Topic: CB550 fuel leak between carbs, common?

[j squared]

I ran my bike for the first time today and noticed I had a fairly steady fuel leak coming from both sides of the bike, up above the float bowls.  After getting it home and looking at it while it was idling I am pretty sure it is leaking at the T where the two fuel lines come in and connect to the carbs, between 1&2 and 3&4. 

I circled where I think the leak is coming from, maybe bad o-rings?



Is this a pretty common place for leaks?  Im asking because I want to be 100% sure its not leaking where the fuel line meets the T, even though I checked and rechecked it Id rather not have to rebuild these carbs if at all possible   Just got this thing on the road and of course something like this happens!!  Argh.

Anyway, I did a few searches and didnt see anything specific to this fitting, if anyone could offer some advice that would be awesome!

[Stev-o]

I have a 550 and have not heard of this issue.

[fmctm1sw]

I had to put new o rings on those on my 350F after (naturally) I had the rack stripped to clean the carbs.  I buy fuel resistant o rings like that at Napa...

[Raef]

I don't know how common it is but i have had to replace them before. I just used some o-rings out of one of those o-ring kits with the assorted sizes.


It's a pain in the rear, but the job can be done in a day.

[Deltarider]

It's not common. Have you used hostile fluids by any chance?
Out of curiosity: do your T-joints have double O-rings on each side or just a single?

[bryanj]

Its very rare unless they have been stripped and damaged, more common is to put a nick in the pipenpushing it on

[KingCustomCycles.com]

The seals dry out and may reseal in a day or two with exposure to fuel.  Also, modern 1/4" fuel line is not what was installed originally on these bikes.  It is larger than the I.D. original.  I like to use a wrap of aircraft safety wire (brass) as a clamp for the main fuel lines at the carbs.  There is not enough room for screw clamps and the wire looks pretty old school. 

[736cc]

. You cannot avoid the fix because the leaking won't stop anytime petcock is open. On CB750's u need to remove carbs and seperate them from the rack to get to the T's. Those o-rings need to be fuel resistant and very hard to source the exact size in mm. Somebody on ebay was selling them a while ago; maybe search this forumn under carb T's o-rings

[Mavryk03]

On my cb550f when i rebuilt the carbs i out new o-rings on lines yours a prob just old and crusty, it is a pain to replace them but it's worth it good luck

[Kevin400F]

1.9mm cross-section x 8mm i.d.   Buna-N 70 Durometer.

I have plenty on hand, if you would like a set.  You'll need 8 rings (four per tee). 

Send me a PM on the Forum here, or shoot me an e-mail at kthunter01@sbcglobal.net

[j squared]

Thanks for the help everyone, I took a look today and I think one side has dried up but the other side is still leaking pretty bad.  I figure its not going away and might as well fix it now rather than worry about it later.  Ive never done any carb work before so no better way to get my feet wet I guess


So, if the rest of the carbs dont appear to be leaking, do you guys think its worth doing a complete rebuild to clean them out while I have them off?  Ive taken them off before and don't think its too hard, but I hear once you separate them from the rack thats the worst part, reassembly-wise.  Might be worth it to see whats in there after who knows how long since a bath.

1.9mm cross-section x 8mm i.d.   Buna-N 70 Durometer.

I have plenty on hand, if you would like a set.  You'll need 8 rings (four per tee). 

Send me a PM on the Forum here, or shoot me an e-mail at kthunter01@sbcglobal.net

I'll totally take you up on that, thanks man!!  PMing you now.

[Raef]

I would at least pull the bowls off and take a look and check the float heights, valve seats idol jets

Mark

[Deltarider]

Are you sure it's not leaking from between the fuel hose and the joint. That is common, as people sometimes use wider (6mm) than the 5,5 mm ID hose.

[j squared]

Are you sure it's not leaking from between the fuel hose and the joint. That is common, as people sometimes use wider (6mm) than the 5,5 mm ID hose.

I checked it twice but I am definitely going to check it again before I make the call.  The OP had some non-OEM fuel line on there so it may be too big.

I'll see about getting a small zip-tie on there to see if it stops, or using some brass wire like someone mentioned.  If that all fails, maybe get some new hose and run it back on there but Im sure getting it on that nipple with the carbs installed is not easy (maybe not possible).

[Deltarider]

When not sure where it leaks powdering the suspect spots with talcum powder can help to identify. Yes, it can be hard to shove the tube over the nipple. A bit of WD-40 sprayed inside the tube-end can help.

