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Yes, should have put in more detail on the tune-up. All new plugs, wires, cap, rotor. He does have oversize tires on it that are softer than normal, I've mentioned that to him, but would it take 5 or more mpg off? He should be getting mid teens or close on the hiway with the manual OD, 75 is barely over 2000. Long time ago I had a carb'd 305 in a 3/4 ton van and, with an advance curve tuneup, got it up to 15 on the highway with an auto trans without OD and carrying a good load.
And, no, he hardly ever gets the engine
over 2500 even when upshifting. Drives it like a baby. So does his wife (my daughter).
I'm going to recheck his timing, maybe throw a timing tape on the damper and see what he's got. Probly can't change the curve other than to advance initial, if it will stay out of detonation. I was thinking maybe the computer was keeping it in closed (?) loop, like if it
was full throttle. I even asked if his engine was running at the right temp - warm enuf for the computer to go into regular mode. It's got quite a few miles, maybe the 02 sensor could stand replacing. I guess we could check out the temp sensors, too. Anybody know what volts or resistance they should show? If the computer temp sensor is telling the computer the engine isn't warm enuf to go out of cold start "choke" mode, that might do it, too.