Topic: 82 CB650 Carbs with a strange leak

[Cozy]

Hey Yall, I'm having a very strange leak from my carbs. The holes marked in the picture are leaking gas, presumably from the float bowls overflowing into there. I just recently refreshed the carbs with new gaskets, jets, float and pins, etc with 4into1's ultimate rebuild kit. I've tried the common fixes, tapping it with a screwdriver to see if the floats seat but no avail. One thing I have noticed is that if I take any of the individual float needles and press them shut, it'll stop ALL of the carbs from leaking from that hole.

Any simple issues I should check before I just say screw it and have them rebuilt by a shop?

[fizzlebottom]

If you have the original floats and they aren't cracked, reinstall them. I have these exact same carbs and have had a few floats from 4-into-1 last only a season or not at all. The Keihin floats aren't adjustable, but mine are 40 years old now and still in spec. After this, just make sure the rubber needles aren't damaged and that the brass seats are clean and not corroded at all.

Second, it doesn't look like you have the T-joints installed. Are those just missing or do you have the ports blocked off? Don't block them off by any means. You should replace the joints if needed. Randakk's sells them for the CBX and they're directly compatible with the 81-82 CB650 carbs.

[Scott S]

 I don't see how gas from over full float bowls could migrate up there without coming out of the throats.

[Cozy]

If you have the original floats and they aren't cracked, reinstall them. I have these exact same carbs and have had a few floats from 4-into-1 last only a season or not at all. The Keihin floats aren't adjustable, but mine are 40 years old now and still in spec. After this, just make sure the rubber needles aren't damaged and that the brass seats are clean and not corroded at all.

Second, it doesn't look like you have the T-joints installed. Are those just missing or do you have the ports blocked off? Don't block them off by any means. You should replace the joints if needed. Randakk's sells them for the CBX and they're directly compatible with the 81-82 CB650 carbs.

I have 1-2 and 3-4 just directly connected with a hose line. Should I tee it off to atmosphere instead?

I do not have the originals unfortunately. If I can find a set off of ebay that're oem I may just go that route if the 4into1 units are not the greatest.

THe seats are in good condition but could use a good polish which I will get to soon, hopefully that helps.

[Cozy]

I don't see how gas from over full float bowls could migrate up there without coming out of the throats.

Thats what is perplexing me so much. It isn't leaking anywhere besides out of that piece. To be frank I dont even know what it is.

[fizzlebottom]

Huh. Yeah this is a weird one, especially since I don't think fuel really goes up that high in the bodies. And because you're showing them from the intake side, meaning those butterflies are the choke plates you're showing.

Wondering if you have some really funky blockage somewhere, or if you reassembled things in the piston chambers wrong? man this is a doozy. Is fuel making its way into the piston chambers?

[RAFster122s]

Did you change out the air cutoff valves? I presume you sprayed carb cleaner through all the tiny passageways to ensure flow was good through them. The CV carbs if like on my CX500 have lots of tiny air passageways. Hopefully you did not use aftermarket brass in the carbs. Most aftermarket brass is sized wrong.

I believe these are air bleed passageways that lead to thepisons in the domes.
Fuel usually does not come out these...

[fizzlebottom]

Did you change out the air cutoff valves?

No air cut off valves on these carbs.

Something I just thought about is the vacuum petcock. Most folks end up removing that thing for 2 reasons:

1. So far as I can tell, it was put there to as a bandaid to conform to regulations and doesn't honestly do much useful except add more potential failure points.
2 replacement diaphragms are not available anymore. Can't rebuild it properly at all, so once it goes its gone for good.

I truly don't know how it could be possible, but maybe a torn diaphragm is contributing. If it was somehow allowing fuel to make its way into the #2 carb vacuum port and ... sneak into the other carbs too?

Either way, it doesn't hurt to just get that monstrosity off and plug up the #2 vacuum port. Aside from this, open those vacuum piston covers and make sure no fuel is up there. One thing to check is the plastic ring on which each piston sits: They only install properly in one direction. Additionally, make sure you still have the kidney shaped air jet covers installed. Each of them has a rubber/viton gasket + plastic retainer held in by a single screw. If you happened to forget those and fuel is making its way up into the piston chamber, then I suppose it could spill down through the air jets.