What's that flapper thingy on the choke plate for?

I've been cleaning and reassembling my XR for the last week, an hour or so each night after work, and last night I was cleaning the exterior of the carb before hooking it back up. I noticed the choke plate has a flapper plate-thingy on it. It's a small, half-circle plate on one side of the choke plate only, with a spring. It looks like it allows the movement of air/gas back through the choke plate when it's in the closed position.

What's the purpose of that thing?

I remember reading something once where it could break or fall off, sending metal bits into the cylinder and wreaking much havoc. There was some company that sold a replacement part for this piece that eliminates the potential problem, but which company was it?

Also, I thought I remember somebody saying that instead of buying the aftermarket part, he epoxied the flapper to the choke plate, which also fixes the potential problem.

Is this something I should even worry about? Do I buy the part? Epoxy the flapper?

If I'm going to do something I ought to do it now before I put the carb back on...

It does like you say, releases pressure from a backfire thru the carb when the choke is on. As far as epoxing it, I wouldn't trust the epoxy not to come off and enter the engine. How ironic would that be? I've read of others that have used silicone too.

Baja Designs has the replacement choke plate. It's P/N 151013

https://www.bajadesigns.com/NET/mainframe2.aspx?content=

When I was running the stock carb, I just took the choke plate out,traced it onto a piece of aluminum and took a coping saw to it and made my own for pennies. Just dont use real thick aluminum. Worked perfectly for years. Back in the eighties we had to do this as no one offered this piece.

I think it was XR's only that offers a billet aluminum choke plate for $20. Mine is stock for now.

I bought one of the XRs only and make a couple. I think if you just need one, (I have 4 bikes), just get it from Xrs only. They include new screws. A note about the OEM screws, be careful you don't round them out, they are staked.

I noticed in the Baja Designs link above they only offer choke plate kits for the 400 600 and 650,what about the 250's?Do they have a different design or what?

I thought I got my 400s from XRs only but when I checked their site, seems they're redoing it and can't find anything yet.

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