i have a1986 720, not d21 with a Z24 and a 5speed, standard cab. it wont keep an idle at all. my truck is a total mystery when it comes to miles or what has been done to it, i bought it 2 years ago at a whole sell lot, the odometer said it had a little over 20k on it now it has 45k on it, it wont go over 75 mph now also and ive had it way over 75 mph befor, the gas mileage is slipping and so is power and ive tried alot,ran down vacuum leaks, fuel filter, plugs and wires, distributor cap and rotor button. it also ticks????? it has ticked ever since i got it. everyone ive talked to says they just tick like that. is this true??? so many questions, please give me feedback, let me know if u need anything more specific about the problems.

It may be leaking air in the base of your carb. You may also have a fuel leak under pressure. Look for any gas smells or leaks immediately after trying to run her hard.

The "tick" is not normal, they didn't come from the factory that way. Adjust your valves.

the tick is common in these as they get miles on them... you need to adjust it like pleb said

now the one thing i have noticed is that no matter how well they are running... all of the z24's tick when they're warming up... but once warm it SHOULD NOT TICK!