I got a new TT 46 pro and see that there is a small o-ring in a packet with allen wrenches. Does the o-ring go under the nut for the carb. hold down pin? Not sure where that goes. Should I use a sealant when installing the carb? Thanks

There should be two packets of o-rings. The small o-rings are spare needle-valve o-rings. The larger o-ring goes on the base of the carb. You can lube it with silicon grease, or just a bit of glo-fuel.

Sometimes the carb o-ring is already installed, in which case the o-rings in the packet are probably the spare needle-valve rings.

I just recently bought 2 of these engines and the carb O-ring was already installed. Check the exploded parts view sheet, it should show where all the parts go to help you out.