cb550f '76 leaking carbs

[Bert Jan]

So, nr 3 & 4 carb are leaking more than my incontinent grandma. Fuel just leaks out the tubes on the downside of the floatbowl cups. First, it was only the nr3, so i took it apart (on the bike, bowl off, cleaned bowl, float needle and needle-cup.) Put it together and turned on fuel. nr3 dry, nr4 leaking out the tube. WTF?
Took 4 apart, same as above but still leaking mad. Nr3 started again too..

I then bended the little knob on the nr3 floater wich pushes the needle in when bowl gets full. (get it?) Resulting in a non-leaking nr3 carb (obviously) but also no running 3rd cililnder. Took it apart again and bowl 3 was bone-dry. Tell's me the needle thing (floater) works. bended it back, cleaned it.. you know the drill.

3 and 4 are got dripping again. A solid stream of fuel out the overload tubes. As fuel is kinda pricey, i'd like to get it sorted cause i do a solid 1:4 this way.

My knowledge on carbs is ok, but i'm lost here. What's wrong with em? Bike runs fine btw.

 

[VonYinzer]

Set the float height to factory specs. You cant eyeball that. Do it right.

 

[Bert Jan]

Hmm oke i'll do that. Thanks!

Happen to know the specs you're talking about?
edit:

Found em:

Float level 12.5mm
Main jet #90
Slow jet #42
Idle mixture 1.5 turns out
Idle speed 1000 rpm, plus/minus 100
How do i measure it?

 

[VonYinzer]

Not being a jerk... Promise... You need a manual.

 

[Bert Jan]

Not being a jerk... Promise... You need a manual.

i Have 2. But you're right. I should have checked them first. my bad. thanks anyway!

 

[VonYinzer]

All good man. The manual doesnt lie (usually)... The internet does. Haha.

 

[Bert Jan]

haha true true..

Well, i've set my floats to 22mm, as per manual.Still leaking as fuck. Going mad on this one.
When i push the starter button (turning the engine) it's even worse.

I know that when i bend the hinge in such a way that the needle is pushed in all the way it does NOT leak and i get no fuel in the bowl at all. That tells me the needlething works. I really don't get why it doesn't shut the damn thing close when bowls are full. I adjusted the hinge thingy in a lot of ways, i guess from 25mm all the way up to 20 (mm at a time) but no cigar. damn. what is it?

 

[Bert Jan]

did some google-ing. Most familiar problems are caused by worn float needles and such. Could mine be worn? I guess not since they do close appropriatly when pushed in all the way (by bending the hook on the hinge..)
As they are 30$ a set (x4) i'm not really in the position to 'just buy' new ones hoping they'll work. I'll buy them when i'm sure it's a solver.

lost here, please help.

 

[teazer]

Another problem that occurs on some bikes is that the fuel overflow tube cracks and then they leak. Remove #3 bowl and put it on the bench with a drip tray underneath and fill it with fuel to almost the top of the overflow tube. If fuel is leaking out, the tube is cracked. Get thin wall brass tube from hobby store to slide over the existing tube.

Repeat for #4. report results.

 

[Bert Jan]

Sweet, thanks. Will do!

 

[Bert Jan]

Soooo, i went at it again last night.

Took off the bowls and checked the copper overflow tubes for hairline cracks. Layed the bowls on the bench, filled em completely with fuel and layed a piece of toiletpaper underneath to see spill. Bone dry after 15min on both bowls. Tells me tubes are ok.

Took off needles and needle seats and boiled them in lemonjuice. Put on new o-rings and cleaned really good wih clean fuel to remove any citric residu.

Checked floats for leaks. Put them in a container filled with 15cm of fuel and then i used bike spokes to keep the floats on the bottom. Waited 10 minutes and as soon as i released the spokes the floats came up. pushed them underneath couple of times in different angles, but all is good with them.

Checked if hinge-axle was worn, causing floats to get stuck. Polished the axles, cleaned the holes in the floats and it's buttersmooth.

Took the needle and seat, pushed fuel line over the seat and let fuel in the tube while needle was in. Checked closing ability with my fingers and they both work like a charm. The smallest amount of force is needed to shut the valves. Even with the spring-tube on the needle not even pushed in i made a perfect seal.

Then, i turned on the fuel for a second to remove any residu from carbs.

Put needles and seats in carbs and turned on fuel while both needles were pushed in. Bone dry. Nice.
Put floats in, measured again on (per manual) 22mm and made sure they pushed the needles.

Holding the floats up, i turned on fuel. Bone dry. Nice.

Screwed on the bowls, turned on fuel. Niagara falls. Damnit.

