Topic: Carb question ohhh.

[Duanob]

Your carb doesn't have to come apart but you have to seperate the carbs from the rack which is more of a pain then tearing into your carbs. trying to fit the fuel lines and Tees back together on all four are a excersize in frustration.

[flybox1]

I am having a similar problem. My number 2 is leaking. I have banged on it to no avail. I ordered a gasket, hoping that was all it was. But I had it over at the mechanics for a bit and he assures me it is an O Ring. I have been looking for a good video but all I can find for these carbs is how to clean them. Just read through my clymer's chapter on Carbs and it doesnt show specifically how to access the O Ring at the T. I was hoping for a simple fix, but it is looking like the whole carb may have to come apart to access that O Ring. Unless one of you fine folks can help us out.

how do you know #2 is overflowing because of the o-ring?
where is it exactly leaking from? gasket seam or overflow tube?
did you set the float correctly so the float valve shuts?
does your float valve even close properly to shut off fuel?
did you check the stand pipe for cracks?
if you have brass floats, are they leaky?

lots of stuff to do before tearing carbs apart...and like Duanob stated....is frustrating.

[Anti-Johnny]

how do you know #2 is overflowing because of the o-ring?
where is it exactly leaking from? gasket seam or overflow tube?
did you set the float correctly so the float valve shuts?
does your float valve even close properly to shut off fuel?
did you check the stand pipe for cracks?
if you have brass floats, are they leaky?

lots of stuff to do before tearing carbs apart...and like Duanob stated....is frustrating.

basically I took it to the mechanic and he felt around on the T connector that goes between the first and second carb. He said it should be very rigid and in my case it is loose.  As far as I can tell its leaking from the rear of the carb. To me it seems like from the gasket, but I cant be sure. As far as floats go, I have no idea. I took the bowl off and jiggled the float around but I dont know how to tell if it is freely moving or not. It is a pain to even see under there. I am going to go buy a little mirror today and see what I can see.

I dont even know what the stand pipe is. My clymers manual is a little oblique when it gets the part describing the carbs. I have a video on one of my threads of the leak. if I can get the gasket back in, I will try and record another.

This is the first bike I have ever worked on. I have some automotive experience but these carbs are super tiny.

[flybox1]

basically I took it to the mechanic and he felt around on the T connector that goes between the first and second carb. He said it should be very rigid and in my case it is loose.  As far as I can tell its leaking from the rear of the carb. To me it seems like from the gasket, but I cant be sure. As far as floats go, I have no idea. I took the bowl off and jiggled the float around but I dont know how to tell if it is freely moving or not. It is a pain to even see under there. I am going to go buy a little mirror today and see what I can see.

I dont even know what the stand pipe is. My clymers manual is a little oblique when it gets the part describing the carbs. I have a video on one of my threads of the leak. if I can get the gasket back in, I will try and record another.

This is the first bike I have ever worked on. I have some automotive experience but these carbs are super tiny.

does that T looseness equate to leaking?
maybe, maybe not.
if your carbs are completely dry, turn on your fuel and see where it leaks from.
the floats act as a lever, and close the fuel supply when fuel level rises in the bowl.
if they do not close the fuel valve (by having a malfunctioning fuel valve, a poorly calibrated float height, a cracked standpipe, or a leaky float) and the bowl continues to fill, fuel will flow out the standpipe(the brass pipe/tube in the bowl) and out one of the overflow tubes.
if the standpipe is cracked, you'll always have fuel leaking out the bowl, whether fuel flow has been shut off or not, and you'll always be battling float heights because never enough fuel fills the bowl..

I would suggest pulling the carbs off your bike(easier to work on) and rigging up an external fuel supply.
with the carbs supported and level, turn on the fuel and see where the leak really is.
then we can dig into the rest of the carb refurbishment...

[Anti-Johnny]

I hope I am not hijacking this thread. Just seems like a similar problem.

I just shot this video. The float and the float valve seem to be moving freely. I dont know if the float is in or out enough though. I can just see that it does slide up and down.

Its not in the video but when I hold the float up, even with the gas on, there is no leak. I dont know if this excludes the O Ring.

The second video is looking up from the bottom after I had the gas on for a few seconds to fill up the bowl. I can see that the leak is coming out from the gasket. This is the same old gasket that was in there and I may have not seated it properly. I need to get some grease to hold it in. So hopefully this may still mean it is just the gasket?

The stand pipe doesnt look cracked.

I can see in this picture that there is nothing attaching from the float valve to the float. In some videos, I see that there is a little loop of metal, but those may have been from different carbs.

I am waiting on my bike cover to come in before I take the carbs off. I park in covered parking and I dont want anything to blow up inside the engine. I plan on taping off where the carbs connect anyway, but just in case.

[Duanob]

"The stand pipe doesnt look cracked."

Look really close or plug one end and blow through the other.

Read this in the FAQ Carbs section.

