Author Topic: Carb leaks at fuel line inlet "T" junction on right side. Cause? Part Supplier? (Read 9146 times)

Cut · « **on:** June 22, 2012, 12:37:05 PM »

Cohorts...I just rebuilt the carbs on my 1975 Honda CB550. After opening the petcock, I see that I am leaking fuel badly from the "T" junction on the right side. I installed new 1/4 inch fuel lines and report that it is not leaking from around the fuel line, but rather the right side of the "T" that feeds the carbs (this would be carb#3). Looking for advice from seasoned CB pros to isolate the cause of the problem (O ring seal perhaps) and www. sourcing for replacement parts. No...I am not leaking from the float bowls, simply around the right side of the "T" junction.

Thanks in advance fellas.

Johnie · « **Reply #1 on:** June 22, 2012, 01:02:47 PM »

I just replaced those on my CB750KO. Not sure if your part number is the same, but a fellow member got some metric ones from NAPA which worked fine. I bought the same ones and they are good. I could give you that NAPA part number, but I am not sure it is right for your bike.

Duke McDukiedook · « **Reply #2 on:** June 22, 2012, 03:15:48 PM »

Make sure it is just the o ring and not the T itself that might be cracked, I think they are phelonic.

Cut · « **Reply #3 on:** June 22, 2012, 03:40:49 PM »

Copy all...and thanks for the wisdom. Will look to inpect/replace either the "T" junction and or the seal which may be "phelonic" aka afixed to the "T" junction. Yes, I had to look up phelonic to determine its meaning. Will leak test prior to reinstall. P.S. She never leaked prior to soda blasting. Think we need to warn the masses on this so that they stay away from this sensitive area.

The term "phenolic" is used to refer to a few different substances made with phenol, an organic compound. It can describe a type of resin used to create various consumer items and is the name given to a class of plant-based chemical compounds. It can also refer to carbolic acid, an organic material that has been used in various medical and cleaning products. "wiseGEEK.com".

Bodi · « **Reply #4 on:** June 22, 2012, 07:53:20 PM »

I had an O-ring fail, piddling gas from one of the non-tee fuel junctions when I did my spring start-up. I fear it's the ethanol in fuel that's degrading the OEM rubber. I buy Shell premium now- only gas around here with 0% ethanol.
I was surprised that one broken O-ring would cause a fuel leak. I replaced all four on each junction, but only one (where it leaked) was actually broken. All of them seemed pretty stiff. The bores looked fine. I believe I previously replaced all 12 of these O-rings about 15 years ago. All have been nitrile, from Honda carb gasket kits. I would suggest Viton if ethanol fuel is used.

HondaMan · « **Reply #5 on:** June 22, 2012, 08:22:59 PM »

Those Tee O-rings are 2x8mm size. If you can't find them locally, PM me and I can sell you a set: I have about 100 of them from rebuilding these carbs en masse this last winter!

lucky · « **Reply #6 on:** June 23, 2012, 04:07:11 AM »

Quote from: Cut on June 22, 2012, 12:37:05 PM

Cohorts...I just rebuilt the carbs on my 1975 Honda CB550. After opening the petcock, I see that I am leaking fuel badly from the "T" junction on the right side. I installed new 1/4 inch fuel lines and report that it is not leaking from around the fuel line, but rather the right side of the "T" that feeds the carbs (this would be carb#3). Looking for advice from seasoned CB pros to isolate the cause of the problem (O ring seal perhaps) and www. sourcing for replacement parts. No...I am not leaking from the float bowls, simply around the right side of the "T" junction.

Thanks in advance fellas.

You can get new O rings at NAPA auto parts.
P/N 727-2605
8mm ID and 12mm OD .....2mm thick. LUCKY

lucky · « **Reply #7 on:** June 23, 2012, 04:09:34 AM »

Quote from: DukieFrankenkit on June 22, 2012, 03:15:48 PM

Make sure it is just the o ring and not the T itself that might be cracked, I think they are phelonic.

They are not plastic on the CB's, Not back then thank god.