[j squared]

Im going to take a closer look sometime this week and see if I can pinpoint it for sure.  Where the T fitting is and where the lines connect to the T are so close though it was really tough to see before, Ill try some powder though and see if it helps.

[j squared]

Just an update for anyone paying attention  Found one side is still leaking after a few days of starting it after work and letting it idle for 5-10 minutes.  Whats more, last night I started getting really bad float overflow on at least two carbs, huge puddle of gas under the bike.  

Figure its time to pull these carbs and crack the bowls to see what is up in there, and also to take a closer look at the fuel line T's to see if I can spot the leak.  if nothing else I will be able to get the fuel lines attached properly with the carbs off and more room to work.



Side question: at what point should I think about resynching the carbs?  I have read some posts that say you should synch them any time you pull them off the bike, and that seems a little extreme.  I'd rather not have to buy a synch tool right now although I do want to get one eventually.  Just have other things that need to come first this month.


Edit:  One more question, if there any harm in filling the carbs with gas while they are off the bike to look for a leak and check the float function?

[KingCustomCycles.com]

no synch required unless you change something that effects airflow.  It is a great idea to test the carbs for leaks off the bike.  I put a can of gas 5 feet above the rack, level it on the bench with a 2x4 under the throats and look for drips.  That step saves hours of pulling and reinstalling on a drip that is hard to fix.

[Duanob]

Sounds like you will be pulling the carbs. Cleaning and new o-rings throughout is not a bad thing. Prevents further fuel leaking in the future. O-rings dry out, get brittle and crack. All of mine inside my carbs were just that. I feel better replacing and thoroughly cleaning them. The bike runs way better. You can check/set your floats, make sure your needles are set correctly, and bench sink the carbs and drive it that way until you can afford a syncing tool. If you get the Honda OEM carb gasket kit you get everything you need.

[j squared]

Thanks for the tips guys, you guys rock.  Going to be diving in tonight, once I get a closer look I will make the rebuild call but I'll probably end up doing it I'm thinking.  Just hate to have the bike down again for a few weeks after a total ride time of 10 minutes so far

[Duanob]

Get a gasket kit first then download the manual section on carbs and articles from the FAQ section about rebuilding and removing carbs. Also your blow up diagram up above will help a lot too. If I can do it, anybody can do it 

[j squared]

Well I pulled the carbs off and drained them, quite a bit of rust sediment came out of the float drain screws so I was expecting the float bowls to be really bad.  Pulled them off and they were pretty much immaculate haha.  Thanks, PO.  Cleaned some rust from the bottom and checked the tank, sure enough some rust had accumulated at the bottom between draining it over the summer and now.  Guess some clean up is in order.

Gave the float bowls and the jets a blast of carb cleaner and compressed air, pushed the fuel lines on the T's better and wrapped a small zip-tie around each line and reinstalled the carbs. Also checked the float heights and they weemed about just right.  Im going to run it tomorrow and see what happens, Im thinking (hoping) it should be OK.  If I have to pull them off again and rebuild so be it, I'll jump off that bridge when it comes haha.

[Deltarider]

If you remove the carbs from the bike and/or remove the float bowls for inspection there's NO need to synchronize afterwards. (To much syncing going on in this forum, if you ask me.)

[Duanob]

If you remove the carbs from the bike and/or remove the float bowls for inspection there's NO need to synchronize afterwards. (To much syncing going on in this forum, if you ask me.)

Sounds like syncing fixes a lot of problems on this board as well. If he doesn't know if they are synced then it's time well spent.

[j squared]

yeah it definitely wouldnt hurt and I probably would if the carbs ended up being dirty or if the bike ran poorly before.  Carbs were just cleaned it looks like and the bike ran great before it started leaking so Im guessing the PO just had them serviced/sync'd pretty recently before selling it.

Meant to take a look at the jetting since I have a 4-2, see if maybe he got it tuned for them or not.

[j squared]

Well good news, the leaks stopped at the fuel line T's  I think it was the line actually, pretty sure I used a 1/4" line instead of 5.5mm.  But its stopped, good good.

Bad news is my #4 float seems to always to overflowing any time the gas is left on with the bike not running for a few minutes. Going to run it for a bit and see what happens, might need to pull that bowl again and take a closer look.  Thanks for the help everyone, its running nicely once again!!