Took them off more then 20 times to make minor adjustments from ALL (14mm) the way up to ALL (28mm) the way down, but to no avail.
Even turned floats upside down, cause i know it's something simple and just tried. That didn't work either because the float has no movement and pushes the needle in all the time. Bowls were dry that time around btw, so that again tells me needle seatings are good.

carbs 1/2 and 3/4 are connected with fuel t-pieces and a little plastic tube (nrs 1 and 3 in red). What is that? The 2 inner carbs have tubes pointing upwards (nr 2 in red) and carb 3 is gushing fuel out of there as well.

Am i chasing my tail, are the Keihins pulling a trick on me or do i need new carbs?

Please doctor Phil, i'm losing it!

 

[Bert Jan]

Bike is done atlast, except my 1:4 ratio on milage. Please help me, i wanna ride!
Going to pull the carbs off the bike today. Boil everything in lemonjuice, replace all rings again and hope for the best.

 

[teazer]

The good news is that you removed one possibility and that's progress in the big scheme of things.

Are you sure that you are measuring the float level the right way? It should be on an angle and measures to the gasket surface (typically) despite how it's shown in manuals.

On older carbs we used to have a problem with the gasket squeezing into the bowl slightly and just touching the floats, so they stuck open with a bowl on and were fine when you pulled the bowl off to check. Those use an O ring IIRC so that shouldn't be the issue here.

On co-joined twins, if one floods, its partner also floods, so it may just be one problem carb in a pair.

Is there any possibility that some of the bowls are different and something is touching the floats? A quick check is to attach a clean hose to the feed side and blow in as you tilt the carbs (after they are drained of course) to see if they shut off as they are tilted forwards to raise the floats.

 

[Bert Jan]

Thanks teazer, good advice!

I tore the carbs off the bike today and took em apart. Completely. Boiled them in citric acid and they're drying as we speak.
Assemble comes tomorrow and i hope they're dry. using new o-rings, gaskets and stuff.

measuring the floats as follows:

Tilting carb in such a way that float is barely touching needle, spring not compressed. 22mm from top of float to flat o-ring surface on body. that's how it's done - right?

 

[Bert Jan]

Decided to take em off the bike and clean really good. used new orings and such and hope for the best:

lemon juice and citric acid FTW!

funky funky! (smell that is)

found out all floats were off like mad. Adjusted them the right way:

Not touching needle:

Tilt carb until float touching needle:

This should be 22mm when carb is held in angle from above photo.

Hmmm pretty!

More blue to come...

yeah i know my bowls are the wrong way on. don't care, those brass bolts don't come off evah again

 

[teazer]

All looks fine but the floats look to be too high (close to the body) to me. I expect to see them more or less level withteh bottom of the main jet holder.

Do you have a spare float bowl by any chance? I'd love to break off the overflow tube inside the bowl and attach a length of hose to the external portion of the overflow tube to see the actual height of the fuel. Sometimes known as the WET level. It should be around 3mm below the gasket surface.

 

[Bert Jan]

Hey Teazer, nope, dont have a spare bowl. (I once bowled a spare though )
It's all good, carbs are dry and bike runs likea champ!

Thanks all for your help! This site kicks ass!

 

[Bert Jan]

Motherfucker started again this afternoon...

Now what? It's nr1 and nr2. They're leaking so hard out the overflow tubes, i would lose a pee battle against em..
My knowledge tells me it can't be the worn float needles. It would be impossible to leak that much just because of a worn needle. Second, they started to leak without warning. Worn needles would leak more and more over time.

They're also leaking A LOT out the air overflow thingy (the nr2 thingy in the picture above)

Now, i'm no sure if this is relevant, but my girlfriend took the bike for a ride and forgot to turn the petcock on after a pause. result: Carbs went dry, bike stalled, leaking started.

I'm done with this shit. 4 options, want your opinion.

1. Buy new carb kits including needles, valves and everything ($ 100 total)
2. Buy secondhand carbs (same year, could be worn also..) ($ 30)
3. Buy carbs from newer bike and make em fit. I have the skills to do that,but it's a long haul.
4. Save money for CR's and don't ride for 557326 weeks. (Well, that's not an option is it )

 

[teazer]

Set of spare carbs gives you 4 spare bowls to work with....

Ran out of gas sounds like the debris in the bottom of the tank was sucked into the carbs and is jamming the float valves open.

 

[Bert Jan]

That's likely to be the problem. I checked the leaking carbs and cleaned the needles again. Screwed them back in and it's leak free.
Ordered 4 new float valves and needles. Also ordered a new fuelfilter to keep em new. fingers crossed.