Starts but dies after several seconds

Sounds like a gas issue, or lack of gas? Is the first time you're starting it for the year? Could be a plugged carburetor or junk in the bowl of the carburetor. I'd probably start there as you must have spark since it does start.

That could be water in the fuel tank, dirty fuel injectors, or a dirty fuel filter, just for a start.

carburetor needs cleaning and rebuilding

Check the fuel pressure with a gauge. The pump may be going bad

If you bought it used, you can bet that they didn't run it out of fuel before they stored it, so the gas evapoated out of the carb and all that was left was oil, so mix your fuel 8 to one eight parts gas and one part oil, you'll have to hit the primer botton several times.

The security has been activated. you have to turn the ignition on, but don't try to start it, let it set for ten minutes turn it off without pulling the key out and try to startit. you may have to do this three times on ten off, on ten off, on ten off, then try to start it.
Good luck Randy

Well after you clean it out and get it running make sure you dump some sta-bil into the gas tank next time it is going to sit idle for over 3 months. the gas turns into a shellac which glues up the carburetor.

your automatic choke is defalting

hmmm, a few posibilities, might well be split cab diaphragms but overhaul should have spotted that. sounds like either too much gas or not enough, either flooding/gassing up or fuel starvation. could try running it without the aire filter too see what happens. it should run weak so if bike is better then you have too much gas, if bike worse then runnig weak to start with. I have seen this before with one particular cause.... petrol tap was leaking, gas runs past pistons when bike not running, soaks past and into crankcases. as breather recycles vapour back in to air box, when bike warm it's as rich sas hell. take of oil filler cap on engine and have a good sniff. you should smell only oil, if it's a strong smell of petrol, change oil and filter, dump petrol tap or see if new seals available.

check the pressure replace valve or a bypass valve