I have a 79 with a 302 with the original 2 barrell carb. The carb started acting up so I took it apart and cleaned it. Now the valves rattle when it shifts into high gear and at steady highway speed. it doesnt do it any other time. Do I need to adjust the carb some or what. I hate to mess with it to much because it runs great but I want to get the valves right. The motor never done this before I took the carb off so I know its something I have done. I'm not a real good carb guy but I will try anything if you guys can help me out. Thanks Scott

 

What valves are talking about?

 

Valves in the heads or it might be the lifters. It didnt do it until I took the carb off and cleaned it.

 

What you're hearing is 'ping' (pre-ignition) which is not good to hear. Could be because of the rebuild you are running the carb leaner, which will cause the ping, or the timing is off. Check timing first, then look at maybe backing the idle screw out a bit. All vacuum hoses correctly hooked up?

 

pinging aka detonation aka valve rattle (thats a really misleading term) while under light throttle can be caused by too much vacuum advance. Check base timing first as suggested above. If thats ok try unhooking the vac advance, plug the hose and drive it. Adjusting the idle mixture richer to compensate for a lean higher rpm condition wont work... it would have to be way rich at idle.

 

Thanks for the help. I'll check the timing tomorrow. I really think its the carb because it didnt do any of this untill I cleaned it. I will check it out and get back with you guys. Thanks again. Scott

 

the carb needs readjusted since the rebuild.

 

Did the truck originally have an EGR valve and is it hooked up? I've seen cases of severe pinging on carbed vehicles that were traced back to a non-operative EGR valve. If the carb is jetted and calibrated for use with an EGR valve, it will run too lean without one.

 

Mine was doing that util I switched to a higher octane fuel; I also would add octane boost if I filled up with regular.

 

I put 93 octane in it and played with the timing. Its helped some but not stoped it. I'm going to set the timing back somemore and see where that gets me. Scott