Warms up then dies

Have 1980 kz750 it warms up bought 10 15min then dies on me... New coil packs rebuilt engine valve job runs good no misfire or backfire or hesitation... I don't get what it could be... Any insight

Have you checked the spark when it dies you said new coils what about the rest of the ignition and could also be not getting fuel

Did notice one thing won't start off choke would that have anything to do with it

What do the plugs look like?

Brownish

Will it keep running if you give it some gas?

I'll have to try that I only let it idle yesterday I never can catch it cause it don't die slow it dies fast

Then it take few turn over to start again

The jets under the plugs do what operation

You've been chasing similar problems in other threads often jumping all over the place. An engine only needs 3 things to run:
1) Fuel
2) Spark
3) Compression / Air

I highly doubt you're missing number 3 since it does start cold. I mean you could have a valve clearance issue that only presents on a warm engine keeping them from closing all the way but I'd expect that after repeated tries to start the bike you would be getting some backfiring out the intake or exhaust or other signs of that.

Since it idles for a bit then dies hard and doesn't restart you've got to be missing #1 or #2, spark is the easiest to check (in my opinion) so I'd start there. Check spark when it's cold and again when it has died and won't restart. Hopefully you have a good strong spark in both cases. If so, move on to fuel. Since it runs for a while then dies I wonder if your float level is getting out of wack? I don't know what carbs are on your bike but if you can check the float level on the bike check it when you know the bike will start and when the bike has died and won't restart, see if it's the same. SInce the plugs are brown but not wet with fuel I wonder if the bowls are running dry?

For sure that's why been jumping around thing drive in me crazy cause get one thing going then something else comes up.. Mean never had this much confusion with a engine I've had four wheelers and snowmobiles that bought that had knock and they still run

Let me ask cause gonna take for a ride later at what voltage will the coils have weak spark or no spark voltage output wise to the rectifier cause gonna ride with the meter so I can rule out no spark problem