VF and VFR's had the damn plastic crap.

bollingball · « **Reply #8 on:** June 23, 2012, 04:28:02 AM »

Lucky can you tell me where you found this 8mmX12mm measurement. I like to find this stuff for my self but don't know where to find the CORRECT numbers. Also if you take 8 from 12 would it be 2mm thick or 4mm

Quote from: lucky on June 23, 2012, 04:07:11 AM

Quote from: Cut on June 22, 2012, 12:37:05 PM
Cohorts...I just rebuilt the carbs on my 1975 Honda CB550. After opening the petcock, I see that I am leaking fuel badly from the "T" junction on the right side. I installed new 1/4 inch fuel lines and report that it is not leaking from around the fuel line, but rather the right side of the "T" that feeds the carbs (this would be carb#3). Looking for advice from seasoned CB pros to isolate the cause of the problem (O ring seal perhaps) and www. sourcing for replacement parts. No...I am not leaking from the float bowls, simply around the right side of the "T" junction.

Thanks in advance fellas.

You can get new O rings at NAPA auto parts.
P/N 727-2605
8mm ID and 12mm OD .....2mm thick. LUCKY

Ken

Bodi · « **Reply #9 on:** June 23, 2012, 05:52:23 AM »

8mm x 2mm would be 12mm outside diameter. That's the 2mm on both sides.

Johnie · « **Reply #10 on:** June 23, 2012, 05:55:53 AM »

Regardless the measurements...the P/N Lucky posted from NAPA are the ones I used and they are good. That part number was provided on this board back in 2006 from another member.

lucky · « **Reply #11 on:** June 23, 2012, 02:19:29 PM »

Johnie is very sharp!!!

bollingball · « **Reply #12 on:** June 23, 2012, 06:42:41 PM »

Thank all of you very much. I am still trying to figure out why Lucky's measurements are different than HondaMan's How do I figure out which one is correct? Or am I missing something?

Ken

lucky · « **Reply #13 on:** June 23, 2012, 10:19:14 PM »

Just buy Hondamans O rings.

754 · « **Reply #14 on:** June 23, 2012, 11:07:00 PM »

Sizes are listed in the HONDA partsbooks...

HondaMan · « **Reply #15 on:** June 24, 2012, 12:10:16 AM »

Quote from: 754 on June 23, 2012, 11:07:00 PM

Sizes are listed in the HONDA partsbooks...

They are, but keep this in mind: Honda lists the MINIMUM size that will work. The numbers they show as the results are not always direct cross-overs to standard sizes. The carb Tee O-rings show as 1.9x7.9mm, for example, when the 2x8mm is the standard size. That was just how their 'system' worked, back in the 1960s and '70s.

DedHed · « **Reply #16 on:** June 24, 2012, 05:20:42 AM »

Back in a previous life, I worked for a gasket and hose company and remained friends with the owners of the company. They keep a stock of o-rings on a section of shelves that is around 10' tall X 30' long, everything from viton to buna. From what I remember, there should be a tiny bit of space left in the groove after the o-ring is installed, the groove is square and the o-ring is round. When the o-ring is installed in the groove, it is a tiny bit streched, and therefore the diameter is reduced. A properly sized o-ring is installed and sealed, it will compress to a square thus causing a flat sealing surface. Having said that, I would buy the o-ring from Hondaman if you have any doubts. If'n you have the tools to measure the groove width (o-ring diameter), goove diameter O-ring ID), and the ID of the tube the grooved part will be sealing (O-ring OD), any industrial shop will have a chart indicating which o-ring you should use.
It's early and I'm only on my first cup of coffee so all of the above could be pure BS.
Phil

bollingball · « **Reply #17 on:** June 24, 2012, 06:09:54 AM »

Quote from: 754 on June 23, 2012, 11:07:00 PM

Sizes are listed in the HONDA partsbooks...