[Deltarider]

Good to hear. 1/4" line is definitely to wide as Honda used ID 5,5mm for the 550F and F1 and 5,3mm for the 550F2.

Bad news is my #4 float seems to always to overflowing any time the gas is left on with the bike not running for a few minutes. Going to run it for a bit and see what happens, might need to pull that bowl again and take a closer look.

Easy to fix. First tap the float chamber with the stub end of a screw driver. When you're lucky little particle(s) between float needle and seat will fall down, leaving the set unobstructed.
If not, floatchamber #4 is the easiest to remove of them all. You can now check 'live' by pushing the floatbody from underneath if the floatneedle closes. Watch closely and make sure the needle doesn't cant. If not remove seat and needle for inspection. If damaged replace, preferably by Honda Genuine Part.

[Duanob]

1/4" line is definitely to wide as Honda used ID 5,5mm for the 550F and F1 and 5,3mm for the 550F2.

Great! I just ordered some 1/4" line and 2 filters. After researching this board the consensus was naught! The 5.5 mm was impossible to find locally or super expensive to buy. $20+ for a couple of feet of OEM? Some guys said the 1/4" worked and others say no. Guess I'll find out soon enough.

As always, you get the experience...right after you need it!

[j squared]

Well it seems to be working fine now, just make sure you have it pushed all the way on the fittings, passed both flares on the nipple and tight.  The only place it looks to be a bit too big is at the float bowl drains, where the nipple is really short and only has one flare on it.  I used a small zip-tie there to keep the line tight on the fitting.

[TwoTired]

5.5mm line fits on the nipples without the need for clamps to keep it from leaking.  1/4 inch line does need clamps.

As to expense, the 5.5mm line only needs replacing once every 25-30 years.  That doesn't seem expensive to me.


As to carb sync. 
If there was a significant valve lash change; re-sync.
If the carbs were dismounted from the stay plate; re-sync.
If the slides were removed from the carbs; re-sync.
If there is ANY chance a PO may have messed with the sync adjusters or slide actuating linkage; re-sync.
If you suspect any of the 4 cylinders may have changed it's volumetric efficiency; re-sync.

In-line filters are only used when the in tank or fuel tap filter can't be restored.  Extra filtering gains you nothing but a future maintenance chore, and almost always disrupts the gravity feed system from tank to carbs.

Cheers,

[Duanob]

Well it seems to be working fine now, just make sure you have it pushed all the way on the fittings, passed both flares on the nipple and tight.  The only place it looks to be a bit too big is at the float bowl drains, where the nipple is really short and only has one flare on it.  I used a small zip-tie there to keep the line tight on the fitting.

I used 1/8" on the drain tubes, fit nice and tight with no clamps.

TT I'll use filters until I can address the dirt and rust in my tank. That will be my winter project to clean and paint. It's not bad but I found plenty of rusty sludge on my in-tank filter tube. After cleaning the carbs I don't want that sludge in there.

As far as carb sync don't forget, if you just bought the bike and don't know the history, a carb sync is a good idea as well.

[Deltarider]

As far as carb sync don't forget, if you just bought the bike and don't know the history, a carb sync is a good idea as well.

After you checked and doublechecked about everything else and you're still not satisfied with how the engine idles, yes.
When I read about all these bikes acquired with almost virgin odometers, I find it difficult to believe the POs have done much syncing or adjusting float heights. In itself these parts won´t lose their adjustment position when the bike sits for years. If they were untouched in this respect, they´re still in the adjustment position as where they were in when the bike was handed to its first owner. And if you don't know the history of the bike, there´s a good chance the four idle adjusters and float tabs are untouched.
Warning: if you start syncing to early, that means before you´ve adressed all the other maintenance points, you will go round in circles and never reach a fine running engine. That´s my point.

[Duanob]

"When I read about all these bikes acquired with almost virgin odometers, I find it difficult to believe the POs have done much syncing or adjusting float heights"

Yeah that's understandable. I wish that was my case. I have 23K+ miles and I had a PO that fiddle farted with things he shouldn't have. In my case I won't assume anything. Also there are plenty of cases where pods and headers and all that have been installed and then the jets are messed with and so on. Frankly I can't wait to try and sync my carbs if just for the experience. Now if I only had a gauge.

BTW I just got my 1/4" fuel line and filters in today so I will let ya'll know how it fits.