[gumba]

Short background, 3.4 twin plug, 9.5 comp, 50 pmo's, Electromotive hpv-1 crankfire, 1 3/4" o.d. European Headers, custom muffler incorporating the cookie cutter straight pipes. Was running Bosch ws3, switched to NGK 7iex. Motor build by J.W. and raced in NorCal, moved to Santa Fe, NM (7,000 ft.) now a street car.

The problem is the plugs are black and the motor starts missing after about 1/2 hr. drive. I switched from the Bosch to the NGK's, and dropped from 60 idle to 55 idle. No difference. The other issue is the carbs don't respond to the idle screw adjustment either with the 55 or 60 idle jets. I have swapped out everything on the ignition side, crank sensor, coil packs, checked the wires, different plugs. I run dual a/f gauges showing around 13:1 idle, 12-12.5:1 under acceleration.

I run a tamer version in my bus with no issues. Stock 3.2, 46 pmo's, Electromotive hpv-1, SSI's, and sport muffler. That motor actually shows running richer than the 3.4.

Any old school high altitude mechanics around. Any suggestions?