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TOPIC: AT1 Carb Jetting

AT1 Carb Jetting 16 Apr 2019 02:30 #21

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MarkT wrote: I like the early AT/CT carbs because if you're in a pinch... (say you "pinched" and tore the jet setter o-ring...) you can swap the jet setter with the main jet and it will get you by until you can replace the o-ring. Downside is you can't change the main jet without removing the carb anymore.

When they went to the reed valve on the AT/CT in 72 the carb design changed and if the o-ring is bad, there's no fix without a new o-ring.


I went to Home Depot to pick up an O-ring yesterday and everything seems to work! It was a little too late to throw any revs at it, but had a nice smooth idle. (I think it was smooth.. don't have anything to compare it to.) Looking forward to getting back to it after work today. Video attached.

I plan on still purchasing the OEM o-ring, as I just doubt that the o-ring from Home Depot's plumbing section is up for the task of handling gasoline with lasting effect. I WAS however, wondering how close I am to the original specs of the o-ring, if anyone happens to know. The one I bought measured:
O.D.: 5/16"
I.D.: 3/16"

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AT1 Carb Jetting 16 Apr 2019 02:35 #22

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Ah dang. Guess I can't upload video straight here. Will try and figure it out later..

Now, off to make the donuts!

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AT1 Carb Jetting 16 Apr 2019 05:03 #23

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One of the members (Apex?) recommended the Danco #36 3/16" x 5/16" x 1/16" o-ring for the early AT/CT and said it works perfectly. Rubber allegedly holds up fine.

Someone else said the plumbing o-rings are made from Buna-N Nitrile which holds up decent to gas...

Just passing on past info... I haven't verified it myself.

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AT1 Carb Jetting 20 Apr 2019 06:37 #24

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MarkT, that is the exact o-ring I bought, actually. Good to know it holds up.

Here is a link to the bike idling. (hopefully it works) A question though, does everything sound normal to those with more experience? Was wondering about the metal tapping sound? Cause for concern?

photos.app.goo.gl/PV37tBwohPMmh1Sq7

Thanks all

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AT1 Carb Jetting 20 Apr 2019 07:06 #25

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In case anyone is interested, DEET had some nitril O rings he sourced which will hold up if you are stuck with ethanol as well.

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