engine won't start/headlight is off

My bike is a 1981 xj 750 seca with about 20,000 miles. Most of the time it starts immediately but sometimes it fires and quits. I crank and crank and sometimes can't get the engine to start for a long time. I've noticed that when I crank and the engine won't start the headlight is not on. Then when I crank and the engine finally fires the headlight is on. Anybody know what's wrong?

 

There's a Relay that opens the Headlamp Circuit during cranking so the Headlight won't draw current away from the Starter Motor.
That's designed in. Normal.

That the Bike won't start right away is either Fuel or Ignition.
90% of the time ... it's the Carbs.
Sometimes it's the Fuse Panel.
Aging components.

First you test for Spark.
That will be Yes or No.
Yes?
Fuel Delivery issues.

Carbs that haven't been pulled and thoroughly cleaned head to toe are usually to blame for Duel Delivery issues.

Whens the last time you KNOW, without a doubt, that the Carbs were Cleaned, Diaphragm Pistons Bores resurfaced, Clunk Tested, Bench Synced, Float Heights confirmed, put on the Bike, Vacuum Synced and had the Pilot Mixtures set for optimum performance?