My 1978 125 will kick off some time and run for a min then die

Sounds like you got some bad gas. May need to replace the fuel filter

sounds like a fuel filter issue is there an inline filter

Sounds like the gas tank isn't venting.

If air isn't allowed to enter the gas tank to replace the gas flowing out, vapor lock happens.

Next time it dies, remove gas cap and see if it starts quicker/easier, and runs longer.

If so, then you have a plugged vent.

Tune up,plugs wires,coils.crankshaft sensor.

running out of time and too rich
suggest that you call in an auto gas technician to check and adjust the regulator /converter for the gas to get it running right

Any possibility there's a problem with an obstructed vent?

I used to own an old 250 Ducati and I had a similar problem but all it turned out to be was not shutting off the gas **** whenever i shut off the engine even for a 10 min stop.After I resolved that problem the little F....r ran great.I do not know if this is of help or not but that was my resolution.It also did not cost me an arm and a leg...Just an arm to find out

There are two things to check for. One, vaccum might be created in the tank only allowing the unit to run a few minutes. If it starts to die after running a few minutes, removing the gas cap. If it keeps running, you need a new gas cap. Otherwise your problem is in the carb. It could be bad gas that was in there before or you have debris in the carb itself which only allows the unit to run on choke. Make sure if you have a fuel shutoff valve that it is on.

i would try first change gas make sure its a mix of gas and 2 cycle engine oil,second new spark plug third make sure theres nothning in the gas line hope this helps

Try changing the fuel filter. You may want to consider a Weber carburetor conversion. That Asian carb is old