Just rebuilt 1987 22r toyota truck. Has new head and timing chain. it happy to accelerte up to 90 miles per hour. However, if you take your foot of the gas say at 70 mph to decrease to 69 it bucks really hard. Whenever you remove the gas or start to slow down it bucks. any idea's ? truck has carborator, electronic ignition. it happy to start and idle normal

I would look at the fuel level in the carb and make sure it is at the correct level. This is set by adjusting the float tab in the carb fuel bowl. I would also look at the accelerator pump and make sure the membranes don't have a hole in it or spring in backwards, or is leaking. It sounds like too much fuel is being squirted into the carb with the slightest movement of the accelerator. My Truck was a 1987 California emission vehicle. (Way too complicated carburetor vacuum controlled mixture emission system) I found when ever I did a "carburetor kit", every so many years, it would work great. Since you did a rebuild, and had everything apart, I would just make sure all the vacuum lines and one way valves are correct per the diagram under the hood. There are also some lines that are run through temp sensors on the engine so when it warms up, the vacuum is cut off. My trunk had a "cold engine pump". The vacuum control was shut off when the engine was warm. It would squirt extra gas into the carb to keep the engine from stalling when cold. If the engine is hot, it was too much fuel.

With the engine running and hot, set the parking brake and run the engine to 2500 or 3000 RPM with the air cleaner lid off. Move the throttle back and forth and see if you can see fuel being squirted in or not. Please be careful and wear eye protection just in case of flame back.

I think doing a careful carb kit and cleaning, plus verifying your vacuum line connections will take care of this problem. What ever you do, don