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SU carb rebuild jet corks and washers

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jsneddon

jsneddon

Jedi Knight
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I'm rebuilding my SU's on my TR3 and the gasket kit I got from Moss came with cork gaskets for above and below the spring that the jet goes through. #92 on this picture:

https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29127

I see that they sell cork or rubber o-rings. I rebuilt them in 1990 and the kit came with the rubber ones so I used them... but when I took them apart the rubber was all falling apart.

I'm using the cork this time (because that is what I have handy) but I'm wondering if the reason for the rubber being all funky looking was because I put the cupped washer on the wrong way.

The question is... is the concave part supposed to point toward the spring or the cork / o-ring ???? The pictures don't show enough detail in any illustration I can find in the 4 different versions of shop manuals I have.

As I looked at it over and over again I convinced myself one way and then the other... the cup part seems to be a nice fit to the smaller diameter at the end of the spring and pushes the cork nice and flat. Or the cup part seems to form the cork nicely and then the flat side has nice even pressure coming from the spring.

How they came out is irrelevant since I'm the one who rebuilt it last time and I did it with the cup toward the O-ring but the cup seemed to cut out part of the rubber when it got compressed.

grrrrrrrr. /ubbthreads/images/graemlins/confused.gif

Anyone know for sure which way they should go?

And is anyone happy with the o-rings? I'm kind of leaning towards the cork at this point judging the condition of the rubber that I pulled out.
 
Mark I have a highly detailed exploded view photo of a typical SU carburetor that clearly shows that the seal should fit in the cup. In other words, the cup side should face away from the spring.

I'll scan the picture and post it shortly.

BTW... I went with the rubber 0-rings, but I'm about to pull the carbs off and go back to cork. This is the first time I've ever used the rubber 0-rings, and one is already leaking! I've used cork in the past and never had any problems.
 
Attached is a blow up of the illustration I have showing the jet seal orientation.
 

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  • 102269-SUjetseals.jpg
    102269-SUjetseals.jpg
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Thanks - I get it now... of course the corks from Moss look nothing like these but what the heck. They look more like a couple of cork soda straws. But they aren't leaking yet and they seem to fit much better than the o-rings did.
 
Thanks for the post Jim I was wondering about the cork and rubber also. Moss claim that the rubber never leaks, but I have always had trouble with both of them leaking. I figured the leak was just part of the engineering of the choke assembly. In addition to that I figured it was because I bought the replacement parts instead of the S.U kits. The parts that I wonder about are the little copper washers in the assembly. Are they shims? Do they provide some of the sealing? Anyways, I have just come to live with a little bit of a leak.

George
 
Jim, the cork does seem to seal better but I always have trouble with the choke being hard to come off until they get a bit of ware on them, so keep a check on it, don't want to burn a valve. Wayne
 
I believe that the copper washers are more shim-like than for sealing. I foud this information about them on the web
at https://www.jcna.com/library/tech/tech0006.html#authorauthor

"On the H series carbs the upper jet bearing copper washer is supposed to be 0.016" thick. Many after market kits have this washer 0.025" or even 0.033" thick. This holds the complete jet assembly down farther away from the needle than intended and defeats about 1/2 turn of the mixture adjustment nut (ability to lean out). "

I also soaked the cork in oil before installing it to make it more pliable and hopefully this will keep them from sticking as mentioned above.
 
I always soak the cork in water first (for 10 minutes or so) before installing.

After thinking about it, I doubt the orientation of the "cup" washers really has much effect on the seal. I suspect the main purpose is to provide a uniform bearing surface between the spring and the seal.

I will say that with the rubber seals in place that I've noticed that the "choke" action is much smoother than with the cork seals I was using.
 
Having the concave face of the washers twards the cork will force the cork to squeeze in twards the jet (it's basicly an inclined plane)giving a better seal.that's the theory.
I've always soaked all the jet parts, including the cork gaskets with WD40 prior to assembly.
Don't try to use PB Blaster. It has the same effect on the cork as it does on the styrofoam cup. Your eyes will grow larger as the gaskets dissappear before you. /ubbthreads/images/graemlins/eek.gif HaHa
 
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