which 0-ring is best for amal concentrics? - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 7 (permalink) Old 11-16-2012, 12:27 AM Thread Starter
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which 0-ring is best for amal concentrics?

i'm looking to get new o-rings to mount carbs to manifold...i've noticed that some are referred to as "thin" and some "thick"......these carbs are new 930's. is there a benefit of one o-ring over the other? which is correct? thanks, Rick
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post #2 of 7 (permalink) Old 11-16-2012, 03:55 AM
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Use the thin type, 622/101. I have them on my 66 bonneville and they work fine. The thicker type is used on 650 and 750 Bonnevilles after 1970 with shouldered studs, rubber washers and cup washers to insulate and partly flexibly mount the carbs.
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post #3 of 7 (permalink) Old 11-16-2012, 12:57 PM Thread Starter
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thank you!!
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post #4 of 7 (permalink) Old 11-16-2012, 02:25 PM
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Originally Posted by ebsbury View Post
Use the thin type, 622/101. I have them on my 66 bonneville and they work fine. The thicker type is used on 650 and 750 Bonnevilles after 1970 with shouldered studs, rubber washers and cup washers to insulate and partly flexibly mount the carbs.
Thicker ones were definitely used on '69 and '70 Bonnevilles and are recommended for those years. I can't say what would be best on a '66 although I don't think a 930 was stock for that year. Perhaps the inlet manifolds were updated. If so, the thicker ones might be more appropriate.
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post #5 of 7 (permalink) Old 11-16-2012, 05:08 PM Thread Starter
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well, on my 66', the manifolds look to be pretty much stock, but these are brand new 930 Amals, the slides are sometimes a tad bit slow to return to idle, ( i know you have to be careful about over-tightening the bolts) but i just wondered if the thicker o-rings would be more "forgiving" and allow the slides to return smoother....could be partially in the cables too....what's the best way to lube the throttle cables, (i have two separate cables, with adjusters near the throttle at the handlebars) thanks, Rick
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post #6 of 7 (permalink) Old 11-16-2012, 06:24 PM
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The thick O-rings are an improvement,but you need self-locking nuts if you use them.You have to be careful not to over-tighten them and bend the flange.There's normally a gap at least 0.045" between the flanges,with the thick O-ring.

It is all easier if you use the later manifolds.

If the slides are sticking,your flanges may already be bent.
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post #7 of 7 (permalink) Old 11-16-2012, 07:49 PM
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I have found that with the slim export tank and the twin cable twist grip that the carburetters are much more affected by the length and run of the cables which can make the slides slow to shut. But I really like being able to adjust the cables without taking the tank off. I have fixed it the problem for now with stronger springs until I can make some longer cables. I would lubricate your cables and check they are mounted as freely as possible under the tank - and not caught between the tank and the head steadies. You can buy cable lubricators - they are cheap on e-bay or you can use the trad method of creating a funnel out of a plastic bag around the top of the cable and hanging the cable up while oil drains through it. You'll need to tape up the adjusters first!

Triumph used the thicker O ring in conjunction with shouldered studs and rubber washers to rubber mount the carburetter. The reason was to attempt to insulate the carburetters from vibration and reduce fuel frothing at sustained high speeds. The resulting air gap might make the carbs run cooler but you can achieve the same affect with a phenolic spacer with less chance of distorting your flanges.
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