my car won't start when warm

[civicdj]

i bought a '90 accord, and it runs great, and starts fine.three weeks later, different story. in the morning it starts great everytime, i mean everytme. but if i were to go somewhere and and get back to my car in five-ten minutes, it doesn't start, and then i wait 5 minutes, and it starts fine. so there is a gray area, of when i turn the car off(after it's already warm)to about 20 min after that it won't start. it will try but nothing.

when idling, sometimes it is a little low, say 600.