Submitted by Aaron J Williams:

Superior and when he got back he told me that 1&4 carbs were dripping fuel. Since I had replaced sunk floats on 1&4 I suspected that the used floats I put in were sunk also or the float level was a little too high. I checked the floats and level but both were spot-on. I lowered the levels to see if I could stop the problem but the dripping continued. This morning I decided to put 2 different used floats in and see what would happen but when I removed the float bowls they were almost empty. A closer inspection revealed this: There were vertical cracks up the side of both float bowl overflow tubes! I took some bowls off of parts carbs and one of them was cracked too. After replacing the bowls with good ones the bike no longer drips. So if you can't stop your bike from dripping no matter what you do, look for cracked tubes.

Some suggestions as to fixing this without replacing the bowl:

•Solder
•JB Weld

Anyone actually tried this with positive results to share?


Aaron came up with this:

Ok, here's what I came up with for a solution. I took a piece of shrink tubing for 18 to 20ga wire and cut it to 29/32nds and put it over the cracked brass tube. After shrinking it on I put it in carb acid for 1 day to see how the tubing would hold up. The acid swelled the tube enough to slide it off the brass but after a couple of hours it shrank back down and was tight on the tube again. I then put the bowl back on the bike and after sitting in gas for 2 weeks it shows no sign of degradation. I think this is a viable alternative to JB weld or soldering and it looks a lot cleaner too!

 
 
« Last Edit: July 24, 2007, 12:03:22 am by SteveD CB500F » 
 

[Mavryk03]

"no i didn't think of the intake o-rings i will have to check them i put new ones on last year when the motor was rebuilt "

You're fine then. Mine were 34 years old. All my rubber was/is dreid and cracked. Slowly replacing all when I get the chance. it's amazing how it effects the way things run.

I wouldn't bet the seafoam will help a sticky float. it may clean out the float valve seat. You can pull your bowl plugs and use something long and skinny to poke around at the float. If it is a stuck float you will know it.

yeah i know it not a permanent fix just a quick one just wanted to get a couple of rides in before it gets too cold.  so can you send me a pic of your carbs with the stock airbox i cant get mine to attach to the carbs pain in the ars, i don't know if i have the wrong airbox or pieces if not don't worry about it i can look it up on the net thanks

[Mavryk03]

alright so spent sat messing around with the carbs and out the original airbox in but it was not the right airbox it said 550f on it so p/o had the wrong airbox in the first place, but got it fit and Little tape  now it runs better and still a little hard to get started on first start but it ran. floats seem not to be sticking really anymore put some seafoam in the tank so don't know if that helped Little. so took her out for about an half hr and everything ran fine only thing after i get into 3rd higher gears and go to downshift it want shift back down into 2 or 1 in less i use my hand to really out some pressure on it, so just another little problem, and took her out sun and was riding and saw some oil was leaking out of the head somewhere it was all over the front of the head so got to look at this now  it's a never ending battle lol but i did get her run and ride that makes me happy, so there are different airbox designed for the f and k model right if so i need to find a k model airbox?

[flybox1]

got a wife or GF?
stick a tampon or two between the fins to soak up the oil 
go for the 'heavy' if you plan on riding long  change after each ride.
-or-
you could try and re-torque the head, and see if that helps. 

[TwoTired]

alright so spent sat messing around with the carbs and out the original airbox in but it was not the right airbox it said 550f on it so p/o had the wrong airbox in the first place, but got it fit and Little tape  ....
 but i did get her run and ride that makes me happy, so there are different airbox designed for the f and k model right if so i need to find a k model airbox?

All the 550s had 550F cast into the air box.  It was first developed for manufacturing using the Cb550F production project.  But, the same unit was used on all 550's 74-76. 
The Cb500 71-73 (U.S.) had a slightly different design. The 77-78 used the same filter box, but a slightly different air plenum.
The mold designed for the CB550F air box was the master mold for nearly all of them, as there was simply no need to make another mold just the change the engraving done to the mold. 

Honda used a "parts bin" approach when making new models, often using parts originally made for another bike or model on the most recent bike or model.  One example is that the CB500 used a lot of the CB350 clutch.  There are lots more. 
The center three numbers in the Honda part number are the product code for the bike it was first used on.  323 is the Cb500 code, 374 was the early 550K model designation, and 404 was the late model Cb550K designation.  The Cb550F models were all 390 product code.

For example, the oil filter housing has a 300 product code listed in the parts catalog for the CB550F.  The 69-70 CB750 had the product code 300.  Now you know why most of the SOHC4's share the exact same oil filter type.

Cheers,

[Mavryk03]

got a wife or GF?
stick a tampon or two between the fins to soak up the oil 
go for the 'heavy' if you plan on riding long  change after each ride.
-or-
you could try and re-torque the head, and see if that helps. 

almost have a wife getting amrried next year,  will that really work of you just pulling my leg b/c that would be funny riding along with cotton tubes stuck in the finns and i though about re-toequeing it down as well. B/c i check the oil level after i got back and it was fine but it seemed like alot was coming out i also put some lucas oil in it suppose to help with lubbing the engine and stuff like that.

[flybox1]

yeah...no joke.
also heard of sections of cotton rope being used as well.
but why not use something that was MADE to be absorbant?

