I have a 84 300 I 6. Acouple weeks acouple it just started poping though the carb and didnt have any power. After alittle research and leak down test i though it was a burnt valve, I had a complete valve job done. put all back together yesterday and still poping and want idle or run. What else could it be? I thought maybe jump time but everything I read says the 300's have timing gears? It this true? Please help. Daily driver.

 

Hi Bennett,
Yes, the 300 is a direct gear to gear for the timing, so there would be some serious damage before it "jumped".

I had this issue with my '81 and it turned out to be a series of vacuum leaks. I imagine you still have the color coded plastic vacuum lines. Those get really brittle over time and can crack. Sometimes, they aren't visible because they simply get a series of hairline fractures which, when there's a lot of them, can equate to quite a leak.
If it were me, I'd replace ALL your vacuum lines with new, fresh rubber.

Also, your setup is computer controlled, have you checked the computer for any diagnostics?

 

ok ill look into changing vacum lines. i do still have diagram also. I have not checked computer either, how can I do that?

 

I'm not sure on the older computer setup, as it's something I haven't done before (mine's pre-computer era). Someone else here may know.

But, I'd start with the vac lines. Just do one at a time and take your time. It should make a big difference.

 

One more item to check, worn down/flattened camshaft lobe(s). With the valve cover off, crank the engine over and watch the rocker arms. Disconnect the coil wire, if you don't want the engine to start while performing this check. Won't hurt anything if does, just makes it harder to see how much each rocker is moving.

 

Why would you pull the head before you checked the cap, plug wires, vacuum advance, carb accelerator pump. Any of those could cause popping through the carb. Even if it was a burned valve, it would have to be an intake valve and that is pretty unlikely, plus you could have seen the burned valve when you had the head off.
Now you want to attack the computer, which is a very unlikely suspect.
Always do the simple stuff first. Take care of the routine maintenance (like plugs, cap & rotor, plug wires) and quite often a problem cures itself.