I've been struggling with a rough running engine problem for a long time
now.
It only has this miss / stumble,  when flat out racing, - full throttle, ram
air door open and anything over 2640 RPM.  (the problem seems more RPM
sensitive than throttle and can occur from 19 gal / hr low to 13 gal / hr at
10,000 ft.)  Varying mixture, switching off the mag or electronic ignition
and cycling the boost pump have no effect.
I got serious about this several months ago and started digging.
Valves were a little loose so cylinders came off.  Three had small cracks so
now I have new cylinders.
No change to the roughness.
I also put in new sparkplugs and wires, different hydraulic lifters and fuel
injector nozzles.  I got a new Dukes fuel boost pump and moved it from
forward of the firewall to under the header.
No change to the roughness.
Today, I swapped out the electronic ignition controll to a different unit.
No change to the roughness.
Is it time to overhaul the fuel injector servo?
Any other ideas?

Mark Ravinski
N360KB   1382 and frustrated.