Topic: Are your carbs leaking?

[tlbranth]

I think I found a cause that's not been discussed here before. Been having a nasty time trying to get things right. Bench testing my CB750 K0 carbs for fuel level using clear tubing up from drain hole. #3 would overflow. I smoothed out the needles on all 4 carbs with 2000 grit wet&dry silicon carbide then lapped needle to seat using fine valve lapping compound. #3 still overflowed. After many frustrating hours I tried swapping #3 and #4 floats. Then #4 overflowed. I couldn't see anywhere the float was catching except there was a dimple where the needle touched the float. I filed the tab down (quite a bit) to get rid of the indent and do believe the sticking is fixed. Bike still runs like #$%* so the carbs have to come back off for some more loving. But this might be a cause of sticking for some of you.

[ekpent]

Think I have read where Hondaman talks about addressing that indent on the float tab.

[bollingball]

ekpent: yes HondaMan has written about this issue and the fix.           
tlbranth: never hurts to mention it again and you fix it just the way HondaMan said to. Also he or TT wrote about the side of the float hinge can rub against the hinge post and cause the float to hang. check by leaning the carb to both sides and see if it hang while moving the float  and fix by sanding any burrs off. The burrs can be on the post or the float hinge..

[Goldbug]

If your carbs are clean and not leaking now maybe you should try to adjust them on the bike before taking them off again. I mean unless your float height is seriously jacked up, or you need to re-jet I am not sure what pulling the carbs off the bike again is going to accomplish. I guess we need more details about how your bike is running like #$%*.

[ekpent]

One other little tid bit to add to a potential float issue. If you have used any after market float bowl gaskets make sure there is not any of the gasket material protruding into the inside of the bowl area that could potentially cause a rub or interference with the float.

[m in sc]

i just replaced all the needles with viton tipped ones. no leaks at all.

[KRONUS0100]

what model bike did yu get the viton tipped needles from.

[m in sc]

bought em from sudco a few yrs ago for another bike actually. i just had them in the carb parts organiser. all my bikes (9 of various vintages, 8 are carbbed) have been converted to viton tipped. metal to metal seats suck.

[Spanner 1]

ekpent +1 !!....... much more common than known or even considered, your carbs can be pristine clean, float levels exact etc but if the bowl gaskets ( early style carbs ) have expanded any or bowed-in during bowl install, they will contact the side of the float ( already a very small clearance fron the gasket surface) and stop the float rising to close the float valve, or cause the float to hang-up and not close until float pressure at a too high fuel level overrides the interference and 'pops' the float up to close the valve . Either way would  cause carb overflow and/or rich, crappy running 
Try 'pasting' the gaskets to the bowl before install with a smear of Vaseline 

[Goldbug]

How do I find viton needles for CB500/550 carbs?

[m in sc]

partsnmore has em. look up the carb stuff for a 750 k, they are listed for the DOHC models, they will work. 4 bucks each. pretty sure you need to shorter of them(the first one listed). mine are actually mikuni ones for VM28's.. i think.

[fmctm1sw]

I filed the tab down (quite a bit) to get rid of the indent and do believe the sticking is fixed. Bike still runs like #$%* so the carbs have to come back off for some more loving. But this might be a cause of sticking for some of you.

Good observation.  I had a tab that got all scratched up somehow and caused the same thing.

[fmctm1sw]

ekpent: yes HondaMan has written about this issue and the fix. 

Is that in the FAQ or tips and tricks?  I'd be interested in seeing what method he recommends to clean up that tab.  Brute force and ignorance?

[KRONUS0100]

i very carefully applied solder to my float tabs, and then very carefully used a dremel tool to smooth it out.  seems to work well.

[tlbranth]

ekpent +1 !!....... much more common than known or even considered, your carbs can be pristine clean, float levels exact etc but if the bowl gaskets ( early style carbs ) have expanded any or bowed-in during bowl install, they will contact the side of the float ( already a very small clearance fron the gasket surface) and stop the float rising to close the float valve, or cause the float to hang-up and not close until float pressure at a too high fuel level overrides the interference and 'pops' the float up to close the valve . Either way would  cause carb overflow and/or rich, crappy running 
Try 'pasting' the gaskets to the bowl before install with a smear of Vaseline 

Good call Spanner. I'd been eyeballing those gaskets. Didn't look like they'd interfere but it was close enough that if Jupiter and Mars lined up, they'd probably jam the floats. So I trimmed them down on the inside at the sides. Then I carefully daubed some blobs of Permatex Hi Tack in the corners and middles. That should keep them from shifting and allow me to drop the bowls and get them back on  easily without pulling the carbs.
One other tip that I've seen before on this site (Hondaman I think), is to set the idle air screws at ONE turn out. Any less and that bastard will burble and fart all the way to about 1/2 throttle.
Got the thing running pretty well now. Love having the x-ring chain. Nooooooooooo adjustment necessary.