Carb float bowl: what exactly is the purpose of this o ring?

[mikerophone]

I've dipped and sonic cleaned 5 sets of GS BS32's now (2 each 750 and 850 and now a 550) and although they all have the circular impression, only one set had this o ring on the from edge of the float bowl:



Robert Barr's kits don't come with them and I honestly don't see the purpose of the ring or the semi circular "hump" in the gasket above that.

Anyone care to enlighten me?

[cowboyup3371]

I don't have that O-ring on any of my carbs while the bowl gasket is designed with the same hump on it. I don't believe there's an actual purpose just the way they designed it.

[Crankthat]

Learned this info from another thread a few years back.

The depression the o-ring sets into is actually a plug.
Someone mentioned the plug fills a hole vital to the manufacturing process of the carb body.
The original thread this info was garnished from was started by a member who had a plug fall out.

The o-ring in place for possible fuel passing the plug.

This is the thread.

http://www.thegsresources.com/_forum/showthread.php?222851-GS850-Carb-Mystery-Hole&highlight=hole+carb

His picture link.

http://imgur.com/a/O17VG

[JTGS850GL]

I've seen some with and some without the "O-ring". The stock spacer part is actually a round O-ring but flat on the top and bottom with squared off edges. It keeps the metal plug in place. The ones that didn't have it seem to have the metal plug higher up. No room for the spacer and no room for the plug to move. If there's room for the spacer then use it.

[Nessism]

The O-ring is a supplemental seal of sorts. Some carbs came with a seal and others didn't. If the plug is sitting down some I'd use the O-rings. Can't hurt.

[chuck hahn]

As was mentioned above.....its purpose is to hold the plug in place snuggly. And secondarily, as Ed mentioned, it supplies a base for the actual gasket to rest on so it doesnt tear right above the plug.

Its typical to CV carbs only. No VMs I have ever worked on has them.

[mikerophone]

Awesome - thanks for the replies and explanation. Makes sense, perhaps I'll try and source 20 of these from the local o ring supply house just in case.

[JTGS850GL]

You shouldn't need that many. They don't normally go bad and usually last for 30+ years before needing replacement.

[Steve]

Also keep in mind that they don't seal anything, they just provide a little bit of "push" to keep the plug in place.

Thickness is more important than overall diameter.

.

[mikerophone]

Thanks guys - JT, I have 5 racks of carbs so 20 would be for all 5, they are cheap locally. Good thinking on the thickness Steve, as long it's close, I'll go with a smaller width if that's all they have.