[flybox1]

...nothin' to be ashamed of 

(...your bike being on the rag.  sooner or later it happens to all of us with these old girls  )

[Mavryk03]

alright so spent sat messing around with the carbs and out the original airbox in but it was not the right airbox it said 550f on it so p/o had the wrong airbox in the first place, but got it fit and Little tape ....
 but i did get her run and ride that makes me happy, so there are different airbox designed for the f and k model right if so i need to find a k model airbox?

All the 550s had 550F cast into the air box.  It was first developed for manufacturing using the Cb550F production project.  But, the same unit was used on all 550's 74-76. 
The Cb500 71-73 (U.S.) had a slightly different design. The 77-78 used the same filter box, but a slightly different air plenum.

so i must have the wrong rubber piece that come from the carbs to the box, i though these were the right one they were the only ones i had, from the p/o but they must be wrong b/c the airbox wont fit right the clutch cable part that connects tie engine gets in the way and the left and right sides don't go on all the way so i had to do a little tape job to keep the carb and rubber cover so no air went out, it worked but i don't want to leave it like this.

[Mavryk03]

...nothin' to be ashamed of 

(...your bike being on the rag.  sooner or later it happens to all of us with these old girls  )

thats funny i might just do that not many more days of good riding left her in Indy thanks flybox your the best, oh and what i said about the shifter that would prob be internal right so i would have to take everything apart to get to it right?

[flybox1]

Mav - clutch 'tuning' isnt my cup-o-tea.
hopefully someone else can jump in here.....

[Mavryk03]

thats cool i think twotired knows a thing or two so maybe he will chime in thanks again for all you help.

[TwoTired]

Do you know which model of donor bike you have?

The filter holder box is the same for the 74-76 Cb550K and the 75077 Cb550F.
The 77-78 CB550K had PD style carbs which were longer and of a different inlet size.  This meant that the carb to plenum rubbers were shorter and there may have been a different spacing of the holes in the air plenum chamber, too.  I haven't looked at them side by side yet, I'll go look in my parts bin.  But, I need to address a leaky roof first.

The 77-78 Air plenum chamber does have a different part number than the other models.  Perhaps there is more difference than just the carb couplers that were glued on and part of that assembly.

It also matters how the filter box is attached to the frame.  The right angle pieces must be in the correct location and orientation for things to line up correctly.

I don't really know what you have, so it is hard to be precise.

Cheers,

[Spanner 1]

Seems like there are several folks asking Q's here in this thread ...
Anti-Johnny.... if gas is coming out at the bowl seal and the bike is sitting level, then the bowl is overfilling as the correct fuel level is below the gasket.  The gasket gets flattened over time and it's clearance to the side of the float is very small, so your float may be fouling against the gasket. It's easy for the gasket to bend-in at the sides too while your trying to get the bowl back on.  From your pic. the 'tab' on the float is all rounded, should be flat and top surface polished. That rounded shape would tend to push the float needle sideways causing it not to close properly IMO...... be sure to set the level at 26mm too, good luck.

[Mavryk03]

Do you know which model of donor bike you have?

The filter holder box is the same for the 74-76 Cb550K and the 75077 Cb550F.
The 77-78 CB550K had PD style carbs which were longer and of a different inlet size.  This meant that the carb to plenum rubbers were shorter and there may have been a different spacing of the holes in the air plenum chamber, too.  I haven't looked at them side by side yet, I'll go look in my parts bin.  But, I need to address a leaky roof first.

The 77-78 Air plenum chamber does have a different part number than the other models.  Perhaps there is more difference than just the carb couplers that were glued on and part of that assembly.

It also matters how the filter box is attached to the frame.  The right angle pieces must be in the correct location and orientation for things to line up correctly.

I don't really know what you have, so it is hard to be precise.

Cheers,

Hey twotired yeah i have the airbox pieces but the rubbers are my problem. i looked some up to see what they look like and i def have the wrong ones. the ones that i have now are only about 1 in wide so thats why my plenum chamber wont fit right and it hitting my clutch cable so i need to find the corrct rubbers for me bike.

[TwoTired]

Below is my 78 CB550K with the PD carbs and the proper air plenum and rubber couplers.
Resting on the spine is an Air plenum and rubber couplers for the earlier style carbs.

I don't have a 77-78K plenum off the bike to measure, but the hard plastic seems to be the same as the earlier style.  It is just the rubber couplers that I know are different.

The clutch cable routes between the #3 and #4 rubber couplers, as you can see.

Cheers,

[Mavryk03]

Below is my 78 CB550K with the PD carbs and the proper air plenum and rubber couplers.
Resting on the spine is an Air plenum and rubber couplers for the earlier style carbs.

I don't have a 77-78K plenum off the bike to measure, but the hard plastic seems to be the same as the earlier style.  It is just the rubber couplers that I know are different.

The clutch cable routes between the #3 and #4 rubber couplers, as you can see.

Cheers,

Ok i see now, like i said i though the rubbers were the wrong ones that were on my bike, but i found the right ones like the one in your picture, i didnt know what they looked like but now i do and found them in the bottom of a box of parts i had didn't know what they were but now i do  thanks for your help, got another question but not about this so i will PM you about it. thanks everyone for your help. Matt