Topic: Carb leaking after rebuild - 1973 CB350F

[Lou]

Hi all, I finished rebuilding my 4 carbs and one of the carbs is leaking gas. I saw it when I opened the petcock to let gas in ... gas flowed through the inline filter nicely and then moments later gas started dripping from the bottom of one if the carbs. Looks like it's coming from the area where the bowl attaches to the carb -OR- maybe from the overflow tube that comes out of the bottom of the bowl. Seems more like from the spot where the bowl attaches.

The carbs had been professionally rebuilt before I rebuilt them. So they're clean and in good shape. Had a bad gas tank which I suspect made the bike stop running - died and wouldn't re-start. Got a clean replacement tank off of Ebay.

I used a rebuild kit from 4into1.com. Found a detailed step by step video online and followed the instructions to a tee, and took my time. All new jets, etc.

Any ideas on how to remedy? Remove the bowl and replace the gasket? Remove the bowl and see if the float is stuck?

Any tips or suggestions would be greatly appreciated. Thanks!

[carnivorous chicken]

If it's leaking jsut sitting there, it's not the gasket's fault. The fuel level in the bowl should be below the gasket (unless the bike is leaning).

A few things to check:
-- are there cracks in the overflow tube?
-- is the float height set correctly?
-- is there an issue with the float valve? something caught in it, or it doesn't shut off fuel flow completely?
-- is there something impeding the float from shutting off the valve?
For the latter, sometimes a light rap with a hammer will free a stuck float, although that's not a long-term fix, and when the fuel level gets below the point where it will stick, it'll just stick again. It's also possible that a small groove has been worn into the tang on your float which makes it hard to close completely.

[ADW]

If it's leaking jsut sitting there, it's not the gasket's fault. The fuel level in the bowl should be below the gasket (unless the bike is leaning).

A few things to check:
-- are there cracks in the overflow tube?
-- is the float height set correctly?
-- is there an issue with the float valve? something caught in it, or it doesn't shut off fuel flow completely?
-- is there something impeding the float from shutting off the valve?
For the latter, sometimes a light rap with a hammer will free a stuck float, although that's not a long-term fix, and when the fuel level gets below the point where it will stick, it'll just stick again. It's also possible that a small groove has been worn into the tang on your float which makes it hard to close completely.

Often a dry carb will stick on initial usage. Happens to my multi-carb bikes after the carbs have been drained for the winter; in the spring one will stick and leak, but it'll fix itself after a bit. I'd say give 'er a few taps with a screwdriver handle and try again. It may free itself.

[Lou]

Thanks for the replies. I appreciate the tips.

I'm going to pull the carbs off this weekend and open the bowl of the carb that leaks. I'm thinking it has something to do with the float.

[camshaft1991]

The float height can be iffy. OEM is 21mm but depending on the quality of the float switch you get (less stiff or more) you might have to adjust +/-3mm. Also if you’re using original floats/ old floats.

If it is a stuck float switch (float switch is snagged and is stuck open) then nothing is stopping the fuel from entering the carb.
Using the bunt end of a tool like a screw driver will work, but I’d recommend using a small block of wood like a chisel and tap each of the carbs gently a few times with a hammer (small hammer on the safe side). The bunt end of a screw driver can leave slight superficial divots, if you look close. Use or make something that resembles a 2x4.. (similar in ratio) a block that has enough surface area for good hammer contact and to distribute the force of the hammer blows while at same time able to reach the inner carbs. The best spot to lodge the little block is right under the rigid lip of the carb bowl that mates with the carb housing. You should probably tap your carbs every time you fill them from empty. Open up your petcock halfway and start with your known leaky carb. Also make sure those “spouts” , the brass overflow tubes, have tubing connected to them at the bottom. Have the tubes run down the backside of the crankcase and have them hang a little bit below the engine. Gas on the engine has a good chance of setting on fire. I literally danced around that fire a few times no pub intended. I use windshield wiper tubing and mini zip ties. It’s not long lasting but I don’t mind replacing them annually.


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[fohunnertfo]

This has happened to me after cleaning or rebuilding the carbs on my 2 400F's and 350F. Out of 5 efforts, I have had the floats stick 3 times and run out the overflow tubes.  Problem was solved by taking the bike on a quick ride, less than a mile.  Rough road is better, I guess, but the smooth paved roads around my house worked fine.  The vibration and road bumps fixed whatever float sticking issues were occurring.  The overflow problem did not reoccur.  Pretty simple and fun fix, maybe first thing to try??dyxbeb

[ADW]

This has happened to me after cleaning or rebuilding the carbs on my 2 400F's and 350F. Out of 5 efforts, I have had the floats stick 3 times and run out the overflow tubes.  Problem was solved by taking the bike on a quick ride, less than a mile.  Rough road is better, I guess, but the smooth paved roads around my house worked fine.  The vibration and road bumps fixed whatever float sticking issues were occurring.  The overflow problem did not reoccur.  Pretty simple and fun fix, maybe first thing to try??dyxbeb

Exactly my point posted earlier...it seems they just gotta "wiggle around a bit" and likely will fix themselves. Mine do the same thing.

[Lou]

Took them apart this weekend. It was a stuck float. The pin holding the float in place had a sight bend in it so it wasn't allowing the float to move easily. Replaced that float and pin. Put it back together and all good now.

One of the other carbs started draining from the drain tube. Some taps on the bowl stopped that. Carbs are good now. Thanks again for the advice!