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SU H6 Carb Rebuild driving me crazy!

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jimitro

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Hi, Just rebuildt my SUs'(kit from J.Curto) and keep getting a gas leak/drips from the bottom of my jets. I've tighen the jet locking nut as far a possible, no luck. Taken apart and double checked assembly, done correctly. Soaked cork washers in oil as recommended. Started the TR4 up, synced carbs, ran great, gas drips again! Could the float level setting, if not correct, have anything to do with this? My previous rebuild kit had rubber washers and had no issues with gas leaks.
I am lost for what to try next. Any suggestions, greatly appreciated!!!!
Cheers
 
jimitro:

If the float level setting is not correct, it could, indeed, cause a leak. Check that carefully.

Another overlooked item is the overflow pipe from the float chamber. Sometimes they become clogged, especially if you hav soaked them in cleaner while rebuilding the carbs. Be sure the opening to the pipe and the pipe itself are clear -- blow air through it. If the pipe is clogged, pressure builds up and gas can leak from the jet assembly.

I don't think your problem is with the cork washers, as long as they were not broken when putting them on (you soaked them, so OK).
 
Readjusted the float level and checked to insure all air holes were open, still leaking. Could it be that maybe the cork washer on the sealing ring in over compressed/tighted?
May have to go back and replace the cork washers with my previous rubber washers and see what happens.
 
Just a thought, I have seen jets where the jet itself would leak.

Otherwise, if it is coming out the bottom of the jet assembly, then it has to be that lower cork seal that is leaking. You could try assembling without the spring on the mixture nut, so you could wipe the outside of the jet housing to determine whether it is coming through the housing or running down over the outside.

If it's on the outside, then that big cork gasket is the problem. But it shouldn't be possible to overtighten it. The nut should tighten against the lower jet bearing (through a copper washer), which presses against the upper jet bearing, which has a copper washer between it and the carb body. The cork compresses only until the jet bearing halves are locked firmly in place. If the aluminum ring under the cork is coming up against the carb body, then one of the copper washers may be missing (or too thin).
 
Always worth another look:

When putting the jet through the base of the carrier assembly, did you put a small, oiled cork on the jet, after passing it through the carrier, and then a washer with the concave side toward the seal? Then the jet spring. Then the next small washer with concave side upwards, and then the second small oiled seal on top of the small concave washer? That arrangement should work and not give you a leaking problem.

Also, if you are reusing your old upper jet bearing, be sure you have removed the old cork or rubber washer that sometimes gets stuck in it and is not very visible. If it remains in there, and you put another cork washer into it, it might very well leak.

The lower cork seal nowadays is a bit thick, and as you tighten the jet locking nut, you sometimes have to use a small screwdriver to push the cork washer into the retaining aluminum collar so it fits. Once the jet has been centered, the jet locking nut should be well tightened. Making it tight shouldn't cause any leaking.



If the problem isn't there, then I don't know what else to suggest.
 
Ed, Thanks for advice on the leak, will triple check the rebuild again. I think I may have figured out the cause after much research on the net. When I assembled the carbs, I may not have let the cork washers soak in the oil long enough. I only soaked them for about 10 minutes. There was no time recommendation to soak in the instuctions, manuals, anywhere I looked until a SU website suggested an overnight soak to insure the washers are ready prior to assembly. Will update on Weds as if worked or not. Hope it was that simple!
 
Good luck, Jim. But since I have never soaked mine, I rather doubt that is the problem.

Certainly could have been a bad cork ring, though. Cork is a natural product, and voids are a definite possibility.
 
Jim,

I don't think the soaking time is the problem. Some people, as you see, don't soak them. Some soak them in water(!) The SU DVD instructions call for about an hour. The SU instructions that come with the kits recommend overnight. You just need to make them a little pliable.

A real possibility is that the large cork washer on the aluminum collar may have been "crimped" a little. i.e. an edge may have extended out over the edge of the washer. If that is the case, a leak is possible (though not inevitable). That's where the careful use of flat screwdriver to gently push the cork into place will help.

