Topic: Cb500 carbs leaking badly

[vonvendetta]

So I went for a run the other day and noticed the bike was starting to shift a little rough after 30 minutes on the road, mild slipping. Pulled over and noticed gas just flowing out of the overflow. I've set them to 22mm and replaced the springs to the float bowls. What else should I check for?

[chewbacca5000]

So I went for a run the other day and noticed the bike was starting to shift a little rough after 30 minutes on the road, mild slipping. Pulled over and noticed gas just flowing out of the overflow. I've set them to 22mm and replaced the springs to the float bowls. What else should I check for?

What do you mean springs to the float bowls?

[vonvendetta]

I'm sorry, the little pin spring thing the float bowl closes when it fills with gas.

Float needle!

[calj737]

Any chance you installed your floats upside down?

[vonvendetta]

Any chance you installed your floats upside down?

There could be a chance, I'd feel quite stupid if I did! I'll pull them tonight to add some pics.

[flybox1]

out of one carb, or all four?

overflow out the overflow tube can only mean:
1. a dysfunction of the float valve(does not seal, bad fit, debris, etc)
2. incorrect fuel height (incorrect float height, float upside down, stuck float, etc)
3. cracked overflow tube (usually shows as a steady drip)
4. poor seal of the bowl drain screw(if your carbs drain screw drains fuel out the overflow)

If your carbs worked fine before, and just started out of nowhere.... id lean towards #1, 2

[chewbacca5000]

Flybox pretty much has it covered.

Debris in the tank is a big one.  Any rust or sediment can keep the float needle from sealing against the seal.  Also, if all 4 are leaking good change the floats are getting hung up.  They can hang easily on the float bowl gasket.  A little dab of super glue will keep them in place.  Make sure floats are clearing the gasket.

Not sure if you took the seats out as part of the cleaning, but on a CB550 it has orings that might not be sealing all the way.

Start with the simple stuff like draining some gas straight from your tank into a clear jar and it should be perfectly clear not no junk.

I would do that before anything else.

[vonvendetta]

I've cleaned and sealed with caswell. All the floats look to be 22mm and are springy.

Have the screwdriver pointing at the one the gas pours out of.

[Bodi]

The list of causes from flybox is where you should look. You replaced the "spring things" that sound like the needle valves... did you replace the entire valve assembly - seat and needle? Where did you get them? There are aftermarket valves, considerably cheaper than KeiHin ones from Honda, and not very good in my experience. I always get OEM ones now, after several problems with the aftermarket ones (about 4X the cost?). There are metal tipped needles and rubber (viton?) tipped ones. The metal ones can be lapped to the orifice if they seep fuel, the rubber ones seal well but once leaky are trash. Dirt in the gas is the #1 cause of dribbling carbs - a bit of crud sticks in a valve which then can"t fully close. Draining the bowl and refilling it can flush the gunk out, a good whack at the carb can dislodge it as well. Rusty tanks produce a lot of rust flakes that catch in the valves. A good tank cleaning, plus ensuring the original filter on the petcock is good, is prescribed: you can add an inline fuel filter after the petcock but some expert techs really dislike them, they can cause fuel flow issues of their own- ymmv.

[vonvendetta]

Took apart and cleaned the hell out of it. Started right up. Now I'm getting valve chatter, just changed valve gaskets...

[vonvendetta]

The list of causes from flybox is where you should look. You replaced the "spring things" that sound like the needle valves... did you replace the entire valve assembly - seat and needle? Where did you get them? There are aftermarket valves, considerably cheaper than KeiHin ones from Honda, and not very good in my experience. I always get OEM ones now, after several problems with the aftermarket ones (about 4X the cost?). There are metal tipped needles and rubber (viton?) tipped ones. The metal ones can be lapped to the orifice if they seep fuel, the rubber ones seal well but once leaky are trash. Dirt in the gas is the #1 cause of dribbling carbs - a bit of crud sticks in a valve which then can"t fully close. Draining the bowl and refilling it can flush the gunk out, a good whack at the carb can dislodge it as well. Rusty tanks produce a lot of rust flakes that catch in the valves. A good tank cleaning, plus ensuring the original filter on the petcock is good, is prescribed: you can add an inline fuel filter after the petcock but some expert techs really dislike them, they can cause fuel flow issues of their own- ymmv.

You are probably 100% correct. I need to invest in better sets. I'm sure it would help diagnose future issues.

[Flyin900]

[quote author=Bodi . The metal ones can be lapped to the orifice if they seep fuel,

Just curious how you would lap a metal fuel valve to the brass seat? What would you use the hold the fuel valve properly and vertical to the seat and what would you use as the cutting/abrasive compound.

Often thought about this as an option yet never figured how to hold that tiny fuel valve and align it in the bore of the seat.

[Bodi]

Lapping - I put a dab of Solvol on the tip and turn it in the seat a bit with a small rubber tube that grips the round part above the flutes. I guess the flutes are tight enough in the seat bore that the needle is held square to the seat? It works, anyway. You can inspect the needle tip with a loupe and see if it's damaged beyond redemption. Just a touch of lapping should show a bright band around the needle, that should do it.

[Flyin900]

Thanks Bodi...

I have had some issues with minor seeping from two of my carbs and wondered if you could lap rather than spend a fortune on Honda parts, or take a chance with the aftermarket kits.

Cheers