just an update on the recent radical drop in fuel mileage i experienced after doing a rebuild on my Carter BBD (87 YJ 4.2L) from about 17-18mpg to something like 5-7mpg! there were no obvious signs of excessive fuel consumption (black smoke clouds) or leaks in the system, and she seemed to run and start ok. turns out to have been rather simple and rather complicated at the same time. when i took the carb apart i noticed that the stepper motor didnt move very freely - the shaft appeared to be sticking in the bushing or something. i pulled the shaft back out so that the pins were in the forward position and put it back together. the next day i did the nutter which recommends placing the pins in the full forward position. now when i got this beast the CTO had been broken off as well as the O2 sensor being disconnected, so i had a pretty good hunch that the stepper motor had been inactive for a long time (hence the corrosion and the sticking). thus i hoped that taking the computer out of the loop would bring the fuel mileage back up (or something like that). i also bypassed the charcoal canister (bad purge valve), retightened the carb mount nuts and the manifolds, and rechecked that there were no vacuum leaks. well none of it worked - and needless to say with gas going for $3+ at the pump it is alarming to practically be able to WATCH your gas gauge drop as you drive down the highway! then a few days ago i remembered that having the stepper motor pins in the full forward position richens the mixture. so i figured - what the hell i'll put em in the full lean position and see what happens. and VOILA! gas mileage is back to ~17-18 mpg and she runs like a top! so CTO and O2 no good -> stepper motor doesnt move -> i 'rebuild' carb and inadvertently put the pins in full forward position -> stepper motor cant move because corrosion/old/POS -> disconnect computer ->
stepper cant move b/c no signal (obviously) -> restore pins to full lean position - problem solved! whew. anyway i just wanted to post about this because while i was researching on this list it seemed to me that i ran across alot of folks posting about their problems, then getting some responses and possible solutions and then nothing else. it would be nice to hear what exactly the problem turned out to be and how exactly it was solved (or not) - at least more often. so here ya go. cheers all and thanks for all the help. bennett