84 tercel sr5

[Petros]

sounds like the spark plugs, wires and cylinders are all working evenly and properly. the power loss is somewhere else. You have check for vacuum leaks I presume, in not do so before you do anything else, it will never run properly with a vacuum leak. Also verify the vac hoses are all routed properly, if they got mixed around it will also act like a vac leak.

have you replaced the fuel filter yet? partially plugged filter will allow it start and run normal, and than cut out at higher speeds or higher engine loads (like going up a hill) because the fuel supply is restricted. The fuel filter is cheap and an easy replacement (buy the same year corolla filter, it costs less and is bigger and fits just fine, you have to switch in and out hoses).

Also, a leaky fuel line up stream of the fuel pump could cause it to suck air, and it will not necessarily leak. by sucking air into the fuel supply line you also restrict fuel intake, this is harder to find, but easy to check each of the rubber fuel lines in the engine compartment around the fuel filter and the fuel pump. there is another one that can go bad over the fuel tank that is hard to reach (you need to drop the fuel tank), but that one going bad is less common since it is out of the weather and not near the engine heat.

Also, verify that the auto choke is opening all the way, and that your throttle cable is adjusted so the throttle opens all the way (have someone step on the throttle while you inspect the linkage and see if you can advance the throttle further by hand, engine off). to see if the choke opens all the way, remove the top of the air filter, engine cold, start and watch the primary throttle on top of the carb, it should have choke closed at strat up, and slowing open within a few min. After it reaches operating temp it should be all the way open. One that does not open all the way will also restrict high end power output.

Good luck.