OHV engine carb adapter/restrictor

I bought an OHV Briggs today. It was sitting for a couple years after it was removed from a tiller. The seller claimed it ran perfect.
I took the carb off to clean it before I tried starting it and noticed it had a plastic adapter/restrictor between the carb and engine.
The carb clearly has a bigger diameter than this restrictor. THe intake hole size looks to match the carb size without the restrictor.
Was this placed in there to limit rpm or power the engine could produce?
Here are some pics of it.

I changed the oil then put it back on with the cleaned carb and the engine started right up and seems to run fine. Why is this there?

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[MENTION=55208]danford1[/MENTION] I don't know the answer to this particular question, but I did attempt to find anything about the YBSXS.2051HF number you asked about.

Not a lot of help, but apparently it's one of the following:

Intek Model 110400 rated at 190 cc. Stroke: 52mm
Intek Model 121400, or 123400, rated at 206 cc. Stroke 56mm Overall height 15.19" from the ground to the tank cap.

Both bores are the same. I'd measure the stroke with a dial indicator and go from there. I've heard these are good little engines to modify, as there are a few parts out there for the 206.
Thanks Dave. It didn't come with a gas tank so I can't measure the height.
I guess I'll just have to pull it apart and get new gaskets.
I'm sure I would catch Hell about re-using a head gasket...
I don't know if I can measure the stroke through the spark plug hole. I can check that later today.

I'll have to research and see what hp each of those model numbers had.
I know there is a Briggs Animal forum on the internet. I'll try asking questions there.
Thanks again for your help.