Got it brand new in the mail the other day.

Question #1: How do I install the carb so I can compress the O ring? Do I just push down as hard as I can and tighten the compression screw and nut at the same time? I'm concerned that it will leak air. The compression fitting doesn't pull the carb down onto the O ring.

Question #2 Do I put thread lock on the compression screw and nut?

Push down hard while tightening and do not use any thread lock.

Enjoy,

Jim

As w8ye said.
Sometimes the carbs are a little tight (Too much precision :-') and
I put a little oil on male portion, stick it in the engine portion and work
it around a little until it is halfway free. This helps to assure I have the
carb seated when I tighten it up. Make sure you get the cinch bolt good
and tight also or after several flight they will work loose. Another little
thing I do is to clean all the oil etc off the top of the carb and put a dab
of expoxy over the little throttle barrel screw on top. I have had a couple
of these come out over a period of time and this seems to prevent it.
Your gonna love that engine

On the barrel retaining screw I have used blue thread locker had the same problem with the
screw departing. the irvine jetstream carbs are great have 4 53s 1 46 and 2 irvine 40 diesels
never a carb problem (the 46 and 53s are all diesel conversions)