Way back, I rented a video of a movie about The Flash. With the upcoming movie, I tried to find it, but so far without any luck.
I remember that when I was in the video store, I hesitated between The Punisher with Dolph Lundren (1989) and this one, and as always I went for the lesser known. So it must have come out in the same timeframe.
For the rest, my memories are vague except that
a) he battled a motorcycle gang who threw a kind of molotov cocktails filled with a fluorescent green liquid (rather like the one Herbert West uses to wake the dead)
b) it was awful. In fact, before seeing it, I planned on seeing every live action adaptation of a comic ever made. After seeing it, I decided it would be better to be more selective.
There is a, I think straight to TV, movie called (surprisingly): "The flash". I may have seen it on TV and I vaguely remember not liking it, so that could be a fit. It also has a motorcycle gang, but that could also be in other similar movies...
Here`s the imdb site: http://us.imdb.com/title/tt0099580/
That is the pilot for The Flash TV series starring John Wesley Shipp. It was a pretty good show.
Mark Hamill was the Trickster in a couple of episodes.
That may very well be it. It was a sort of 'origins' story, and as I recall the main character spent forever trying to come to terms with his new power, before anything interesting happened (ie taking on the motorcycle gang).
There was indeed a motorcycle gang in the pilot for the Flash TV series. They were the bad guys for the pilot. They killed the Flash's brother, played by Tim Thomerson. The time frame is correct for the series.
http://www.imdb.com/name/nm0859772/
If you can, track down the first episode with Mark Hamill as the Trickster. It's a fantastic episode and Hamill is clearly having a ball. There was a second episode as well, but it wasn't nearly as good. He brainwashes the Flash to be evil and the Flash's actor is horrible at acting evil.