The car runs fine until I get it up to 4000-4500 rpm for more than a couple seconds. Then it acts like the motor dies (problem is worse when the engine has some load like going up hill). If I let up on the gas it recovers briefly. *OR* if I floor it then the engine picks up again (somewhat weakly). 90% throttle runs roughly, 100% is smooth but not as powerful as it should be.
Its that full-throttle thing that I don't get. If it was fuel starvation, shouldn't it happen worse with more throttle?
I adjusted the main mixture screw a while ago too far rich and the plugs were black. I adjusted it leaner a couple days ago thinking that was the problem. Yesterday I replaced the plugs with new ones and the old plugs had returned to white with brown deposits. But I had the same problem driving on the new plugs. All the plugs are consistent in color.
Any ideas of where to look?