SuzukiSavage.com - carb o ring doesn't fit -> gas leak in airbox

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carb o ring doesn't fit -> gas leak in airbox
12/09/24 at 22:28:13

Hi Folks !

First time here, first topics, I'm not used to write on forum.

Excuse my french, I'm writing from Tahiti so I may not use exact technical word.

I've looked into topics before I wrote and I didn't find solution so I hope you guys can help me.

I bought S40 Boulevard 650 cm3 six months ago here in Tahiti. I guess this model comes from US or Canada because some security stickers mention Canada. Motorbike is 12 years old but only 14.000 km. A retired woman kept it for a long time without driving it. First months were fine, only some noise (like bang !) when I was reducing speed. I brought it to my mechanic guy I deal with since more than 10 years.
He couldn't turn the screw to mix air/gaz. He was scared to break it so he left it like it was. Until there, not a big deal.

The o ring from motorbike fork had to be changed so I ordered it in France and left my bike at the garage. After 1 month (yeah we're far from everything), the piece arrived, I tried to start motorbike to bring it to the mechanic guy. Impossible to start. I looked under the bike and something was leaking. I managed to bring it to the guy and he told me there was a problem in the carb : the gas is leaking into the airbox.

I ordered new needle with o ring of course, waited 1 more month. and brought the piece to the guy. He called me the same day to tell me there was a problem : gas was still leaking because the o ring is smaller the the previous one. I thought it was a mistake, maybe there's a difference between europe and US models so I bought a new o ring from a shop in LA (Moto United, nice service, thanks Ivan !) and it's the same ... You'll find enclosed pics from the old oring.

Well, now here's my question : do you think there are different kind of oring for carb, or maybe different carb ? I start to think that previous owner maybe changed carb. How can I be sure it's a genuine suzuki S40 carb ?

And final question, What can I do ??? I love my S40 but I'd rather ride it than look at it.

Thanks for your help !

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ThumperPaul

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Re: carb o ring doesn't fit -> gas leak in airbox
Reply #1 - 12/10/24 at 04:46:13

Welcome to the forum. Tahiti sounds nice.

That looks like the correct needle valve seat for the stock carb (Mikuni BS40SS). See this thread with a carb diagram (see part/set #20).

http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1098869040

Are you buying genuine Mikuni parts (or cheap aftermarket parts)?

I can’t tell from the photo, but the o-ring does NOT appear to be the wrong size (maybe it is).

Did you also replace the actual float valve needle? The tip of the needle and o-ring needs to be high quality (like genuine Mikuni). It should be made of Viton (or something high quality), and not just ordinary rubber. A strong suggestion is to always use genuine Mikuni parts.

Since the carb flooded into the air box, you should also check the crankcase and see if gas is mixed into the oil. Remove the oil fill cap and check if you can smell gas. Even if you do not smell gas, you may want to drain the oil and check it to be safe.

Here’s a link to the jets page for the Mikuni BS40SS carb. Look around this website for the float valve and other parts (authentic Mikuni). I don’t have time to look around right now. I don’t know if they have shipping to Tahini.

https://www.jetsrus.com/a_jets_by_carburetor_type/jets_mikuni_BS_series.htm

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ThumperPaul

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Re: carb o ring doesn't fit -> gas leak in airbox
Reply #2 - 12/10/24 at 05:06:09

See parts 19-21.

#19 - SUZUKI OEM NEDDLE VALVE O RING | 13374-35C00

If you are sure it’s the wrong size o-ring, you may just want to try a local auto parts store and buy an assortment of “gas resistant” o-rings. I’ve never actually measured it.

https://www.partzilla.com/catalog/suzuki/motorcycle/2006/boulevard-s40-ls650/...

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ThumperPaul

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Re: carb o ring doesn't fit -> gas leak in airb
Reply #3 - 12/10/24 at 05:33:09

Great point about the petcock valve, Dave! I forgot that the vacuum line could allow gas to pass through it and into the carb from above.

One more thing to check is the float itself. If it has a hole or crack, it won’t float and the valve will never close. If the mechanic is any good, this should have been noticed.

It’s interesting and worth noting that Cool Ruler thinks it has to do with a wrong o-ring size. Just a few mils too small (or too big ID) is enough to cause a leak.

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« Last Edit: 12/10/24 at 19:14:36 by ThumperPaul »

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Tocsik Serious Thumper Offline the singularity Posts: 1206 Denver, CO Gender:	Re: carb o ring doesn't fit -> gas leak in airbox Reply #4 - 12/10/24 at 18:02:01 Definitely check that petcock. I honeymooned in Tahiti and Moorea. Beautiful. Hope you get the bike running to that ring road around the island!
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Cool Ruler

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Re: carb o ring doesn't fit -> gas leak in airbox
Reply #5 - 12/10/24 at 22:55:41

Thanks for your answers both of you.

@ThumperPaul : You're right, th needle valve seat is the one we removed from the motorbike with the original o ring. Now, both oring purchased from Europe and US are the right size, I mean diameter, but not the thickness (hope it's understable) so when we put it back in the carb, it's moving inside, which explains the leaking.

To answer your question : I bought genuine parts (from Us and Europe)

I thought maybe the previous owner changed the card. But no (see picture under).

So I got a genuine Mikuni carb, I got a brand new genuine oring (#13374-35C00) but it doesn't fit the genuine needle valve seat.

Even Suzuki shop staff here in Tahiti don't know what to do, except maybe to buy a new carb Wink

In fact one of the guy suggests, like you did, to find a oring from automobile part shop.

Well yeah, but is there any chance to find the right dimension (external at least) or should I go to try any oring ? Will take time.

Again, thanks for your time and if you have any idea, fell free to share.

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Cool Ruler YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 4	Re: carb o ring doesn't fit -> gas leak in airbox Reply #6 - 12/10/24 at 22:56:23 oring
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Cool Ruler YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 4	Re: carb o ring doesn't fit -> gas leak in airbox Reply #7 - 12/10/24 at 22:56:53 oring brand
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