Beach-goers beware: subway service will be spotty in Coney Island on Saturday. A fire broke out on the roof of a signal room near the West 8th Street station on Friday evening, shutting down service on the F and Q lines. MTA spokeswoman Deirdre Parker said the fire was out by 9 p.m.— but it was too late for repair workers to get up on the elevated tracks. Workers are set to start repairs at daybreak Saturday, but it's unclear when service will be restored. The F isn't going past Avenue X and the Q terminates at Brighton Beach. Shuttle buses are running and the N and D lines at the nearby Stillwell Avenue stop were not affected. There was no immediate word on what caused the fire.