Sounds like a connecting rod knock.
That could spell bad news. [img]/wwwthreads_images/icons/frown.gif[/img]
First of all check your ignition timing...
Can you hear a continuous knock with the engine warmed up and in neutral buy reving the engine at a sustained 2000 RPM? .... sympton of a bad rod.
Or does it knock only under load? ... sympton of detonation (ping]
Next check you spark plugs. If they are pretty white colored it could spell ping (lean mixture)
Also, a stethescope or long screwdriver to your ear with the end placed on the block under the spark plugs will allow you to hear the problem better.
If you rev to 1000/1500 RPM and hear a contiuuous knocking it will probably mean you have a rod bearing or wrist pin going out.