carb leak

carbs don't leak on prime or on, and my floats are set correctly (dry and wet).

when the bike is running however, gas is flowing fast out of the bowls on 1 and two. the gaskets look fine. any suggestions? fuel rail? the drain screws are close, i promise.

 

Either stuck floats or fuel supply tube o-rings........

 

weak, was trying not to have to break the rack

 

You're thinking of the wrong o-rings... You don't have to break the rack to get to the o-rings chacal is talking about. He's talking about the o-rings on the float needle valve seat and filter assy. I'm guessing that you're thinking of the ones on the supply tubes between carbs?

The needle valve, seat, filter, and o-ring are at the middle bottom of this pic:



Basically the theory is that fuel is supposed to flow through the filter screen and be metered by the needle valve as required by the float level, but if that o-ring is shot, fuel can go AROUND the whole needle valve assy (instead of through it) and get into the bowl even when the bowl does NOT need fuel.

Burnarr

 

Actually, now that I re-read... I may have misunderstood something. It may in fact be the o-rings on the supply tubes between carbs...

Is the fuel flowing fast OUT of the bowls, or fast OFF of the bowls??

If it's coming OUT of the bowls, then it's not the supply tubes. If it's dripping down onto the bowls from above, then if could very well be the supply tubes.

(Haha! Teach me to go sticking my nose into this thread!)

 

u know, im going to have to check.. i was soo excited that the bike started and maintained idle i didn't pay attention to where the gas was coming from....

but it looks like its coming from the top of the bowls (out of them, not the rail)

unfortunately, i need to make some new carb boots coz my airbox is bent and i don't get a good seal, so the test will have to wait till tomorrow.

I'll check those orings after i check where the leak is coming from. pray i don't have to break the rack....

BUT i have a feeling those filter orings could be it, since i used a lot of carb cleaner without removing those this time since i cleaned them so well the first time.

although, wouldn't the leak happen while on prime or while wet testing float levels if it were those o rings?

maybe it's my homemade gaskets, but they look pretty good. there's definitely a worse gasket in a carb that's not leaking....

so many questions. will have to experiment and get back to ya.

 

Dude, after removing and re-installing your cylinder head (twice), breaking the rack of carbs apart is ez-peezy........

 

yeah, but im lazy and would prefer not to, ESPECIALLY after breaking the head apart!!! =D
also, im better with big bits than i am with small.. sausage fingers....

any input on the questions above? the only happeneing while under vacuum perplexes me...

 

Yeah, gas flows so well and spreads so easy that sometimes it's really hard to pinpoint to true origins of leaks.

• If the leak is dripping down on top of the bowls from above, it's tubing or fuel supply o-rings.
• If the leak is seeping out of the seam between the bowl and the carb body, then it's carb bowl gaskets (duh).
• If the leak is running backwards out of the carb throat into the air box, then it's a float level issue or needle valve seat o-ring issue.

Personally, I would doubt it's the float seat o-rings. They may be in need of replacement, but even if they are bad, I doubt you would get enough fuel past them to flow "fast" either out of OR off the bowl. In other words, you should replace them, especially if they saw a whole bunch of carb cleaner, but I don't think that's where the gross leak is coming from.

For a leak that bad, my money is on the bowl gaskets...

Your question about only leaking under vacuum (when the engine is running) is a good one. :?

The fuel supply between the petcock and the float needles is sealed and will develop a vacuum if you try to pull fuel out of it without venting it. It may airlock (and not leak) unless you've got the petcock open (with vacuum) which will vent the supply through the gas cap and prevent airlock.

On the other hand, the float bowls are always vented to atmosphere and will not develop a vacuum. Because of that, they cannot airlock regardless if the petcock is open or not.

So if the bowls won't airlock, seems like the bowl gaskets would leak with or without the engine running, right? I'm thinking that maybe when the engine is running, it's just shaking the carbs around and what won't leak when sitting still will leak when sloshed? :?:

Maybe just try rocking the bike around violently with the engine off and see what happens? In theory, you should be bone dry even with it tipped sideways until the footpeg hits the ground, right? Don't drop your bike or hurt your back!! 8O

 

Sry. Wanted to add a little more detail that may help pinpoint the problem...

