Rheem gas furnace false starts

[Buzz]

I have a rheem highboy gas furnace (1987 manufactured) that is having false start issues. Burner will come on for a second or two and then stop. A few seconds later it will repeat. It does this three or four tines before the burner stays on and after a short time blower kicks in. I'm worried that one time it will not start

Any thoughts on the possible cause and fix?

Thanks

Brian

Furnace model is RGAC-08KA

[Porcupinepuffer]

Dirty flame sensor or crossover tubes at burner ends are not carrying gas across fast enough to reach flame sensor. I'd start with cleaning flame sensor with emery cloth.