I have a 1972 honda cb750 that I have modified with 1978 cb750 carbs. I am having a problem diagnosing my problem. Here is what I have done. Adjusted the valves, cleaned and synched the carbs, installed new jets 105, 110, 115 same thing happened, Measured the compression cold got 125 psi on all cylinders, added oil got 180 psi on all cylinders. Checked them when hot got 125 on 1 and 2, got 90 on 2 and 3, added oil got 110 on 1 and 2 and got 80 on 3 and 4. I may have done the hot test wrong, not sure I am going to do it again. replaced coils, new battery, adjusted points. Engine is leaking a small amount of oil from the head gasket. Exhaust headers may need some tightening due to poorly threaded holes in block. This is what happens - Bike starts every time with no issue, idles great, revs well, sounds good, no obvious smoke. When you take it for a ride it will run well at low rpms, but when you get to 3/4 and full the bike stays flat and sputters and jerks until you turn the throttle bad to under 3/4. If you do a spark plug chop at the problem speed 3 and 4 plugs are black sooty a bit wet, and 1 and 2 look light tan and overall good. What is going on. Is is valves, rings, head gasket cam chain, or carb issue. I am really getting tired of trying things out here. Almost ready to buy a new engine and start over. Any advise would be greatly appreciated. Thanks
