Hello naj,
The injectors are positioned in the intake port in the cylinder head, above the intake valve. They will not be an indicator like a spark plug. In addition I have never seen them be the source of a high speed misfire. A ignition coil can misfire at high rpms and be perfectly fine when cold or at lower rpms. Spark plugs that are new but have been run too lean or rich can also cause high rpm problems. The ignition wires and the resistor ends themselves should be checked with an ohm meter. Make sure the distributor rotor is correct some are close but wobble and do not fit correctly. Check the distributor advance springs by twisting the rotor, it should move clockwise then spring back. The engine must have the correct fuel pressure to run especially at high rpms when the demand is greatest. Bad ignition condensors are hard to diagnose but fairly inexpensive to replace. Try the cheap fixes first.
Check your valve adjustment and valve timing. If too tight, maybe some escaping exhaust gases are the cause of this carbon on the injectors?
Good Luck!
Joe Alexander
Blacklick, Ohio
