I have same problem on a 1994 hyster with 2.2 gm. The engine make one back fire in intake when we start hot. Just after the back fire, we re-start and engine run good. You can work with it all day. Just make one back fire when start. If you wait about half an hour, it don't make is back fire. We put new cylindrer head gasket, verify head, new wire and spark plug, new vaporisator and lock valve. We try another coil pack, new crank position sensor. I need new idea to resolve problem too :(