My 87 22R w/carb exhibits an extremely lean condition. Here's the long story. I installed a rebuilt carb years ago due to the original carb being all carbonized and gummed up and not allowing the secondary to open. Symptoms were very poor gas mileage and black smoke out of the exhaust After the rebuilt carb installation the truck never ran right. Symptoms were: NO power during normal acceleration; pushing the accelerator further made the truck go SLOWER. When pumping the pedal with little pumps of the pedal (squirting gas into the primary), I could feel surges of acceleration with each little pump. As expected, no amount of idle screw adjustment had any effect. Basically the truck was almost undrivable and the carb vendor showed NO concern. Out of desperation I rigged a short piece of thick wire to hang down into the secondary and keep the plate from opening more than 13/32in. With that setup it would drive acceptably but mileage suffered and reading the plugs showed the mixture to be rich. So I removed the vacuum cap on the upper-most capped port of the three capped ports on the passenger side of the carb. The mileage improved a little (18mpg) and the plugs looked better. I have been running it like this for a couple of years. But recently it's been stalling while idling and backfiring during accelerating. The secondary was beginning to get sticky. So just yesterday I installed a new rebuilt carb and I was hoping that the new unmodified carb might be the answer. No luck; the lean condition problem remains.
I will accept any and all diagnostic suggestions.