Topic: Odd Carb gas leak 77' CB550k

[DarkLinkX5]

For whatever reason gas is getting sucked up the emulsion tube and out the air filters.
its NOT going out the overflow tubes, so i doubt its a float issue. I've properly set and checked them for movement and seal.
I've rebuilt them to factory spec. jet size, float height, etc, and synced them. whatever i do this issue persists and not only waste gas but causes multiple running issues.
if not for this issue I'd be on the road.
Any help is much appreciated.
this is a 1977 CB550k

The picture (not my carbs but the same) shows where the gas flows out of with a red circle.

[DarkLinkX5]

this picture shows it flowing out the tube there.  so you know im not crazy.

[DarkLinkX5]

anyone know how to fix it, or do i need to buy another set?
if i could i'd buy some new mikuni carbs but their over $600.... so its ebay gambling or pony up big time.

[Nurse Julie]

That'll be a blockage or a restriction somewhere. If the fuel is coming out of all 4, I would look at cleaning the passages again and re checking / re setting everything again. What level have you set the floats at and what are the A/F mixture screws set at, how many turns out?.

[Maraakate]

I had this problem before on my 77 CB550K and it was a mix of incorrect float height (if you are using aftermarket needles they are junk and the spec given in the book will be wrong!) and the drain tubes in the float bowl were plugged.

[DarkLinkX5]

i did replace my needles. that could be the problem.. i still have the old ones. nothing wrong with them i just replaced everything i could with the new parts.
i think i remember them being slightly different.
should i just put the old needles back in and see? or adjust the new ones up or down?

[Maraakate]

Are the new ones genuine Honda or aftermarket?  If they are aftermarket you will have to do the "clear tube" test to adjust them properly.  Honestly, I know it sucks but just spend the $80 get the real float needles so you don't waste 3-5 days of your life trying to make trash work.  Otherwise, if they are genuine then check the float height again, maybe it's wrong.

Be certain the drain tubes are not plugged.  I originally had a small leak on one carb when I first got the bike running and tried to cheat it with closing off the drain hose with a small bolt.  The leak ended up moving out the plenum.

[DarkLinkX5]

its been awhile since i bought them so i have no idea where i got them from.
are you talking about the float needles or the jet needles?

3/4 drain tubes were actually plugged too. i blew the obstruction out with compressed air.
i had some weird green crap in the bottom of the float bowls. no idea what that was.

[Rosinante]

this picture shows it flowing out the tube there.  so you know im not crazy.

We don't know that. 

[Maraakate]

its been awhile since i bought them so i have no idea where i got them from.
are you talking about the float needles or the jet needles?

3/4 drain tubes were actually plugged too. i blew the obstruction out with compressed air.
i had some weird green crap in the bottom of the float bowls. no idea what that was.

Float needles, but if you used any aftermarket brass (jets and needles, o-rings probably OK) remove it immediately unless you want to have a lot of "fun" trying to retune.

[DarkLinkX5]

i'm giving up on these carbs. the more i take them apart the worse the problem gets.
almost half of the float bowl threads are stripped out because the aluminum is so damn soft. im now getting leaks from the bowl oring seals.
im not wrenching on them with the screwdriver either i stop when the screw stops. and sometimes the screw just dont stop turning.

idk if i want another ebay carb gamble.. these ones have been crap since i got them. all im doing is trying to polish a turd that keeps falling apart.
I'll go with brand new mikuni carbs if i can fine one that would fit.

[Maraakate]

It sounds like you are ham-handing it.  Doesn't matter what modern carbs you may have on something else; these older carbs don't take kindly to ham-handing repairs.  Just tighten the float bowl screws until they're snug, then maybe 1/8-1/4 turn.  Don't need to get nuts.  Same with the all the brass.

You can still get new screws for the float bowls, direct from Honda.  They are slightly longer than the originals but will fit, this should give you enough "bite" to get them on properly.

