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TR2/3/3A Carb Leak

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frankfast

Jedi Trainee
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Can't seem to keep the bottoms of my carbs dry. They leak around the jet head and not at the large gland nut. I've taken them apart numerous times and replaced the small o-rings(non cork) around the jets but to no avail. They were actually dripping but now just wet. The mixture nut was screwed out 2 1/2 turns per manual. Any thoughts?
 
The mixture nut should not matter. Consider 1. The springs putting pressure on the "o" rings, 2. The shape and orientation of the cups putting pressure on the rings, & 3. Smooth without scratches on jets. Sure that the rings are of the proper size, (try new rings?).

Le T.
 
The cups are new as are the replacement o-rings from Moss. It's possible that there is not enough pressure on the o-rings because the spring is weak. The gland nut squeezes the assembly together putting pressure on the o-rings via the spring. Maybe there is a spacing problem.
 
That's what I figured but it seems that when you tighten it the slide starts sticking. That means the needle is not centralized. It's tricky. I tightened it and did get better results. Before it was dripping and now just wet. Does the cork have to swell before it seals? I'll run it for awhile and see if it dries up.
 
Snowkilts said:
Tom Bryant sells a little kit for eight bucks with rubber gland nut o-rings and viton jet o-rings (4 per jet). I have them on mine. They work well. https://thosbryant.wordpress.com/category/su-carburetors/
Click to expand...

Actually, those jet o-rings are Teflon. Viton doesn't work well because the jets will not slide easily.

For anyone looking for a large quantity of these Teflon O-rings, here's where I've been getting them lately:
https://www.theoringstore.com/index.php?main_page=product_info&cPath=367_93_96&products_id=4168
There are numerous other sources for them.

As for the rubber o-rings for the gland nuts, they're just common hardware store variety nitrile (Buna-N), 3/4" ID by 1" OD. Except that your hardware store probably stocks 90 durometer, whereas I recommend 70 durometer since they're a bit easier to squeeze into place.
https://www.theoringstore.com/index.php?main_page=product_info&cPath=367_23_25&products_id=1179

The O-ring Store also sells 50 durometer, which would probably be even better, although I've never tried them:
https://www.theoringstore.com/index.php?main_page=product_info&cPath=367_16_18&products_id=870

Tom Bryant
 
Last edited:
Tom Bryant said:
Actually, those jet o-rings are Teflon. Viton doesn't work well because the jets will not slide easily.

Tom Bryant
Click to expand...

I stand corrected. They work great though.

Also thanks for all the info on your blog Tom. I used it to go through my SUs this past winter and fix all the things I did wrong when I rebuilt them the first time. They work much better now!
 
Took it apart yet again and thought I had it solved as it idled in my driveway. Everything was dry. Then I took it for a short drive and when I came back checked it again. It was wet, not dripping, but wet. I've decided that the culprit must be the jet itself. I'm going to replace the whole jet assembly.
 
Have you cleaned out your float chambers recently? Checked that the floats aren't cracked and filling up with gas? The needle valve is in good shape and not fouled? Float lever adjusted correctly? If anything is not working right it could be trying to push too much fuel into the jet, which has to go somewhere.
 
frankfast said:
Took it apart yet again and thought I had it solved as it idled in my driveway. Everything was dry. Then I took it for a short drive and when I came back checked it again. It was wet, not dripping, but wet. I've decided that the culprit must be the jet itself. I'm going to replace the whole jet assembly.
Click to expand...

There's probably no need to replace the jet. Assuming the sides of the jet are smooth (which they almost always are), the only other way the jet itself might be the source of the leak is if the screw that holds the yoke on the bottom is loose and leaking. If it's loose, then you can easily seal it up with Loctite.

The far more likely source of your leak is the lower cork jet seal. And if that is not the source, the next most likely thing would be a loose upper jet bearing. There is a copper washer up there that can leak if the jet bearing retainer nut isn't sufficiently tightened. My money is on your cork jet seal.

Tom Bryant
 
I've discovered my problem and it is embarrassing. The cups and o-rings are reversed. The spring is bearing on the o-ring instead of the cup. I realized the mistake when looking at the exploded view. Common sense dictates that the spring would bear on a hard surface and not an o-ring. I need to go back to common sense school. Will fix it tomorrow.
 
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