i have an 85 trans am with a 79 truck 350 in it, i adjusted the valves by setting them at 0 lash while its running, then shut it off and turn them 1/2 a turn to set them. now it runs great, starts much better, no hesitation or anything but my gas milage is HORRIBLE! should it have affected it that badly?i also have an edelbrock 600 cfm carb. should i re adjust the carb or should i start looking for a fuel leak? if you think its a fuel leak where should i look at? thanks alot

 

I doubt the valve adjustment had anything to do with gas mileage. I'd be more inclined to suspect something else got bumped or altered during the process, or failed or changed at about the same time.

Check to make sure the timing isn't grossly retarded, and the vacuum advance is hooked up and working.

 

what could i have bumped or altered? i didnt touch any fuel lines and they are still hooked up and in good shape. timing shouldnt have jumped from just pulling off the valve covers. i just had the carb set and the timing set by a gm mechanic i know so the vaccume advance and timing should still be right on the money. i have no idea what could have happend to make it soo bad. and i have no idea how i can fix it

 

Half a turn is kind of a lot after zero lash isnt it? I always do mine 1/4 turn after zero lash while the engine is running. Much better that way.

 

the 1st time i did it, i did 1/4 turn at zero lash, but it didnt do anything but make my gas milage worse, still had a hesitation and stuff so then i did 1/2 turn, didnt really hurt the milage but it took out the hesitation and fixed all the performance problems i had with it. it runs awsome but now my milage sucks. 1/4 turn wouldnt affect it that much would it?

 

The factory says one full turn; so no, ½ turn is not alot, that's about what I use for a street-driven motor.

My opinion hasn't changed; the valve adjustment is not the problem. Something else was disturbed, or broke at about the same time. Forget the valve adjustment if you did it right which it sounds like you did. Look at your carb, vacuum lines, fuel lines, gas tank, timing, wiring, etc.