If you get new Mikuni carbs, then you will be putting pods on if you don't make a proper adapter to the airbox, which these bikes don't enjoy unless you have plans to race it or ride it in very specific conditions.  You'll end up becoming a guinea pig where you will be buying lots of carefully selected jets and doing lots of plug chops.  Maybe you have the patience for this, maybe it is fun for you.  But I think for most people it's not.

Anyways, call your local Honda dealer or go to Partzilla and order 93892-04016-08, this is the screw for the float bowls.  If you're talking about a botched drain screw 4into1.com has new ones.

Don't give up.  You're so close.  When I first got my bike I chased the carbs pissing for two weeks.  Now I've been riding it all the time for the past year.  Some additional advice though, if you have not replaced the o-rings on the fuel connecting tubes between the carbs do it now.  When I fixed the float height with the OEM needles then it started pissing out of the fuel connecting tubes.  If you fix one leak it's going to find the next weak point.  So just do all the o-rings now.  Those o-rings for the connecting tubes aren't super special, you should be able to find something from one of those "fuel injector" assorted o-ring kits they sell at the autozone.  You can replace these tubes without having to entirely separate the carbs (I highly recommend you don't separate them as it can be difficult to get them back together again if you're not well organized and didn't document the process).  I believe when I did it I was able to loosen part of the linkage enough to be able to do both tubes.  Just be mindful of any springs and their orientation.  Go slow.  Don't be mad.  If you get mad, take a break.

[DarkLinkX5]

it might sound like im being heavy handed but i am being careful with these screws. i let some bozo look at them a while back to fix this leaking issue and only needed up wasting money and having more screw holes striped out. i originally had 2-3 that were a bit loose but held on the threads before i handed them off.  he drilled and taped 2 of the holes for a bigger screw without consulting first, and he also did a half ass job at soldering a crack in an overflow tube. he worked on motorcycles and motorsports for a living before he retired and started doing it from home.
i dont want anymore hands on these. I'll probably end up with every hole drilled and tapped in random screw sizes, and maybe even a few zip ties, and duct tape if i let someone else do it..

i have a pack of assorted lengths of these screws. they're just standard M4 Philips Pan head.

im just mostly frustrated because of my lack of sleep and amount of time spent on this one issue. I'll continue.. really dont want to spend $700 on new carbs.

i replaced all the o-rings in it including those. when i dissemble the carbs i lay everything out in a organized way so everything goes back where it came from. like an exploded view.
im meticulous and methodical.
i do anything from CAD, CNC, electrical, circuit board design, surface mount soldering components smaller than half a grain of rice, and other careful and attentive work. i picked up this bike because i was interested in working on one since childhood, and i like mechanical work and fixing things in general. i really want to restore it to its former glory.

[DarkLinkX5]

well i did what i could and its not leaking from that spot but i am getting a leak around the far right side float bowl seal.
i might just replace those gaskets again they stretched out and it might be pinching and letting gas out or it flattened. 

thank you for the help

[Maraakate]

I had problems with the float gaskets, if you're using ones from a "rebuild kit" from ebay they're basically only good for one maybe two uses.

4into1 sells a set for $10: https://4into1.com/shaped-o-ring-float-bowl-gasket-set-of-4-honda-cb550-650-750/ these ones are OK.  I believe K&L has one too, but you can still get the official ones, they're just expensive at about $15-$20/kit.  Does the bowl leak when on the centerstand with the gas on?  If yes, the leak maybe from incorrect float height on one of the carbs.  I believe (but someone else needs to chime in) that you can test without the gaskets to verify if it's the bowl gasket keeping the float stuck.  But only on a centerstand in a non-running state.

[DarkLinkX5]

i got them from 4into1.
it didn't leak until i ran the bike for a minute. i did try opening some drain screws for a second and see if any leak out the overflow and that seemed fine.
i left the fuel on and went inside for my keys and everything was still dry, but the far right carb just started leaking around the gasket seal after i turned the engine off.
the screws were snug so the gasket being worn from repeated use is my only lead. i did buy and install them first in 2018 so they could just be drying out too.
I'll have to try new ones for sure.