -- but are you sure?), stuck float valve, or floats not working properly. Furthermore, you should check to make sure your overflow tubes aren't all clogged up because as someone already pointed out, this is where the gas should be overflowing. 

[marting100]

Hi There! it's hard to tell from where the gas is leaking in your video, not sure it's the gaskets. I would make sure the main fuel tubing on top of carbs is not leaking. Did you use the round or pre shaped bowl gaskets? When I did mine, I have used viton gaskets on everything except for the bowl I have used the pre shaped ones from 4into1, they are easier to install. Never got any leaks.
Good luck!
M

[OCW85]

Hi M,

I wish I could get a better shot of the leak. That said, the gaskets are from 4into1 and they are reshaped, not round. That said, when I got them, I had to stretch them a little to get them to remotely stay in place (before someone suggested using grease). I am going back to the drawing board, but I will take an even closer look at everything this time around. Thanks!

[marting100]

Hi! one thing that came to my mind is the attention at cleaning the gasket groove very well, same for the other parts where the gaskets get in contact. I am just a little concern about the stretching, If I remember well, I did not have to stretch mine, well maybe a little. If you put some grease to make them hold while you install, it's still possible that they go out of place if you are not very very care full when you screw the bowls in place. I have seen peoples put a little bit of super glue in the bowl grooves to make sure they dont come out while installing (I did not do that on mine). Good luck!
M