1978 KZ200 engines stalls

I am a new motorcycle rider and KZ owner. My 1978 KZ200 will occasionally stall at stops. I will come to a stop, be sitting in first gear holding the clutch in and the engine will just die.
Most of the time I can start it right up. But twice now, I just can't get the bike started. It only has a kick start. It was rebuilt and has NO electric starter at all. The two times I couldn't get it started, I waited about 15 minutes and tried again and it started up.
The second time this happened a fellow happened along who said he once owned a KZ and his would do the same thing. He listened as I tried to kick start it and said it had compression.
I'm wondering - is it something I'm doing wrong? or is there something mechanically that I could have fixed that would prevent this from happening?
Thanks for advice

Fresh,properly gapped sparkplug? No water in the gas tank? Sparkplug cap on tight?(they usually screw onto the sparkplug wire).I'd suggest dropping the carb float bowl and see if there is any crud there.

Tried running any gas additives? Two good ones are Berryman's B-12 and Seafoam. Both can be bought at Wal-Mart in the automobile oil and chemical section.

You might try turning the idle up too, as this can be one reason why the engine is stalling.

Would also:

(1) assure correct ignition timing, and

(2) check/adjust valve clearance.

Good Fortune!

Thanks. I will check these solutions out.