I flush toilet and there is a long delay for tank to fill back up...
Is it a plumbing problem or toilet tank problem?

Hi Mdr11726

The problem could be at the shutoff valve, the inlet to the toilet tank fill valve or at the fill valve washer itself.

I would start here by shutting off the water supply to the toilet and then disconnect the water supply tube from the fill valve. If the supply tube is flexible, direct it into a bucket, turn the water on full blast and check for good pressure and flow. If you have a reduced flow then the problem is in the shutoff itself and the shut off valve will need to be disassembled and repaired (or replaced). If you find good water pressure/flow then the problem is up in the fill valve of the toilet. Your best bet here is to simply replace the entire fill valve... only costs about $10.00 at home depot and simply unscrews by one nut. Youtube has tons of videos on replacing the fill valve (fluidmaster fill valve replacement).

Back to you...

Mark