Do check those small corks, the two concave washers that separate them from the jet spring, and the large cork and aluminum collar. It seems to me that the problem should be in that area, if the leak is, indeed, coming down through the jet.

Here's another possibility from another source: "The large rubber seals that seal the float chamber feed to the carb where it attaches to the throttle body can leak if overtightened or the little steps are folded over. Looks like a leak from the jets. Take them off and reset the seals, then tightend the bolts with gas in the bowls until the leaking has stopped."

Also... be sure your float valve needle and valve assembly are clear of debris. If it is clogged, for some reason, you can get a leak out the jet. Make sure the valve outlet is clear.

By the way, have you installed an electric fuel pump? If you have, it's possible that it is creating too much pressure and causing the leak. Just a thought...
 
Ed,
Success on my carb leak!! Thanks to your suggestions I looked closer at my jet assembly one more time and found an old gasket was still stuck inside.
I cannot believe I missed it! Guess this is what happens when you don't have good lighting in your garage. Gotta blame it on something instead of me being
a dumb...! Or maybe it was the lack of Beer that I gave up for Lent!!!
No more rebuilds until Easter!
Thanks again
Cheers
 
Jim,

I've been told that overlooking the old gasket is a "common mistake." I'm glad your problem has been fixed.

And now to some serious, leak-free, driving.

Cheers...
 
Congratulations on finding the leak. I "rebuilt" mine using all old parts and "O" rings from the local hardware store, no leaks. I can't remember if I used the cupped washers or not, I suspect yes, works fine ( 2yrs .)

TR-3B
 
Doug,

My only question about using "o" rings from the local hardware store is, aren't they susceptible to deterioration from alcohol in modern ethanol gasoline?

Since you have had no leaks in two years, they seem to be working. Perhaps the "o" rings you purchased are ethanol-resistant rings.

Just a thought...
 
LexTR3 said:
My only question about using "o" rings from the local hardware store is, aren't they susceptible to deterioration from alcohol in modern ethanol gasoline?
Click to expand...

Not likely. The most common O-ring material at the hardware store is Buna-N (also known as NBR or nitrile rubber), which will stand up to both ethanol and gasoline.

The problem is that sometimes the store doesn't know what they are selling and they sometimes have EPDM, which will not stand up to gasoline. (It's fine with ethanol, just not petroleum, go figure.)

Another problem is that NBR doesn't like high temperatures. It's normally only rated for use to around 225F; but normally your carb jets shouldn't get that hot (as the gasoline will boil in the jets if they do).

If it worries you, look for HNBR O-rings. (Likely not available at your hardware store, but readily avaialable at places like MMC

Of course it might be easier to just order from Moss :smile:
 
Hi, Randall,

I was just curious. I haven't had occasion to use 0-rings yet because I've been quite satisfied with the cork seals. I do have some 0-rings, but I got them not from my local hardware store but from Moss.

I get the feeling from what I have been reading on this forum that the proper o-rings will outlast the cork seals, but, as I said, I haven't had any complaints with the cork seals yet.
 
I ran cork seals for a lot of years. They work OK, but only lasted a year or two for me. I got pretty good at changing them without pulling the carbs, but it was still annoying. So I bought a pair of O-rings from Moss, which were still sealing fine after more than 5 years. They did show some wear though, so I replaced them when I moved those carbs to my current TR3.

But I drive the car almost every day, sometimes using the choke as much as 3 times each day. For your usage, I'm guessing the cork seals will work fine for many years.
 
Randall,

Sounds good to me. I drive about once every ten or twelve days. Not much use of the choke.
 
Hey sorry that I'm digging up this older thread but after reading it I'm curious if any one knows the size o-ring that would work for this seal?
 
Hi, Eric,

This O-ring measures about 3/8" across. It is Moss part #365-420.
 
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