450 problem staying running

Sounds like a choke issue. but I am no expert on Bikes.

the automatic choke is working and thats why it does that because the car hasn't been cranked and its cold natured. this is normal for older cars and trucks with regular carbs.

the wiring or components are worn causing resistence--getta repair manual for the detailed tests----------also when at home run an electric fan at motor when stopped--it cools it fast and gives air cooled engines 3 times the life span

Two thinks i can think of are cleaning the spark plug. and/or adjusting the idle screw on the side of the carburator untill the engine sounds normal.

Run some carburetor cleaner through the system to remove any dirt which may be interfering with the carb diapharms............Let idle for 15 to 20 min before trying acceleration.........Hope this helps you out.

first drain the carby, then set your air mixture screw 2 turns out, from the fully turned in position. The starting proceedure is as follows, when the engine is COLD, turn on fuel, pull on the choke fully, and kick the engine over. DO NOT use any throttle, when the engine is cold, and the choke is on. Remember Choke on, NO throttle.
When warm, no choke, and a little throttle when kicking.

Check your spark plug. If it is not all black, it should be ok. If it is, replace it. Reinstall new plug, Kick it full choke no throttle. Let it run for 15 secs with the choke on. Shut the choke off while reving it. If the bike will not idle, clean the carb. Chaz Moto DC

The choke should only be used when starting cold. After the bike is warmed up you can turn the choke off. If it keeps shutting off after being warmed up for a few minutes, then check your gas/air ratio for the idle air mixture knob. Loosen it up 1/4 turn to allow more gas to flow.

I have a crf 250 R and i have learned multiple things about these bikes like if you leave it running and not riding it for about ten min. it will over heat. they love race gas 113 octane,and alot more. but your prob sounds strange. i know if you hold the hot start while its runing it pops that could be a problem. or it could be you are not cleaning the bike out i would need to know more about this to give a definate answer but try going over the bike. Look at key parts like the
carb
air cleaner
fuel line
any thing that is nesessary for the bike to run.

you need to check your choke prob not a choike issue just you have it open or its stuck but it sounds like a easy fix