Same thing happened to my daughters 90 Accord. Turned out to be a burned exhaust valve on #3 cylinder.
A compression check confirm it.
When I pulled the exhaust manifold, I could actually see it. I rotated the crank until the No. 3 exhaust valves closed. I used a small inspection mirror and saw a suspect area, then confirmed by inserting a small wire through the hole. Wasn't very big...guess it doesn't take much.