• If the leak is dripping down on top of the bowls from above, it's tubing or fuel supply o-rings. This will leak on PRI and might also leak in ON or RES with the engine either off or on. Depends on if the supply will airlock or not.
• If the leak is seeping out of the seam between the bowl and the carb body, then it's carb bowl gaskets (duh). If your bowl levels are set right and your needle valve is working properly, this will not leak on PRI, ON or RES with the engine off. Might leak in any petcock setting while running because of sloshing.
• If the leak is running backwards out of the carb throat into the air box, then it's a float level issue or needle valve seat o-ring issue. This one will leak in PRI with the engine off.

 

Sounds like in any case the carbs should come off and get a serious inspection and gaskets. I would also look at the throttle shaft seals. More than likely they are hard and not sealing properly.

I just did the seals on my 1100 carbs. They were marginal at best. Looking forward to seeing how it tunes up.
Len has all the gaskets and seals needed so get the parts and do it right the first time and save yourself a major headache.

Then before you put the carbs back on the bike make something to clamp the carbs to and fill them with gas. Do the clear tube float level check and adjust so the levels are right. Its too hard to pull the carbs on and off several times to get those right also. Also helps you double check for leaks at that time also.

MN

 

first thing I am doing in this situation is replacing the float bowl gaskets. Second thing I am looking at is the ability for the needles to return the floats to their set height...if not, soak the upper portion of the needle, not the lower as it is made of rubber. Float bowl gaskets are $4 at last check.

 

so these fuel supply tube orings that chacal sells go around the filter/float needle seat correct?

these parts: HCP2421SET6 Aftermarket Hitachi Buna-N material fuel supply tube O-RINGS, set of 6:

len?

 

I believe fuel supply tube o-rings go on the fuel supply tubes that connect the carburetors.

Needle seat o-rings are a different animal.

 

is this the same as the fuel rail?

what are the throttle shaft v-seals then, and where do they go?

just trying to get an idea what parts i need to get so i can make one big order

 

Rice Burnarr, Are the orings you are talking about only on 550 seca's. O got a 750 and there is no orings on my float seats.

"You're thinking of the wrong o-rings... You don't have to break the rack to get to the o-rings chacal is talking about. He's talking about the o-rings on the float needle valve seat and filter assy. I'm guessing that you're thinking of the ones on the supply tubes between carbs?
The needle valve, seat, filter, and o-ring are at the middle bottom of this pic"

 

Hitachi's don't use an o-ring on the float valve seats (they have a metal or fiber "washer" or gasket under the seat head; the seat screws into the carb body); only the Mikunis use the o-ring to seal the valve to the carb body.

 

word. well, i buttonted the carbs back up to check exactly where the leak was coming from and guess what? NO MORE LEAK!!

However, the bike won't maintain idle off enrichment, so time to start a new thread.

thanks for all the input folks!

 

Haha! Yeah, I've got Mikunis. Don't know much about the Hitachis but I thought they had the same O-ring on the seat. Didn't mean to send you on a wild goose chase... Sorry bout that.

But... The leak is gone? Cool. Hope it stays that way!!

 

Hi Rice Burnaar. I have some questions about repairing a broken float pin arm on my yamaha sx 850. Can you help?
Much appreciated for any advise you can give me.

Thanks Chuck

 

chuck,

This thread is 9 yrs old.....start a new thread with your question....

 

I will save you the trouble, you need another carburetor
I've been working on small engines for 18 years... I've never seen someone successfully repair a float tower.
Sorry

 

Someone here will do better at finding it, but wasn't it on this site I saw a repair with a machined bolt threaded into the carb body to stand in for the float post.

 

Several people on here have done so.

Welding or machining is required, depending on where the break is.

how-i-fixed-my-broken-float-post-mount-tab-ear-pin-thing.17843

http://www.yamaha-triples.org/workshop/ ... Repair.pdf

 

There was a post here about a year ago where a guy welded his post back on and looked like brand new.

 

He had it welded, and other members cautioned that the welder he employed only takes on work occasionally. Anyone who is decent with a TIG and had experience with aluminum should be more than capable of doing the work though.
jim-french-precision-welding-broken-float-post.117989

 

Yes! That was it! Thanks k-moe!

 

Wow! Okay, i guess with enough perserverance and precision, anything can be fixed!
Cool beans, ill keep those repair ideas in mind if i ever need to fix an obsolete carb in the future!