Well this sounds like it would be good to have. I looked at a few places on this site with no luck. does anyone have a link to find one.
Another thing I thought of how many are there. HondaMan and Lucky gave two different numbers so maybe one used his manual and the other used one for a different model. I would need one for a 78 750 K.
Thank you Lucky and HondaMan maybe this will help clear things up for others. And thank you 754 I did not one was out there that gave the measurements.

Ken

Bodi · « **Reply #18 on:** June 24, 2012, 06:15:59 AM »

"American" inch O-ring sizes were standardized for WWII production efficiency, and those standard sizes are still used. Unless there was a really good reason to have used a custom size, any inch O-ring you come across will be one of those 400 odd standard sizes. You can easily find a listing of these, and when ordering you use the part number like #377 (this is 10 3/8 x 3/16 btw) and the material desired. Even plumbing O-rings at Home Depot are labeled with the standard part number.
The closest inch cord size to 2mm is 3/32 at 2.38125mm, closest ID to 8mm is 5/16 at 7.9375mm. This 3/32 x 5/16 size is a #104 O-ring. That's probably close enough but will maybe be a tight fit on the cord diameter.
Metric ones are different. There are many thousands of sizes - a vast number of cord diameters and a vast number of ring IDs. Honda or KeiHin used the 7.9 x 1.9mm ring for reasons beyond knowing, maybe they had a big box of them lying around. 2 x 8mm is pretty much the identical size, close enough to not make any difference.
As far as I know KeiHin used the same fuel connector size on all multi-carb stacks.

bollingball · « **Reply #19 on:** June 24, 2012, 06:54:15 AM »

Quote from: Bodi on June 24, 2012, 06:15:59 AM

"American" inch O-ring sizes were standardized for WWII production efficiency, and those standard sizes are still used. Unless there was a really good reason to have used a custom size, any inch O-ring you come across will be one of those 400 odd standard sizes. You can easily find a listing of these, and when ordering you use the part number like #377 (this is 10 3/8 x 3/16 btw) and the material desired. Even plumbing O-rings at Home Depot are labeled with the standard part number.
The closest inch cord size to 2mm is 3/32 at 2.38125mm, closest ID to 8mm is 5/16 at 7.9375mm. This 3/32 x 5/16 size is a #104 O-ring. That's probably close enough but will maybe be a tight fit on the cord diameter.
Metric ones are different. There are many thousands of sizes - a vast number of cord diameters and a vast number of ring IDs. Honda or KeiHin used the 7.9 x 1.9mm ring for reasons beyond knowing, maybe they had a big box of them lying around. 2 x 8mm is pretty much the identical size, close enough to not make any difference.
As far as I know KeiHin used the same fuel connector size on all multi-carb stacks.

Can you give me a link to this? Is it a chart? I have been having to look them up one at a time it woul be nice to have a chart to look at.
Thanks Bodi

Bodi · « **Reply #20 on:** June 24, 2012, 02:51:46 PM »

well, here's one:
http://www.broadleyjames.com/o-rings-size-chart.html
searching "o-ring sizes brings up a few pages of them on google.

bollingball · « **Reply #21 on:** June 24, 2012, 07:42:54 PM »

Thanks Bodi that will come in handy

Cut · « **Reply #22 on:** June 24, 2012, 11:02:51 PM »

I installed the 2mm (Width) X 8mm (Inside Diameter) X 12mm (Outside Diameter) today and report that she no longer leaks. Napa only had one ring in stock, so I leaned on my buddies at Tractor Supply and they had as many as I wanted for 20 cents apiece. I did buy the only one that Napa had, so that I could confirm the size of the seals at Tractor Supply. Finally, another thread put to rest! Thanks Ya'll.

The Machine · « **Reply #23 on:** August 25, 2017, 07:50:04 PM »

Do you still have the Tee O-rings? I need 4 for my 75 Honda CB550

Johnie · « **Reply #24 on:** August 26, 2017, 07:40:41 AM »

Send Hondaman a PM by clicking on his name above...he may get to it faster.

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Author Topic: Carb leaks at fuel line inlet "T" junction on right side. Cause? Part Supplier? (Read 9146 times)

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