WR400 popping and sputtering help please

Just bought the bike a few weeks ago 99 wr400 and have not really changed or modded anything. It has ran pretty good up till a couple days ago. Starts fairly easy and runs pretty good with the choke on. When I push in the choke it sputters and pops and dies. I haven't rode the bike but a few trips up the street and back. The only thing I have done is add a brake light and switch. I cant really say what size any of the jets or anything are but I hope someone may be able to point me in a direction to start looking. Like I said before, it seemed to run ok until a few days ago. Kinda all of a sudden is running like crap.

Inspect the fuel screw, ensure the spring, washer and oring are there and serviceable. Check the screw tip, make sure it is undamaged.

Remove the cap on the bottom of the carb, confirm no debris

Install a BRAND NEW pilot jet

Fine adjust the fuel screw for a perfect idle with a hot engine (after a fifteen minute ride, not a rev up in the garage).

I found out that my fuel screw o-ring is GONE! Time for an upgrade I guess.

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