My '84 Westy 1.9 runs great--most of the time. Full power, like 70+ mph even
going up long inclines. Had it to 82 on I5 yesterday, drove excellent.

However, and ESPECIALLY AFTER GOING DOWN LONG HILLS, she loses power to the
point where, even going downhill, she won't accelerate. For some reason,
COMPRESSION BRAKING seems to throw something out of whack.

Is this a clue? Or a red herring? If it's a real clue, where would you look?

Ken Lewis' O2 sensor monitor shows the engine running extremely lean (low
voltage from O2 sensor) when she's out of power. When she's running with
full power, the monitor is either fluctuating back and forth near center or
almost to the right side (running rich.)

I've installed the capacitor in the AFM, checked/replaced all grounds,
replaced O2 sensor and Temp II, checked and replaced all vacuum hoses,
checked charcoal canister. New fuel injectors, distributor cap, plugs, and
plug wires less than 5k miles ago.

Thanks for any help here.