ParkerVH28 said:
...I have problems what vacuum I have, is lost when RPM is increased. ...plugs are pretty black. When driving the car it has no power.
Thinking the last check is going to be the valve timing.
First, vacuum. By definition, manifold vacuum drops off as the throttle is opened, since manifold vacuum is created by the pressure drop created by the carb butterfly. Think of the engine as a pump, which is "sucking" air past the carb. At an idle, the carb butterfly is a restriction, which creates a pressure drop, so the manifold is at a lower pressure than the surrounding atmosphere (which is a vacuum). As the throttle is opened, the restriction is less, so less vacuum. So that isn't a concern.
Valve timing is almost certainly NOT your problem. The CIH uses a timing chain, which CAN slip a tooth, but I think that is almost an urban legend (unlike rubber cam belts, which are much more prone to stretching and jumping a cog).
A vacuum leak is possible, but you say the plugs are black, which indicates a rich mixture. A vacuum leak creates a lean mixture (everything else equal), and has little effect on power at higher rpm (the amount of air at 4000 rpm is very large with respect to even a sizable vacuum leak). Vacuum leaks cause a poor idle, and poor off-throttle response (when initially reving from an idle).
My vote is either a badly out-of adjustment carb (flooding or too high a float level, wrong jets, or a typical Solex!) , or (drum roll please) a worn cam or out-of adjustment lifters. I hope it is the lifters.
Both require the same initial procedure. Remove the valve cover. Crank the engine over with the ignition wire removed (or ground the high tension lead from the coil, but don't let the engine start or you will get sprayed by oil). With the engine cranking, see if all the valves are being depressed the same amount (about 0.390", or about half an inch). Pay particular attention to the rear valves, as the rear cam lobes are the most prone to wear. If they look OK, heck, even check the valve timing while you are there. Then read the FSM (if you don't have one, get one; no excuses!) for the procedure on lifter adjustment. If you have hydraulic valve lifters (post '70), the procedure is easy. Just rotate the engine to put that cylinder at TDC (Top Dead Center) in the firing position (both valves closed; if you rotate the engine by hand, you can watch the intake valve close, and as the piston comes to TDC, you are set). Then loosen the lifter nut until the lifter is "loose", then tighten until the wiggle goes away. Tighten one more turn. Do the other lifter, rotate the engine to the next TDC (order: 1-3-4-2) and you are done. The solid lifters are adjusted differently, and you need to read the FSM for that. Well, it is similar, but you use a feeler gauge (engine hot) and set the gap between the lifter and valve at spec (0.012" exhaust and intake). The FSM has some bizarre procedure where the engine is running while you set valve lash, but you can start with the engine hot and shut off.
If it is the cam (which is common, and my vote), you need to remove the head, so you need a head gasket set, a new (or good used) cam, and new lifters. More often than not, this is the time to look at other engine work. How IS the engine? Have you checked the compression? Done a wet and dry test? Does it burn oil? Does the chain rattle (new chain and possibly tensioner and guides)? Is the oil pressure good? OK, you get the drift.
Good luck and HTH.