Re: 98' 120 hammering/knocking
When you rebuilt the carbs, did you pull the rubber needle valve gasket and replace it and the little ring that holds it in? The reason I ask is that gasohol is causing rubber materials to swell and stick. If you have the old type seats, they could be expanding which does two things, it causes the needle to stick and leans the engine. The knocking noise can be detonation from a lean burning engine.
This is only a theory that I have worked on with some other guys. We figure that at WOT, the fuel pump has enough pressure to overcome the sticking valve and at slower speeds, the engine doesn't need the same amount and the weight and spring of the float overcomes the sticking.
It is only a theory but it has happened to my 85 and seats fixed it. They only cost about $5 each and the clips are $2.50 and are easy to lose.
Hope this helps,
John