Where is the oil filter on a 1995 Honda Nighthawk 250.

To change your oil you will need 4 quarts of oil, a filter, and a new aluminum drain plug washer. You can reuse the old one if it has not been squished out of shape. Your motorcycle comes from Honda usually with 10w-40 mineral base motorcycle oil.

try slackening the valve gaps , did you clean the valves and re lap them in with paste , you got a spark , check compressions , fuel good and timing correct ?

On the gearshifter side of the bike, in front of the rear turn signal is a lock and loop thingy. That is for locking the helmet. But, if you turn the key as though you are going to lock the helmet, and push a lever next to it, the seat will unlock. I believe you move the lever towards the front of the bike. The key will stay in the lock when you are in this mode. Give the seat a pull on the passenger strap. The seat will pop off. Put back on by looking under the seat when reinstalling it. You'll put it back on by putting the drivers end of the seat first, then the passenger part.

It needs four stroke motorcycle engine oil, dont use car engine oil it has friction modifiers that will cause clutch slip.
20w40 is fairly standard for most *** bikes
Go to a bike shop and they can advise and will have oil filters,

It often helps to bleed the brake fluid, and clutch if it has a hydraulic activated clutch.
There may also be a couple of grease nipples on the rear suspension

I have had my 2008 Nighthawk 250 up to 70mph with some left over. I just got it so I haven't really run it full throttle yet ( 75 miles on the OD ) I weight 300 lbs. I would guess 80 on a flat road. I felt comfy at 70 but this is my 5th bike. I bought this one for the gas mileage and 1 yr. warranty. I will try actual top speed on the Interstate in about 1000 miles. Hope this helps. I like the bike. Chris